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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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Cambrian Guitars

"There goes Mister Tic-Tac out the back with some bric-brac from the knick-knack rack"

Very nice. I'd give you a whole page of those clappy emoticons if I were into that sort of thing

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I resemble that remark.....

Dave my friend this is too cool!!!!! If I could purchase one I most certainly would!

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Ann Arbor Guitars

That is just too cool. What a concept.

Brilliant!

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"After forty-nine years of violin building, I have decided that the search for a varnish is similar to the fox hunt. The fun is in the hunt."
Jack Batts Maker and Repairer of Fine Violins

You read my mind, I'm in the process of attaching a 1/64" scale to my StewMac Rosette Channel Cutter, I thought it needed to be more accurate. I may pause my progress and adopt your method. Cool!

Glad it interested a few people at least. Joe, please post piccies of your conversion when you get it done.

I may re-design the whole base/dremel holder using laser-cut acrylic and incorporate a better digital scale (that reads radius directly - center of router bit to center of circle) into it....we'll see - depends on how much free time I can treat myself to in the next few weeks.

Cheers,
Dave F.

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Cambrian Guitars

"There goes Mister Tic-Tac out the back with some bric-brac from the knick-knack rack"

Very cool.

As a tip, I don't think you annealed it when you heated and then quenched it. I believe you hardened it. I may be wrong regarding stainless, but with high carbon steels you anneal by heating very hot then allowing to cool slowly. The slower the better.

Darrin

I just did some quick internet research, and it seems like the process for annealing stainless is backwards( hot -> quench = anneal), and that stainless is only hardenable by work hardening. Cool, something new everyday.

Really cool mod Dave F.!

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Jordan Aceto
Ithaca, NY

I watched a DIY network video on Lynn Dudenbostel making mandos or guitars. I showing a dial indicator (not caliper...) on his. Not sure how it was mounted, but it's easy enough to do

Jordan:

I just looked too. Like you said, learn something new. Weird that it is backwards. I would have never thought that. I stand corrected Dave, you were right on the money from the get-go.

Darrin

Great job Dave, and very innovative!

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Thanks,
Blain

http://www.ullrichguitar.com

"89.67% of all statistics are made up on the spot."

There's also a special oil you can use to quick cool steel to put a less brittle finish to the steel. My dad was a tool&die maker and used to show me the various tool finishes based upon how he hardened them. Remember hardened steel is hardened on the surface, the interior is not as hard because it cooled slower. I think there are also water treatments you can use to create different surface hardness. I was facinated as a kid to learn my dad could make a piece of steel too hard to machine, then make it soft again to machine it again. Also all this heating and cooling changes the size of the object. Of course it's in the thousandths, but still, might matter, it did to him.

To put pulleys on shafts, and also in other tool-holding applications, they make use of that. On the Fadal the pulley that spins the spindle is put on that way; to take it off you need to heat it up with a torch.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services