A Four Facet Drill Sharpener with Optional Point Splitter
Click to enlarge
Four facet drill points work well, with some advantages over the more common conical point. Less tendency to walk, reduced thrust, and longer life are claimed by Joseph Mazoff in his "Drill Point Geometry"[1] document. Adding Secondary Point Angles (SPAs) improves the drill's self centering tendency, improves hole finish, reduces drill wear, and reduces the exit burr when through drilling. With all these claimed benefits I began looking for a way to try four facet sharpening and SPAs in my shop.
Four facet drill sharpeners are not common in home shops, probably because they're more expensive than conical point sharpeners. I built D.A.G. Brown's hand powered four facet sharpener[2] for small drills and found the drills worked well. So I expanded to faceting larger drills and adding secondary point angles using Ian Bradley's hand powered Honedrill[3]. A drawback to these hand powered methods is that centering the drill point is a judgment call rather than being accurately set by the jig. Plus, drills over 1/4" take some time and effort to sharpen using hand power. I experimented with powering the Honedrill but found setup wasn't fast or easy so I use this only for drills larger than 1/2".
Eventually I designed and built the powered four facet plus SPA sharpener described here to handle drills from 1/2" to 1/16". This design depends directly on familiarity with structure of a twist drill body and how this is used to advantage in four facet sharpening, leading to the following overview.
Sharpener Design Concept and Initial Design Choices
Four facet sharpening takes advantage of the fact that the cutting lips are parallel to a line through the center of the drill face and extend in front of this center line; the blue in Figure 0 shows this area. The blue area is ground at the primary relief angle while the red area is ground to a larger secondary relief angle so the heel clears the work. All four facets meet in the center of the drill face so the center is pointed rather than the flat chisel common with conical sharpening. This pointed center minimizes wandering at the start of drilling and allows starting nicely in a center punch mark.
The notion behind this sharpener is that if a drill bit is sequentially pivoted (to the primary and secondary relief angles) about a theoretical center line on the face of the drill (parallel to the cutting lips) and traversed past a flat grinding wheel, then indexed and repeated for the other side the result will be four facets. Adding Secondary Point Angles requires simply changing the angle of the drill body and infeed to grind the outer corner of the drill lips.
To position a lip parallel to this theoretical pivot line, starting with the drill body parallel to the motor arbor or rotor, the drill body is angled in the horizontal plane by 31 degrees for 118 degree drill points or by 22.5 degrees for 135 degree drill points. Maintaining the drill's axis horizontal, its center is positioned at the pivot line and the drill is rotated about its axis so a lip is parallel to the pivot line, i.e. horizontal.
The SketchUp model in Figure 0A illustrates the concept, where the drill is rotated in the horizontal plane so the center of the drill face lies along the pivot line. The pivot line is shown explicitly. Visualizing the positioning of the drill and the required motions may be difficult at this point but should become clearer as you read how each of these details is handled.
A horizontal pivot line was chosen for simplicity. To implement this design the plane of the grinding wheel must be vertical and positioned precisely at the pivot line. The drill must be held with its center on this pivot line. One flute's cutting lip should be parallel to the pivot line and the drill must be accurately and concentrically rotated axially about its center by 180 degrees to sharpen the other side. Pivoting vertically to the chosen relief angles allows grinding the facets.
Since the drill face must pivot about a line and also traverse past the wheel along that line a trunnion is used to avoid conflict between the wheel and the drill support. Using a trunnion table, the parts are small and light plus traverse is linear. A flaring cup grinding wheel provides clearance for one side of the trunnion; the left trunnion support extends inside the wheel as seen in the pictures. The wheel should be CBN or diamond because they retain their shape for long periods. Refreshing the face of an alox wheel removes a couple thou and this would require realigning the wheel face to the pivot line -- which takes some fussing, as described later.
Initially, shop made collets were tried because the holder could be shaped so the drill would have minimal extension from the collet without conflict between collet holder and wheel. Unfortunately collet runout was unacceptable so an ER-20 chuck and collet set was used for its excellent concentricity. This chuck size limits the smallest drill which can be sharpened to 1/16". Smaller drills are too flexible to be sharpened when protruding enough to avoid conflict between chuck and wheel. The chuck holder is easily removable/replacable to allow evaluation of progress at intermediate stages of the sharpening process.
The nut on my ER-20 chuck is 0.775" long and has a 1.338" OD. The size of this nut dictates placement of some holes and parts so using a chuck with a different size nut might require shuffling things around slightly.
This 4 facet sharpener divides naturally into major sections as follows:
- Trunnion table
- Traverse table
- Holder for collet chuck
- Motor and wheel
- Mounting plate for traverse table and motor
- Base to hold unit
The first three sections provide drill orientation and motion control while the remaining three sections concern mounting the completed motion control relative to the motor. The mechanism for orientation and motion control can be completed and then adapted for use with a variety of grinders. The text and drawings will provide sufficient detail to build the orientation and motion control; the motor and wheel setup shown in the pictures are described but not detailed.
The sharpener was tested initially by mounting it on the table of my shop made Brooks cutter grinder. This worked well but isn't practical over the long term because the Brooks infeed functioned to align the wheel to the pivot line - this is an important part of alignment so it is preferably done infrequently and then locked in place. The mount was built to accept the motor I had on hand and a simple traverse was added. I expect builders who choose to make a similar sharpener can adapt what they have on hand to the task.
Considerable freedom is possible in implementing this concept as long as both the grinding wheel and the center of the drill face are kept precisely on the trunnion pivot line. Some thought was needed to ensure there was room to allow positioning the drill to the desired drill point angles so I used SketchUp to model the setup and avoid conflicts. My ad hoc construction approach was to use simple jigs/tools where possible and simple measurements to allow adjusting the pieces to achieve the desired alignment. This accommodates minor deviations in hole positions, etc. but a few items, e.g. trunnion bearings, benefit from careful fitting as will be noted in the text.
Construction of the motion control is described below, along with the optional point splitter. This sharpener was built from scrap because it was unclear whether it would be successful. A more attractive unit could easily be built from purchased materials, of course, but this one works well so it's a keeper. In some cases sizes were compromised slightly based on size of items in my scrap bin so the more appropriate size will be suggested in the text and drawings.
Trunnion Table
The trunnion table tilts to the desired primary and secondary relief angles. The chuck holder mounts on this table at an angle so one cutting lip of the drill is parallel to the trunnion pivot line, i.e. the center of the trunnion. Infeed is used to advance the center line of the drill face to the pivot line. The trunnion table simply supports the chuck holder at the correct height and point angle, allowing selection of the relief angle by pivoting. The default drill point angle is 118 degrees but other point angles (e.g. 135 degrees) can be accommodated.
My trunnion table is 3.625 wide by 3.5 deep and 0.072 thick (based on a scrap of ground plate) but this doesn't leave much room for the hole needed for 135 degree drill points. Better would be 3.625 square by 1/8" thick, HRS should work fine.
The first item to make is the trunnion alignment tool, which means choosing the diameter of the trunnion. I used 7mm (0.274") rod from a line printer but 1/4" drill rod would work fine. A straight piece about 6" long needs a 1/2" wide slot milled to exactly half the diameter; this should be about 2.25" from one end. Mill a little less than half diameter and then use a pattern file to get it to precisely half diameter. At the short end add a similar section about 1/4" wide. It's easy to measure slot depth and it's worth fussing a bit to get these right since the drill center height alignment depends on it. Verify the tool remains straight after making the flats and correct as needed.
