Acoustic Guitar Construction

OK, I'm trying to hone my binding skills and find the "right" setup for me. I tried the IA attachment but my hand seemed too unsteady and the channels were, well let's just say uneven. I bought a tower setup and it works fine except for one thing. I get spot on widths both binding and purfling channel however, on the back as the donut rides up the radius it changes the depth of the channel i.e. if it is set for .250 in spots it is only .225 because of the rise. What is the cure for this?

Donut too big.

Donut angle too shallow.

Donut flat too big a diameter.

Or all of the above.

Might be all 3. Can you tell from the pics? The thickness is 3/16". What dimensions should I shoot for. This is the second one I made the first one didn't have a large enough flat spot and did lift over the purfling channel and routed the binding channel too deep.

Forgive me, I am not understanding how that bit works without having a bearing to gage the width of cut?

Sorry I just took the bearing off when I was done with the routing. Different size bearing for different widths.

Mine only rides on the ledge of the guitar about 1/4"; the flat area, then it tapers away quickly, but the whole think is only about 3/4" larger around then the hole for the bit. This works perfect.

Kevin

I know its evil but why not get one from Stew Mac measure and return? But yes I also was thinking its too large.