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Is there an arbitrary bevel angle for a UHMW donut, or does it just need to clear the top and back radius with a small flat bearing point that rides on the edge? I'm using 28'R and 15'R for top and back.

Thanks, folks!

Alex

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"Indecision is the key to flexibility" .... Bumper sticker

The donuts I had were both more like the latter. There was about an 1/8" wide flat spot that it rode on, and then the edges beveled up around, I don't know, 10° or so?

I made my own. About 1/8" shoulder and the angle is arbitrary. I think mine is probably 30+/-*

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I made mine about 1 mm at the shoulder, figured smaller is better as the depth registration is then as close to the edge of the guitar as possible.
Bevel is around 25/30? degrees - enough so it doesn't ride on the the dome anywhere.
The point to watch for is the back, at the heel end.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I don't use a tower or the donuts -- but shouldn't the ledge portion be wide enough to accommodate the second pass for the purfling? Guess I am not seeing something, but if the flat ledge is only .039" (1mm) wide and a channel for the binding say, .075" has been cut where is the edge of the guitar resting during the purfling cut?

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Ken Cierp

http://www.kennethmichaelguitars.com/

The above all assumes the use of the LMI or Stew Mac (or similar) rabbit bit with bearing guide. The bit is a set size and the donut is larger than the bit. The ledge accounts for the bit size.

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The LMII design addresses my concerns -- I would want to make sure that the doughnut is riding on the "uncut" surface of the plates, if the router slips off that prime surface into a previously cut channel a mess could occur. The way I see it, the bearing guided bits prevent errors in the width of cut its the doughnut ledge surface that controls "height/depth" of cut. Check out the how to use video.

http://www.lmii.com/products/shopbrowse ... ry_id=1414

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Ken Cierp

http://www.kennethmichaelguitars.com/

As you switch to a smaller bearing, The cutter AND donut move in towards the center of the guitar.

Cool new micro adjust on the lmi!

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Pat

My evolution of binding jigs: LuthierTool jig > Williams jig > new LMI jig > Kett style jig.

I haven't used my Kett style yet, but I'm looking forward to it. I wanted something small and fast. The new LMI jig is great and felt the best to me; I preferred moving the guitar into the cutter rather than moving the cutter around the guitar. I just didn't like setting up the cradle.

Nice looking tool the LMI jig. But what happens along the back radius say for a tight Florentine cutaway? That wide ledge on the "donut" of the LMI jig will actually raise the entire router higher then the rest of the binding ledge around the lower bout area. A smaller or narrower ledge reduces this greatly.

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It was beveled just like the donuts, but there wasn't a distinct transition from the flat to the bevel. The two surfaces flowed/blended into one another. Like a real donut, I suppose