Next make the two trunnion holders that bolt to the trunnion table as shown in Figure 1. These need to be identical so cut them to approximate length then hold them together in a vise and drill the #31 alignment hole through both. Ream to 0.125, press fit an alignment pin (I used drill rod) in one with about 1/8" protruding; ream the hole in the other piece so it is easy to fit them together and get them apart. Plan ahead so the alignment pin will be toward the center of the table when the holders are on the table (else it will conflict with the trunnion support on the traverse table), see Figure 2.
With the holders pinned together and back in the vise, drill the hole for the trunnion slightly under size. If you have a reamer for the trunnion, ream to size -- a good fit here is important. Alternatively, use a lap made from aluminum to size the holes. (Some line printers have bearings that can be liberated from their carriage and used by making larger holes and pressing them in, which is what I did here.) Cut a piece of trunnion material slightly shorter than the combined thickness of the two trunnion supports and use this through the bearing holes - in combination with the small alignment pin this ensures alignment of the trunnion holders while finishing the outside.
Machine the outer edges as needed while keeping the parts pinned together. I tidied up the finish on all but the bottom on the bench sander. The bottom is machined at 20 degrees to provide the needed wheel clearance, see Figure 1. This angle causes the center of the trunnion to lie above the bottom edge of the trunnion holder.
Size the trunnion table, Figure 2, to 3.625" square and drill only the two pilot holes in the right front corner (0.3" and 0.7" from the front edge), used to hold the trunnion support. Position the trunnion holder at the right front corner and drill through the pilot holes. Drill and tap these holes in the trunnion holder for 8-32x1/2" socket head screws. Open the pilot holes in the trunnion table to clear the 8-32 screws.
Loosely bolt the right trunnion holder to the trunnion table. Use the trunnion alignment tool through the hole in the right trunnion holder and place the other trunnion holder onto the tool at the left side of the trunnion table but facing in the opposite direction. This will leave about 1" at left front of the table open to be removed later. Adjust the right trunnion holder as needed to position the alignment tool parallel to the front of the trunnion table. Open the clearance holes in the table slightly as necessary. Tighten the screws holding the right trunnion holder and verify the alignment tool is parallel to the front edge of the table.
With the alignment tool holding the left trunnion holder in place at the left edge of the table, mark its position. Install the left trunnion holder using a similar approach as used with the right holder. It may take a little fiddling with the position of the holders but the alignment rod needs to slide and rotate with modest friction when both holders are securely fastened.
Place a machinist square on the trunnion table with the blade pointed up. Put the blade against the flat in the slot of the alignment tool and mark the position of the center of the alignment tool onto the table. This line should be close to the edge of the left trunnion holder at its base. Remove the material from this line forward as shown in Figure 2. Dimensions for this aren't shown on the drawing because they may vary slightly between units but it will be about 1". Drill a #31 hole 1.05" from this line and 1.9" from the left edge per the drawing, ream to 0.125".
While sharpening drills the collet holder is removed to check progress and then replaced on the trunnion table. Alignment pins in the collet holder mate with holes in the trunnion table to ensure accurate replacement. I used my mill+DRO as a jig bore to accurately position the holes but a simple drill jig should work fine. A 1/4" wide piece of steel 2" long with 1/8" holes spaced 1.5" apart on the center line will do; a 1/8" pin in one hole simplifies use. This jig can be used to put the 3 additional holes in the trunnion table per the drawing. Use the back edge of the table as the reference for the protractor. With the jig's pin in the forward hole, align the jig at 30, 59, and 67.5 degrees respectively and drill the 3 holes shown in Figure 2. The jig is used again to space the holes for the alignment pins which mate with these holes.
Holder for Collet Chuck
The holder for the collet chuck provides 180 degree indexing and infeed control as well as locking the chuck in place while grinding. Locating pins allow removal and accurate replacement on the trunnion table so sharpening progress can be evaluated easily.
I used an ER-20 collet chuck from CTC Tools (no affiliation, just a customer), their part# = F95 with a 1" by 4" shank. The largest ER-20 collet is 13mm but the ID of this chuck's shank was 11mm so I drilled it to 1/2" and then bored it to 0.535 - the chuck is hardened and ground so my 1/2" drill took a beating; it became one of the early test drills for this sharpener.
The holder for my chuck is 1.3" high by 1.2" wide and 2.5" long, see Figure 3 (rectangular or square material 1.25" or larger on a side should work with minor adjustments). The sides of the holder must be accurately parallel to accommodate verification of 180 degree indexing using the test described later. Center in the 4 jaw chuck, step drill to 7/8" and then bore out to pass the chuck shank. To get a good fit here I lapped the last couple thou since I don't have a 1" reamer. Face the end to ensure it is perpendicular to the bore. Use this as the rear face and add the 0.125" hole for the index pin 0.650" from the center of the bore. Add the 10-32 (or M4x.7) threaded hole for the bolt to secure the chuck and make a brass 10-32 locking bolt 5/8" long overall, knurled for about 3/16".
The chuck holder will bolt to a pad that brings the drill point up to the pivot line, see Figure 4. This pad should be 1.2" wide and 2.95" long (my pad is a little shorter so the chuck holder extends beyond it slightly). This pad should be 3/8" thick initially and will be adjusted as described below to place the chuck center at the pivot line height. Drill and countersink clearance holes in the pad for the 4-40 screws which will secure it to the chuck holder, Figure 4A. Align the back of the holder with the back of the pad; drill and tap matching holes 4-40 in the chuck holder (the holes can go into the bore to make tapping easier) and bolt them together. Remove burrs and chamfer edges and holes so chuck holder and pad fit nicely and so the pad mates well with the trunnion table. Place the chuck in the holder. Use the brass locking bolt to secure the chuck and add tape to the back end of the chuck so it doesn't slide out of the holder accidentally. This tape has saved my chuck a couple times...
The OD of the collet nut conflicts with the pad so the front of the pad needs to be relieved slightly. I set a fly cutter so the radius was slightly larger than the nut's radius and marked the area to be relieved on the pad. The pad was mounted in the mill vise with the area to be relieved vertical and centered on the fly cutter. The fly cutter was brought down slowly to remove the material with the curve matching the nut, as shown in Figure 4.
Another simple tool is needed to judge the chuck height vs the pivot line. This tool is a short piece of round with a half-diameter flat on the end for about 1/4". Diameter isn't critical, a bit of the trunnion material would work fine. The half diameter section should be done as described earlier. Select the appropriate collet and tighten the chuck onto this tool with the flat projecting from the collet.
Slide the alignment tool into the trunnion holders and orient the flat up and near the center of the trunnion table. Place the chuck and holder/pad on the trunnion table, avoiding any contamination between the surfaces. Orient the flat held in the chuck so it is facing down, position it over the flat on the alignment tool and measure the difference in height; a gap gauge works well for this. Fly cut the top of the pad to bring these two flats to the same height. (I deliberately reduced the pad thickness to about 0.010" less than needed, then shimmed to get it exact.) It is important to get this right -- it sets the drill's center height at the trunnion pivot line, one of the key points mentioned earlier.
