Hi Folks,
As you may have noticed by now, I'm an accuracy-a-holic when it comes to woodworking. I like to be able to dial in measurements to 1 mil or better. I also like the repeatability and time saving aspects of having digital readouts on my tools and jigs. The one guitar making operation that has irked me since I started making them has been routing the rosette channel. Early on I bought a Stewmac jig for my Dremel and eyeballed the radius measurements using a digital caliper held up to it, however I was never happy with guessing the center of the pivot pin and edge/center of the router bit. Don't get me wrong, I had good success with this eyeball method, but I always felt it could be improved.
This weekend, I finally did something about it. I purchased a new 6" digital caliper (one with absolute position, not one of the newer cheapy ones that resets to zero everytime you turn it on!) and went to it. I decided that with a few bits hacked off, it would fit nicely on the side of the Stewmac jig, parallel to the sliding deck, requiring only two screws to fit it.
Right-click the photos to see/download the high resolution version.
Here's the digital caliper I purchased for the task:
The caliper was completely disassembled - four screws in the bottom allowed the LCD/battery/plastic part to be removed in one lump. The long depth guage rod was easily broken off at the weld. Here's the two main metal parts marked ready for cutting:
The caliper is made from super-tough hardened stainless steel. I had to use an angle grinder to cut the excess bits off - it made a bit of a mess, but got the job done. In order to drill the two 1/8" holes needed to mount it, I had to anneal the stainless steel first, and in order to do that, I had to carefully remove the stick-on measuring strip to prevent it from getting burned up. Even after annealing (heat to cherry red, then quench fast in water), it took over a half-hour to drill the two holes! Here's the caliper reassembled and ready to fit to the Stewmac jig:
I marked the hole positions on the Stewmac jig and then disassembled it so that I could easily drill and tap the two new holes. I used a #40 drill and 3mm tap for these. Here's the jig, all done and reassembled, ready for use:
It works great! Of course, you still have to do some basic math to ensure you're routing in the right place, but now it's super-accurate and very repeatable! Maybe some enterprising person (with more time on their hands than me) should get one of the digital caliper companies to make a version that fits properly and sell it, or maybe Stewmac can adopt/adapt the idea.
Cheers,
Dave F.
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