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Depth Feeler

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My Depth Tool and a Starrett Depth Gauge (Click to enlarge)

The Starrett depth gauge works well and is an attractive tool with its color case hardening and nicely engraved scale with 1/64" divisions. However I seem to frequently need to find the depth of holes less than 3/16", where the Starrett won't fit into the hole. I generally held a small drill in my fingers and pushed it into the hole, comparing that to the desired depth - crude, quick, and not very precise. Each time I did this I thought about making a tool for this but put it off due to the effort needed to make the tool vs the number of times it would be used.

When I finally got around to making a depth tool it turned out to be trivial. My original (non-trivial) plan was to make a pin vise, similar to those used with the 4 facet small drill sharpener, the idea being that the pin vise would provide the friction to hold the pin while allowing it to slide nicely. I started by drilling a 0.063" hole axially through a 2.5" long piece of 3/8" line printer rod. This hole was drilled about half way through from each end. The drill drifted slightly so the holes didn't meet precisely - this prevented the 0.059" steel wire from going through. So I drilled the hole from the back one size larger and a bit more than half way through. This allowed the wire to pass through but provided some friction. No need for a pin vise to provide friction, just bend the wire slightly to adjust the amount of friction. Just like that, the tool was working. Only two parts, the body and the wire so it couldn't get much simpler.

I knurled the back end of the body although the tool would work even if the wire were inserted from the other end. The loop on the end of the wire is larger than the body to prevent the tool from rolling when it is laid on the bench. And the loop allows it to be hung near the lathe for easy access.

In use, the wire is pushed through the body until the loop contacts the body. Holding the body, the end of the wire is then pushed into the hole whose depth is to be measured until the body contacts the work. The wire extension from the body can be used along side the work to judge depth or can be measured with a ruler or caliper.

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