The index/infeed ring, Figure 5, was made from 1.5" aluminum round but other materials would work fine. Although the figure shows the ring as 0.6" long, 0.75" or so would facilitate the "scootch" maneuver (described later). I chucked the round and knurled it for the length of the ring, then turned it to remove the knurl from the first 0.3" (or 0.45 for the longer version). Drill two 0.125" holes 0.650" from the center 0.35" or 0.5" deep and precisely 180 degrees apart. This is important since it is used to index between the drill lips (a procedure to minimize indexing error is provided below). Remove the material for 180 degrees between these holes so the index pin on the back of the chuck holder can pass. This will leave about half of each original 0.125" hole in the ring. Drill and tap 6-32 a hole 0.630" from the center, mid-way between the first two holes and on the side away from the removed material per Figure 5. Bore the center of the ring to a good fit on the chuck shank, then part off. A 1.25" long 6-32 (or M3x.5) socket head bolt is used for the infeed; round the end slightly for good contact with the chuck holder, add a washer and small spring to take up slack in the threads and install in the index/infeed ring. See Addendum for a better infeed screw design.
Add (perhaps temporarily, see index test below) the 0.125" index pin to the chuck holder, extending from the holder 0.3" or 0.45"; chamfer both ends of the pin. Install the index ring on the chuck shank and put the chuck in the holder. Rotate the index/infeed ring clockwise so it is against the index pin. Mark the ring on the left side at center height; drill and tap 10-32 (or M4x.7) on this mark just clear of the knurl. Make and install a brass locking screw, 0.75" long overall, threaded for 3/8", remainder knurled.
The sides of the collet holder are assumed to be parallel, as specified earlier. A pin is gripped in the collet and then the chuck holder assembly is held vertically in a vise by gripping this pin as shown. I used a surface gauge with its locating pins running on the front edge of the vise's movable jaw as a reference. The DTI finger touches the side of the chuck holder, allowing the side to be rotated until parallel to the front of the vise. Once parallel the chuck lock is used to hold it in place, then the index ring is rotated against the stop, lifted up away from the chuck a few thou and locked to the chuck. The chuck lock is released and the chuck holder rotated so the index pin is against the other side of the ring. The chuck is locked and the DTI is used to verify that this side of the chuck holder is now parallel to the vise front edge. If the rotation is not 180 degrees per this check, re-work the index ring or replace the index pin with one of the diameter needed, sizing one end to fit the 1/8" index pin hole. This test is sensitive - a change of 1 thou over 1.2" is about 0.05 degree. (There are other, similar ways to check rotation, e.g. using a DTI held in the mill spindle.) This adjustment ensures the lips will be ground exactly 180 degrees apart.
Assemble the chuck, holder, and index ring. Place a pin with a flat end in the collet and set up a mag base and holder as shown in Photo 1 with the DTI finger on the center of the pin. Advance the infeed screw so it is holding the infeed ring clear of the chuck holder and lock the index ring to the chuck (ensure the chuck nut is slightly clear of the holder). Rotate the index ring against the pin and zero the indicator, holding light pressure to ensure the infeed screw is against the chuck holder. Rotate the chuck 180 degrees so the index ring contacts the pin going the other way, hold light pressure and verify that the indicator reads zero. These readings 180 degrees apart should match because this surface was faced earlier. If the readings differ by more than a couple tenths repeat to verify, then use fine carbide paper on a flat surface to tweak the back of the collet holder and improve the situation. This ensures the drill lips will be ground to exactly equal length.
Add 0.125" locating pins in the bottom of the pad, see Figure 4A (the 0.201" should be 0.200 but it is complicated to fix in the model). These pins should be pressed in and extend about 1/8", rounded on the end to help in locating the matching holes in the trunnion table. Try inserting the pins into the holes in the trunnion table and make minor adjustments to the table with a round needle file as needed to achieve a snug fit while ensuring ease of insertion and removal. A somewhat tight fit initially is OK, they'll wear in quickly.
Traverse Table
The traverse table connects to the trunnion table via trunnion supports bolted to the traverse table. With the trunnion table set to the relief angle and the chuck holder mounted to it, the traverse table is moved laterally to grind a facet on the drill. A traverse lever provides motion control using a reduction of about 4:1.
Make the trunnion table supports for the traverse table from 1/2" steel per Figure 6. Use 6-32 socket head screws to hold the overhanging section onto the left support (or make it in one piece by milling); countersink the heads but not so far that they conflict with the hole for the trunnion. As usual, drill the trunnion holes under size and then enlarge with a reamer or by lapping to obtain a shake free fit. Use a short length of trunnion material through the two supports and adjust the bottom surfaces so both make complete contact with a flat surface. This to avoid binding of the trunnion alignment tool from height difference after installation.
My traverse table is a 4.25" by 5.5" rectangle of 1/8" steel, where the long edges must be accurately parallel (a slightly larger 4.5" by 6" table would make positioning vs the wheel easier). The simple traverse bearing used is a slot in HDPE or UHMW plastic through which the front and back edge of the table slide. A smooth surface or grind marks parallel to the long edge on the top and bottom table surfaces will ensure free movement through these bearings -- a pass with the bench sander may be helpful.
The approach here is similar to that used in constructing the trunnion table. Drill only the two pilot holes in the right front corner (0.3" and 0.7" from the front edge) used to hold the right (non-overhung) trunnion support. Position the trunnion support at the right front corner and drill through the pilot holes; since this support is symmetrical, add a witness mark so it can be removed and replaced without experimenting. Drill and tap these holes in the trunnion support for 8-32x1/2" socket head screws. Open the pilot holes in the traverse table to clear the 8-32 screws.
Loosely bolt the right front trunnion support to the traverse table. Use our old friend, the trunnion alignment tool, through the hole in the right trunnion support and place the other trunnion support onto the tool at the left side of the traverse table with the over hang facing forward so it can (eventually) go inside the wheel. Adjust the right trunnion support as needed to position the alignment tool parallel to the front of the traverse table. Open the clearance holes in the table slightly if necessary. Tighten the screws holding the right trunnion support and verify the alignment tool is parallel to the front edge of the table.
Place the trunnion table onto the alignment tool between the supports. Position the left trunnion support so there is 0.05" or so space between the table supports and the trunnion table holders. Mark the left trunnion support's position, remove the trunnion table, and install the left trunnion support using a similar approach as used with the right support. It may take a little adjustment to the supports but the alignment rod needs to slide and rotate with modest friction when both supports are securely fastened to the traverse table.
Make the trunnion pins about 0.15" longer than needed to allow for felt washers on either side; a little longer is OK because it is easy to face them to fit later. Drill and tap both ends 6-32, make 1/2" washers to capture the felt washers. Make felt washers to minimize entry of grit into the trunnions (although it's unclear whether they're really needed). I haven't oiled anything on this sharpener, it hasn't been necessary -- on grinders oil can capture grit and become lapping paste. The felt washers were included in case oil was needed on the trunnions plus they keep the trunnion table centered between the supports. Slight movement of the trunnion table laterally on the trunnions won't affect sharpening.
Use the trunnion pins to temporarily install the trunnion table to the traverse table. Make a support leg for the back of the trunnion table to prevent the front of the table from contacting the wheel inadvertently. I used some scrap steel 3/8" by 1" wide by about 1.2" high; the height of this leg should be chosen to set the desired minimum relief angle. Use the trunnion alignment tool plus a square placed on the traverse table to judge wheel clearance - the front of the trunnion table can be relieved slightly if needed. I set the minimum table angle to 5 degrees which provides adequate wheel clearance but if you expect to use relief angles less than 5 degrees then relieve the front of the table so it doesn't contact the wheel. An alternate method of setting the minimum table angle is to use a bevel protractor as shown in Photo 2. Mount the leg at the rear of the table so its rear edge is even with the table (to allow the eccentric to pass when setting small angles) and left of center slightly so it doesn't interfere with the chuck holder. The bottom of the leg should angle forward toward the wheel about 10 degrees. Use a 4-40 flat head screw to secure it.
Make a 1.5" diameter disk 0.2" thick from steel. Chamfer the OD with a file or graver to round it slightly, then part it off. Drill an 8-32 clearance hole about 0.45+" from center. Mark the position for this onto the leg so the low point of the eccentric allows the leg to just touch, drill and tap the leg for an 8-32 socket head screw; use washers on both sides of the eccentric.
To calibrate the eccentric, use a setup similar to the protractor arrangement shown in Photo 2. Rotate the eccentric to set the table to 5/10/15/20 degrees and mark the eccentric with ink at the low point for each. Use a chisel or center punch to make the inked fiducial marks permanent, then add numbers with a number punch set. A degree or so error in calibration is acceptable since the actual relief angle isn't critical - what's critical is that the primary relief angle be the same on both cutting lips.
In use, primary relief is set based on drill size while a single secondary relief will work for all drills to be sharpened with this unit. Secondary relief is set by a small triangular flipper bolted to the side of the support leg, as seen in Photo 3. Size isn't critical, 0.9" wide at the base and 1.6" to 1.9" high, made from 1/8" aluminum. The bottom rear interior angle is 80 degrees to provide an over-center action in use. Drill a clearance hole near the top of the triangle for an 8-32 screw. 
Set the table angle to about 20 degrees (20 to 28 will work OK) using a pad under the eccentric, then mark the side of the support leg through the hole at the top of the triangle, drill and tap 8-32. Install the flipper leaving the bolt just loose enough so the triangle will operate by gravity.
An optional rotation stop at 28 degrees can be added to the left trunnion support if desired, see Photo 3. This helps protect the wheel from damage in transit should the table flip upward.
Photo 4 shows the location of controls on the orientation and motion control module.
The traverse bearings can be made from HDPE or HMWP since both are slippery and easily available. I used a piece 0.75"x0.52"x 2"; a 1/8" slot was cut 0.175" deep along center of the narrow edge. This plastic rebounds slightly when cut with a slitting saw so the slot is actually about 0.121" high and grips the 1/8" thickness of the traverse table edge nicely. This bearing was cut into four equal parts and 4-40 clearance holes were drilled for mounting.
Mounting Plate and Base
The mounting plate must be large enough to hold the motor in the proper relation to the traverse table. The motor size, wheel size, and the method described below for positioning the traverse bearings will dictate the minimum size for the mounting plate. After everything was mounted on the plate I inset it into a wood base and added rubber feet plus a wooden rack for the collets. Wood is light, making it easily portable.
Motor Considerations
This is a drill sharpener meant to resharpen dull drills, so only modest power is needed. I repurposed a 0.035HP 1400RPM motor which is barely adequate but a 0.25HP 3600RPM ball bearing or similar motor would be a better choice. My motor uses plain bearings so it "woodpeckered" while grinding until I added a crude thrust bearing consisting of a single ball held in the cupped end of a screw as shown in Photo 15. Also visible is the rubber mount that in some cases causes slightly curved facets.
My preference is to have the wheel rotate CCW as seen by the operator because it leaves less of a wire edge but either direction will work. Reshaping heavily damaged drills is more effectively handled with a more powerful grinder followed by finishing up on this unit.
Motor diameter and mounting method are considerations. A large diameter motor will place the wheel center higher with respect to the mounting plate; this may require pads to raise the traverse table bearings so the pivot line approximately matches the wheel center. The motor mount must provide a convenient way of moving the motor axially to advance the wheel face exactly to the pivot line. My motor included a mount that had a large pin on one side, parallel to the rotor. This pin passes through a hole drilled in a plastic block where sufficient room was left to allow moving the motor axially about 1/4". The other side of the mount has a flange so a clamp is used to lock this to the base plate; loosening one screw allows adjusting the motor position, constrained by the pin. To position the wheel face to the pivot line an indicator is used against the front of the motor, the clamp is loosened, and the motor is bumped gently with a rubber mallet to get the desired movement per the indicator.
I chose the motor/table relation to get double duty from two of the traverse table bearings. The left front bearing is positioned so it supports the table at its rightmost excursion with the left trunnion holder about 1/8" from the inside of the wheel. The right front traverse table bearing also serves as a traverse stop (contacts the right table support) on my unit. Position the right front bearing so the right table holder is about 1/8" from the wheel when traversed full left. The handle of the traverse lever contacts the left rear bearing to prevent over travel in the other direction.
The front two bearings were loosely mounted to the base plate with 4-40 oval head screws, the traverse table's front edge was pushed into the bearings firmly so they swiveled to seat against the table's edge and the screws were tightened to hold the bearings in place. The rear bearings were pushed firmly onto the edge of the traverse table, held there and holes were drilled and tapped for mounting and the bearings bolted in place. A small sealed ball bearing was mounted on an eccentric and placed at the edge of the traverse table, see Photo 5, directly in front of where the wheel contacts the drill. This bears against the table edge to ensure the pivot line can't move away from the wheel. It is made from a round of length equal to the table height, turned down on one end to fit the bearing; an axial hole to clear a 4-40 screw was drilled off center to make it eccentric. This eccentric allows adjusting contact force between the bearing and table edge.
Traverse is handled with a simple lever and link having about 4:1 reduction as seen in Photo 5 . More line printer rod with a rubber roller from that printer for a handle.
Aligning the Wheel Face to the Pivot Line
With the motor+wheel and traverse table bolted to the mounting plate in approximate position, the accurate alignment of the wheel to the pivot line is done by successive approximation. Remove the right trunnion and install the trunnion alignment tool in its place, moving the half diameter section on the end to about the mid point between the trunnion holders - the other flat on the tool should be near but not enter the trunnion support. Rotate the tool so the flat at the end is vertical, then traverse the table so the flat is adjacent to the wheel. Move the motor forward or back as needed to position the wheel face exactly even with this flat. This coarsely aligns the wheel to the pivot line, generally within a couple thou - close enough to use the technique described below.
Another simple tool, a rod with a 0.45" deep flat bottom hole in the end, is helpful to quickly set the distance drills extend from the collet. A 2" or so length of 3/4" diameter mild steel rod is needed for this. End drill it about 0.45" deep. Use a 2 flute end mill held in the lathe tailstock to enlarge the hole to 1/2" and flatten the bottom of the hole. It is easier to face a little off the end than deepen the hole later so err toward deeper. Less drill extension provides better support but the drill must extend enough so the wheel doesn't contact the face of the chuck while grinding the secondary relief. This conflict may be minimized by care during traverse so use your judgment to reduce the extension to an amount you're comfortable with but start with 0.45" and work from there based on experience (note that collet position relative to the nut face varies a bit depending on drill size). Both the collet and the nut move back slightly during tightening but the nut moves farther. If you intend to add the optional point splitter, make a similar 1" deep hole in the other end of this tool.
A steel test pin in the 0.1" diameter range is used to refine alignment. This pin should have an approximately flat end, the shank end of a small drill will work if no pins are available. Install the pin in the appropriate collet, place it in the chuck and hand tighten; over 1/2" should extend from the collet. Use the tool to set the extension to 0.45" by pushing the pin into the collet until the tool contacts the collet face. Secure the pin by tightening the collet chuck with wrenches and push the chuck into the holder until the nut contacts the holder; lock the chuck.
Grinding primary and secondary facets on the end of a flat pin produces a simple pattern that allows judging the position of the wheel vs the pivot line. So next we'll "sharpen" the end of the flat pin where the procedure is similar to sharpening a drill -- except there are no cutting lips to align horizontally.
Place the chuck holder in the 59 degree holes on the trunnion table. Set the primary relief angle to 15 degrees. Ink the end of the pin with a dark Sharpie. Lift the trunnion table to allow the triangular part to support the trunnion table at the secondary relief angle. Traverse so the pin is opposite the wheel. Loosen the chuck lock and the index lock, then carefully slide the chuck forward until the pin just touches the wheel and tighten the chuck locking screw. Ensure the infeed screw is projecting about 0.1" from the index ring, rotate the ring until it contacts the index pin, press the ring forward so the infeed screw is against the chuck holder and lock the index to the chuck. Traverse the pin to the right, away from the wheel.
Use the infeed to advance the pin toward the wheel by a couple thou - loosen the chuck lock to allow the chuck to advance, of course, then lock it again. Turn the motor on and grind the pin at the secondary relief angle. Rotate the chuck 180 degrees and lock, then grind the other side of the pin. 
Advance the infeed a couple thou and grind both sides again; repeat until the end of the pin is ground such that the secondary facets meet and all the ink is ground away. Remove and replace the chuck holder as needed to view progress.
Once the secondary facets meet, re-ink the end of the pin. Flip the triangle forward to set the trunnion table to the primary relief angle. Don't advance the infeed, just grind the primary relief at the last infeed setting used when grinding the secondary relief.
This should produce a pattern similar to that shown in Photo 6. The primary (un-inked) facets here don't meet in the center so the wheel must be moved away from the table a couple thou and the test repeated. If the primary facets meet and overlap then the wheel must be moved a couple thou closer to the table. To accurately judge axial movement of the wheel use an indicator against the motor or wheel while adjusting. Repeat this test/adjustment until the facets meet in the center.
Alignment will be very close at this point. Final alignment is done by sharpening a drill (see below)of about 1/4" diameter, verifying that the primary facets meet in the exact center. Fine tune by moving the motor as described above to correct any minor discrepancy. If you have trouble getting the alignment exact, err on the side of having the facets not meet in the center. This leaves a very short chisel in the center and works well, much better than having the primary facets overlap. (Small mismatches of a thou or two can generally be corrected by making an additional pass on either the primary or secondary facets, as appropriate.)
Drill Sharpening
As with any grinder, wear glasses and/or a face shield. It is hard on the wheel to grind more than a few thou per pass, deep grinds will round the corner of the wheel prematurely so back off the infeed and make multiple passes as needed. The procedure for sharpening drills with this unit differs from that used with conical sharpeners so it is described in some detail below. The secondary relief is usually ground first, then the primary relief optionally followed by SPA's. See Photo 4 to locate the referenced controls.
Loosen the index lock and the chuck lock; slide the chuck forward and lock it. Remove the ER-20 nut from the chuck.
Select the correct collet size for the drill being sharpened by trying it, using the smallest collet which accepts the drill. Install the collet in the ER-20 nut and thread the nut onto the chuck. Use the relief table in Figure 8 (adapted from Moltrecht[4]) to find the primary relief angle for use with this collet and set the relief eccentric to this angle. Primary relief can be reduced for hard materials and increased for soft materials. It is easy and worthwhile to experiment. Smaller primary relief angles are often helpful with typical home shop equipment.
The Mazoff article says drills commonly have excessive relief; a primary relief angle between 5 and 12 degrees works better according to this article - where harder materials drill best with angles toward the smaller end of the range. Worth trying as an alternative to the Moltrecht chart.
Place the drill in the collet with an inch or so protruding and tighten it finger tight, just enough so the drill doesn't move easily. Use the tool constructed earlier to push the drill into the collet until the tool contacts the collet - the drill will then protrude 0.45". Tighten the collet firmly using an open end wrench on the chuck body and a socket or box wrench on the nut. Move the chuck back into the holder until the nut contacts the front of the holder. Rotate the chuck to orient the drill lip horizontal (err in the direction such that the primary facet is wider at the outer edge) and use the chuck lock to hold it in place.
Back the infeed out so it doesn't protrude from the front of the index ring. Flip the secondary relief triangle forward, allowing the trunnion table to be supported by the primary relief eccentric. Place the chuck holder into the 135 or 118 degree point holes on the trunnion table. Traverse to place the lip to be sharpened directly in front of the wheel rim.
"Scootching" moves the drill+chuck forward without rotating it. To do this, lock the chuck, unlock the index ring and slide it back a little while maintaining contact with the index pin, then lock the index ring. Loosen the chuck lock, slide the chuck forward while maintaining contact between the index ring and index pin, and lock the chuck. By locking the chuck or index ring alternately while maintaining contact between the index pin and index ring the chuck can be moved forward or back without rotating. A longer index pin and wider index ring (as suggested earlier) allows each scootch to cover more distance.
"Scootch" the chuck forward until the lip just touches the wheel and lock the chuck in position. Adjust the index ring so it is about 1/10" from the back of the chuck holder, maintaining contact with the index pin, and lock it to the chuck. Turn the infeed clockwise until the end of the screw touches the back of the chuck. Note that counterclockwise rotation increases the feed but the chuck lock must also be released to allow forward movement. A typical feed increment is about 3 thou, about 10 degrees rotation of the 32tpi infeed screw. A "T" handle Allen wrench is useful for adjusting the infeed.
In converting a conical drill to four facet, flattening the conical shape requires the secondary relief pass remove several thou on drills larger than about 1/4". On these larger drills, loosen the chuck lock and turn the infeed clockwise to reduce the infeed. This will then need several passes with increasing infeed to complete the secondary relief facets. Drills previously faceted are sharpened quickly, generally needing only one or two passes.
Traverse the table to the right, away from the wheel. Lift the trunnion table so the secondary relief triangle drops down and supports the table. Turn the motor on, squeeze the chuck holder to the trunnion table with one hand; traverse and return to the right. Loosen the chuck holder, rotate the chuck 180 degrees and lock it again. Repeat the traverse procedure. Traverse to the extreme right and pick up the chuck holder to see if the secondary facets are complete. If not, add infeed of 3 thou or so and repeat, continuing until the secondary facet is completely ground on both sides of the drill. When the secondary facets are completely ground, make a couple slow passes with no additional infeed to "spark out" the grinding and improve the finish.
Drills which have been hand sharpened often differ markedly between sides, requiring material be removed to get the sides equalized. A major difference in the heel area won't matter much but the complete lip area needs to show fresh grinding. When considerable material must be removed, check that the lips remain horizontal, adjust them back to horizontal if necessary and continue until at least the lip area is satisfactory.
When the secondary facets are completed, traverse the drill to the extreme right away from the wheel. Flip the secondary angle triangle forward and lower the trunnion table onto the primary relief eccentric. Traverse the drill slowly past the wheel and back, index 180 and traverse the other lip. Stop the motor, remove the chuck holder and verify the four facets meet properly in the center and the lip is sharp. A wire edge is common and can be removed with a slip stone or by scraping with an aluminum scrap. If the primary facets differ from one another check for a bent/damaged drill or swarf which prevents the collet from holding the drill properly.
To add SPA's, place the chuck holder onto the traverse table in the SPA holes (30 degrees on the drawing). Scootch the drill+chuck forward until the outer tip of the lip touches the wheel face; traverse as needed so they'll meet. The distance here is farther so it may take multiple scootches to get contact. As above, position the index ring about 1/10" from the chuck holder and in contact with the index pin then lock it to the chuck. Turn the infeed clockwise to contact the chuck holder, loosen the chuck lock and turn the infeed clockwise an additional 20 degrees and re-lock the chuck. It is more difficult to judge contact with the tip of the lip so it is better to err on the side of removing less metal since once removed you can't put it back.
Leave the trunnion table at the primary relief angle. Turn the motor on and traverse past the wheel, index 180 degrees and traverse again. Infeed and repeat until the desired SPA facet size is produced. For large SPAs, also grind the secondary relief. Turn the motor off and wait for the wheel to stop before removing the chuck holder - there isn't a lot of space so it's easy to ruin your sharpening effort by bumping it into a moving wheel. Alternatively, if you want to leave the motor running then loosen the chuck lock, slide the chuck back, lock it in place and remove the holder.
Procedure is different than a conical sharpener, a bit more complex because setup changes for the various facets but it isn't complicated when you understand the desired result.
Small Drills = 2 Facets
Drills smaller than 1/16" or so extending the normal 0.45" from the ER-20 collet may flex and vibrate when sharpening is attempted. This can cause the drill to "catch" on the wheel and break so it isn't a viable way to sharpen small drills. Small drills must be held closer to the point to avoid this problem but the ER-20 chuck then conflicts with the wheel when inclined to the secondary relief angle. Drills down to #60 can be sharpened by grinding only the primary facets, i.e. similar to standard sharpening. A primary relief of 15 degrees works if the extension from the collet is set at 0.170" or so. This allows sharpening small drills but requires care to avoid contact with the chuck nut - it clears the wheel by only 1/16" or so. The benefits of 4 facet sharpening are lost but it is possible to sharpen small drills acceptably with this approach. See an alternative method for small drills in the Addendum.
Snooze Interlock (Optional)
While modifying a drill from 118 to 135 degrees I dozed off: after examining progress I put it back in the 118 degree position and lost the progress I'd made. I then added a "snooze interlock" to prevent this in the future. I placed a ruler against the central side of the locating pins in the bottom of the chuck holder and marked a point 1" back from the center of the forward pin. This was drilled 0.2" deep with an "I" drill, enough to clear the head of a 4-40 screw. Similarly, the trunnion table was marked by laying a ruler along the right side of the index pin holes for the 118 and 135 degree positions and marking at 1" from the center of the forward hole. These marks were drilled and tapped 4-40.
A 4-40 screw is threaded into the appropriate hole in the trunnion table for the drill point angle being sharpened. The chuck holder fits just as it did previously except that if you attempt to place it in the wrong position it won't go. This was quick to do and eliminates this source of potential errors. (The snooze interlock screw is visible in Photo 9.)
Point Splitter (Optional)
Point splitting is a variation of web thinning that extends the cutting lips almost to the center of the drill face. Split point drills cut more efficiently (less heat generated) and require less thrust while drilling. Split point drills also have less tendency to walk at start of drilling but this is not generally an issue with 4 facet drills. Both split points and SPAs help to reduce wander when drilling deep holes. Unlike 4 facet sharpening, point splitting with this simple jig is more of an art form where some user judgment is needed for best results.
Point splitting is possible with a modest addition to this 4/6 facet sharpener. Based on Mazoff's document[1] I built a version to produce a "modified split point", similar to DIN 1412 C. This point splitter provides reasonable results considering its simplicity and that my wheel's corner is slightly rounded from use. 
The modified split is angled more than a regular split point and its edge is undercut to provide positive rake. Both of these features improve cutting action near the drill's center. Some aspects of this splitter (and the rounded corner on my wheel) conspire to limit it to drills larger than about 0.200". Fortunately, point splitting is most advantageous for these larger drills.
The 6 facet split point drill shown in Photo 7 is 21/64" with a 0.070" web, where I left a 0.018" wide point (point width is easily adjusted). Per Mazoff the point could be as small as 0.010" and remain strong enough (the rounded edge on my wheel limits this). The main benefits of split points on 4/6 facet drills are efficiency and thrust reduction, where narrowing the point beyond 20% of web thickness has a diminishing effect on thrust. The characteristics of the split point produced may be varied considerably by adjusting rotation angle, infeed, and point width. The unusual looking drill point shown here incorporates most of the capabilities of this sharpener.
My prototype point splitter is shown in Photo 8. It is made from a block of HDPE 1.45"x2.35"x1.73" cut to triangular shape per Figure 7, plus a piece of 1.5" aluminum angle 2.8" long. (Metal or other plastic would serve as well as HDPE for the triangle.) The front of the aluminum angle is positioned even with the front of the left trunnion table support and held in place with one 8-32 socket head screw. However, it is anticipated builders will use various motors so dimensions of the mount for the triangular block may differ from mine. The desired relationship between the wheel and the triangular block is described below so builders can construct a mount appropriate to their configuration.
The flute angle on drills is commonly 30 degrees so drill points are often split by grinding at that angle. This would require the drill extend farther from the ER-20 chuck than is desirable so a compromise of 35 degrees was used to reduce the extension to 1". The 1.5" height of the support for the triangular block plus the yellow pad was chosen so the drill point is about 1/2" below wheel center. The wheel curvature then provides the angle for the "modified split point" while the taper of the wheel undercuts it to provide rake. Other choices are possible, of course; e.g.raising the triangular block more would make the split angle steeper, closer to a standard split point. (In a more elaborate point splitter this height might be adjustable.) If the rake (undercut) is too steep the triangular block can be rotated clockwise (seen from above) to reduce rake.
The height of the front lower corner of the chuck holder's pad is 0.15" above the support so the chuck nut clears the support with some allowance for infeed. The distance between the wheel and the chuck nut is 0.10" measured at the point of the nut's hex, when the nut is set 1/16" from the chuck holder (to allow retracting the drill from the wheel slightly).
Photo 9 shows the optional point splitter mounted on the sharpener. It is secured to the trunnion table support by a single bolt so it can be removed easily if desired.
Point width is set using a tapered stop, seen near the right rear table bearing; blue tape marks the position for 20 thou point width. Sliding this stop farther out from under the traverse table narrows the drill point. This stop is removed to change from point splitting to sharpening mode. The socket head screw in the traverse table, just left of the taper, contacts the taper to provide the stop. There is another socket head screw in the mounting plate under the table to ensure the taper can't swivel. When the taper is removed the screw in the table can pass between the bearing and this screw in the mounting plate. The stop is a scrap of 1/8" steel 4" long, tapered about 15 thou per inch.
The tool made earlier to set the drill extension to 0.45" is modified by adding a similar flat bottom hole on the other end 1" deep. This, of course, is used to set the drill extension for point splitting.
The index/infeed ring needs a witness mark to set the rotation angle for point splitting. This angle should be 35-40 degrees but can be changed based on experience. To add a witness mark, place a fairly large drill in the chuck with the lips horizontal. Rotate the index ring clockwise against the stop and lock the index ring to the chuck. Rotate the drill 40 degrees using a protractor to judge and add a small dot of ink on the index ring, just in back of the index pin. Some experimenting with this angle may be needed based on the height you choose for the drill point vs the wheel and the infeed and point width. Once you settle on a setup, scribe a permanent reference mark for the rotation angle.
The initial setup for point splitting is: set the drill extension to 1" using the tool made earlier. With the lips horizontal, set the chuck nut 1/16" from the collet holder; use a spacer to accurately set this. Lock the chuck, retract the infeed screw completely, rotate the index ring clockwise against the index pin and then CCW until the ink dot is just aft of the index pin. Hold the index ring tight against the chuck holder, lock the index ring to the chuck, release the chuck lock, rotate the drill CW to the stop and lock the chuck.
Aligning the Point Splitter
Alignment of the point splitter is more challenging than aligning the 4 facet sharpener because it relies on user judgment rather than objective criteria like the test pin used earlier. In addition, the adjustments interact somewhat so small adjustments are made and evaluated repeatedly to "walk" them to the desired setting.
A test drill of 3/8" to 1/2" is needed for alignment; if a mis-step occurs during alignment this drill may wind up being sharpened repeatedly. A 10x magnifier may be helpful in examining the drill point as you proceed. Begin by sharpening this test drill, ensuring the facets meet precisely -- this meeting point will be used as a reference for aligning the split.
The goal of alignment is to accurately set the infeed such that the flats which form the split point approach the drill point with appropriate depth so there is a slight undercut left in the area of web forming the split. The first approximation is to use the initial setup for point splitting described above. Traverse the table full left; the taper stop isn't calibrated yet so use care during calibration to avoid grinding too far, damaging the drill tip. Place the collet holder onto the triangle and traverse to approach the wheel. From the left side, look parallel to the wheel past the point of the drill. The drill should have its point barely past the wheel face. Adjust the infeed to achieve the desired relationship as best you can judge. This may require scootching.
Back the infeed out so the heel of the drill just grazes the wheel. Turn the wheel on, grind the heel and about 2/3 of the way to the drill center, index and grind the other side. Infeed 3-5 thou, and repeat. Look along the flat produced to see where its extension passes the drill point. If this extended line passes to the left of the drill point, repeat the infeed/grind/evaluate cycle until the line extension hits the drill point. If your wheel's corner is a bit rounded, as mine is, use the outer part of the flat to decide when you've ground enough. In Photo 7, this line passes a bit to the right of the drill point but this resulted in excess rake causing the split's edge to chip in use. I kept this picture only because the lighting was the best in any of my drill point shots.
Carefully enlarge the flats toward the drill center but avoid grinding the primary facet at this stage. Look at the flats and decide whether extending the flats will produce a small positive rake on the split point when the grind is extended further toward the drill center. Padding under the triangular block and/or rotating the triangular block allows further adjustment of the rake and split angle.
With the grinder off, adjust the width of the taper stop so when set at its mid point it stops the traverse at the point found above, just prior to extending the split into the primary facet.
Using the taper stop to control the point width, grind the split farther in small increments until you judge the split point acceptable (this may be limited by a rounded wheel corner). If necessary, reduce the width of the taper stop further to allow achieving the desired point width. Add a witness mark to the taper stop indicating this width. With a little practice it is possible to judge how the taper stop position relative to the witness mark will affect the split point.
It is important to be able to reproduce the drill infeed position which provided the above result. One way is to measure the gap between the chuck nut and the chuck holder and make a spacer of this thickness. A convenient method is to thin the narrow end of the taper for use as the spacer, saves having to keep track of another tool. Setting the infeed position with a spacer gets it close but isn't precise because the collet position can vary several thou based on the amount of compression needed to grip an item. If more precision is desired, use the drill as positioned here to set the distance to the plexiglass in a lip alignment jig similar to the one described later. Or make a combined jig with two positions.
Further tuning is possible to adjust the split produced. Infeed, drill rotation, and point width adjustments allow considerable variation. In addition, raising the triangular block with a pad will increase the angle of the split, rotating the triangular block can change the rake angle. The basic setup will get things close but all of these adjustments interact somewhat so it comes back to user judgement and experimenting to arrive at a setting that works well.
Using the Point Splitter
The basic setup described above should produce good results; a bit of experimenting may allow improvement. The following is the basic procedure I use.
Traverse the table to the extreme left position and insert the taper stop fully, to produce maximum point width.
Install the collet and insert the drill, leaving over an inch extending. Tighten the collet finger tight, then use the tool to set the drill extension to 1" and tighten the collet. Set the lips horizontal plus use the spacer between the chuck nut and the chuck holder to set the overall drill position. Lock the chuck, back the infeed out all the way, rotate the index ring clockwise against the stop and then back CCW to the angle mark. Lock the index ring to the chuck, loosen the chuck lock, rotate the chuck CW to put the index ring against the stop and tighten the chuck lock.
Most of the material to be removed is on the heel of the drill. Loosen the chuck lock and use the infeed to back the drill away from the wheel so this material can be removed using several shallow grinds, then tighten the chuck lock.
Install the chuck holder onto the triangular holder, positioned by the index pins. The drill should be to the left of the wheel and well clear of the wheel.
Turn the motor on. Secure the chuck holder to the triangle with finger pressure and gently traverse the drill to the right. Traverse only about 1/2 of the way to the drill point. With the infeed backed off the drill point is higher up on the wheel and the wheel curve is such that the point could be damaged if traversed too far prior to full infeed. Rotate the chuck 180 degrees and grind the other side similarly. Advance the infeed and repeat until you're back at the original set point (infeed backed out all the way). Once at full forward position, traverse to the stop on each side sequentially. Dwell time at the stop can affect the amount ground very slightly so try to time both sides similarly. Traverse fully left, remove the chuck holder, and examine the point. Since the taper stop is at the maximum point width position the point is not fully ground yet. Examine the point and adjust infeed if needed; make additional passes as necessary.
Adjust the stop to set the desired point width and finish grinding the split point. This can be done incrementally by taking small amounts if desired (a good approach while getting used to the unit). Examine the split for symmetry and dwell a bit longer on one side to improve symmetry if needed.
As noted earlier, point splitting with this jig is a bit of an art form because it requires that the user evaluate and adjust as the process goes along. The jig makes it easy to adjust the split depth and to improve symmetry -- the rest is up to the user's judgment.
Drill Lip Alignment Jig (Optional)
Setting the drill lips horizontal is easy for large drills but becomes more challenging for small drills. The jig shown in Photo 10 helps to quickly align the lips horizontal and can also set the amount the drill protrudes so "scootching" is minimized.
I used a scrap of aluminum channel but any flat bit of metal should work. Add holes spaced to fit the chuck holder. Put a drill in the collet holder and set it up to touch the wheel as described earlier for use in calibrating this jig. I used 1/8" plexiglass 1" wide for the alignment plate, height set just below the middle of the drill. Bolt this to a small block of metal as shown. Position this so the plexiglass just touches the end of the drill (to allow setting the chuck forward position using the jig) and bolt the block in place.
In use, the horizontal edge just below the drill lip provides a reference for setting the lip accurately horizontal; a magnifying glass is helpful for small drills. And by moving the chuck forward in the holder until it almost touches the plastic reference then locking the chuck, the index ring can be set so when transferred to the trunnion table it is ready to be sharpened (with no scootching).
4/6/8 Facet Examples
The drill point in Photo 7 illustrates all of the capabilities of this sharpener. The examples here show some subsets of the overall possibilities.
I used drills found at flea markets for much of my testing while developing this sharpener. The 5/16" drill in Photo 11 had lived a hard life and been resharpened several times previously. It was likely a split point originally, as evidenced by the heel area grind marks. By eye this 4 facet resharpening looks good but little details show up when viewed under my microscope. Here, a wire edge left by grinding is visible on the edge of the near lip. The wire edge can be removed with a slip stone. The curved junction between primary and secondary facets shows clearly, the result of my rubber motor mount.
The 11/32" drill shown in Photo 12 has small SPA's added making it 6 facet. These extra facets cause the drill to have a stronger self centering action and the sharp outer point on the cutting lip is eliminated so the drill remains sharp longer. The chip is weakened by the difference in cutting action between the primary and SPA facets so long spirals are less common because the chips are prone to break. I haven't seen much difference in hole finish from shearing action except when enlarging a hole by a modest amount. When through drilling the SPA reduces or eliminates the exit burr on most materials. It requires only one additional hole in the trunnion table to produce SPA's, where size of the facet is set by eye; facet size isn't critical so simplicity won out. Secondary relief can be added to the SPA but isn't necessary for small SPAs.
Note the slight curve in the junction between the primary and secondary facets; this is because the (free) motor I used has a rubber mount so it moves away from the drill slightly when grinding the widest part of the secondary relief facet. A rigid mount and a ball bearing motor could eliminate this but it doesn't affect the way the drills cut so again simplicity and cost carried the day.
As mentioned earlier, it is easy to experiment with the drill point and associated relief angles using this sharpener. It's possible to get carried away in the process and go too far, resulting in poor performance. Photo 13 shows an 8 facet drill with large SPAs, so large that secondary relief was needed for the SPA -- and even that wasn't enough. This drill was tested by drilling several holes in 1/2" mild steel, which produced heat discoloration in the heel area from rubbing. Hand grinding this area could eliminate this contact but instead I use smaller SPAs since they increase drill life without the hassle of hand tweaking the heel. There is also slight heat discoloration seen at the center; this is typical when drills extrude the center material rather than cutting it - a pilot hole would avoid this. Alternatively, split points cut almost to the center so they eliminate or greatly reduce both of these issues while also reducing required thrust.
Further Thoughts
Many aspects of drill sharpening are surprisingly forgiving if the drill lips are symmetrical and relief is appropriate. This design attempts to address symmetry and relief while allowing some flexibility to tailor a drill for specific tasks. It is fairly difficult to botch sharpening if the drill is put into the collet correctly. A modest error in setting the lips horizontal generally won't affect drill performance - the sharpener will ensure symmetry (although the primary facet may look unusual). Primary relief allows tuning for improved performance but most any value 7 degrees or larger will work. Secondary relief just works at the default value. SPAs can improve drill performance or, as noted above, can degrade performance if too large so work your way up in SPA size. Split points reduce thrust needed for drilling dramatically, especially helpful for large drills. This unit is useful as a drill sharpener and also as a gadget to experiment with and optimize performance of drills.
Small drills sometimes break in use. Grind the broken end flat on a bench grinder to simplify setting the lips horizontal. Then make a pass with the sharpener; check and re-adjust the lips horizontal (if needed) and complete sharpening. Large drills that are broken should be ground to approximate shape, then completed in the sharpener.
I often use #1 center drills for starting holes but find them relatively fragile. When the tips snap off they can be re-sharpened to resemble a spotting drill (but 135 degree with 4 facets) -- and are much less fragile than they were originally. Spotting drills should have a larger point angle than the drill to follow, i.e. use a 135 spotting drill followed by a 118 degree drill. If you commonly use 135 degree drills, add another hole to the sharpener for 144 degree spotting drills. If the following drill has the same or larger point angle than the spotting drill, one lip will often touch first setting off chatter until the drill engages the work. This can displace the hole and/or chip the drill, especially with carbide drills.
A sub-goal in this design was to make it easy to work on. Each major section was to be separable from the rest by removing at most two screws. This went well until I added the traverse lever and the ball bearing - three screws must be removed to get the traverse table off (the bearing slips by). It's still easy to work on but I didn't quite make the two screws goal.
Bill of Materials
Most material can be adapted from items found in a typical home shop so feel free to use what's on hand. Material for optional items is not listed.
- 3.625 x 3.625 x 0.125 steel, Trunnion table
- 4.25 x 5.5 x 0.125 steel, Traverse table
- 1 x 3/8 x 6 steel, trunnion holders, traverse table support
- 1 x 1/2 x 10 steel, trunnion supports
- 2.5 x 1.2 x 1.3 steel, Holder for collet chuck
- 2.95 x 1.2 x 0.375 steel, pad for chuck holder
- 1.5 Dia, 1/4" long steel, for primary relief eccentric
- 0.125 drill rod, for locating pins
- 0.250-0.375 rod, drill rod (or from dead line printer), for trunnions and alignment tools
- 0.625-0.75 round, 2" long, for tool to set drill extension
- 0.25-0.312 brass round, for lock screws
- HDPE for traverse bearings
- Felt cloth for trunnion washers
- Small sealed ball bearing, for traverse (e.g. R-1350ZZ from a dead VCR)
- Motor and wheel
- Mounting plate for traverse table and motor
- Base to hold unit
Purchased Items
- ER-20 collet chuck, 1" OD, 4" shank (CTC Part# F95)
- ER-20 collet set, metric 0.5-13mm
- Wheel, 3.5" CBN or diamond, flaring cup, 11V9 form. Grit 150-300
- Fasteners (Substitute freely with next larger size, i.e. 6-32 replaces 4-40 etc. if space permits)
- 6-32 x 1/2 socket head screws, 6ea for trunnion holder and trunnion pins
- 6-32 x 1.25 socket head screw, 1 ea for infeed
- 8-32 x 1/2 socket head screws
- 4-40 x 3/8 phillips screws
- 4-40 x 1/2 phillips screws, 2ea for chuck holder pad
- 4-40 x 5/8 phillips oval head screws, 4ea for traverse bearings
- 4-40 x 5/8 phillips screws, 1ea for traverse ball bearing
References:
- Mazoff, Joseph; "Drill Point Geometry", Google search
- Brown, D.A.G.; "Sharpening Small Drills", Model Engineer, January+February 1993
- Bradley, Ian; "For Honing Small Drills", Model Engineer, November 1961
- Moltrecht, Karl; "Machine Shop Practice - Volume 1"
Submitted by:
John Moran aka GadgetBuilder
8 Newfield Lane
Newtown, CT 06470
Email: John@GadgetBuilder.com
My original infeed screw used an Allen wrench for adjustments. I made an extended infeed screw with a spring soldered in the middle so it wouldn't be easily damaged. Works well, makes infeed adjustment more convenient. 
