I use #16 Exacto blades to scribe around the bridge and they work for me. I haven't had the tiny chips in the finish you mentioned. What finish are you using?

The one pitfall I had early on was not getting the corners of the wings fully cleaned up. Be sure the ledge is not hanging up on a piece of finish.

I find I prefer the results I get with a very sharp violin knife compared to the disposable scalpel blades I’d used in the past. In repairland we are, often, dealing with cheaper instruments with horribly thick finishes and the rigid violin knife cuts deep through the slab of poly with authority where the whippy scalpel blade may deviate if appropriate care is not taken. I just find the violin knife easier to control and of course I’m in charge of bevel angle too since I’m the guy sharpening it, can run single or double bevel, and I have knives set up in both configurations. Of course there is a trade off in time spent sharpening/lower cost vs quickly grabbing a fresh disposable blade but having another consumable to keep in stock.

If you are cutting lacquer and getting a chippy edge I’d suggest that either knife is not sharp enough, blade geometry is wrong for the task or perhaps alter your technique. It should be possible to knife a clean edge through a few thou of nitro, especially fresh nitro on a new build and Behlens/Mohawk stringed instrument lacquer is pretty soft as a fresh coating compared to some other nitros. Apologies if I’m stating the obvious but you would take the cut gradually in several passes with an exacto, the first pass an extremely light scoring, the next pass a little heavier to deepen it etc. Chipping suggests to me maybe pushing with a little too much force?

Karl, are you set on clearing the full footprint? What many folks do is remove a reduced outline of the footprint, maybe 1/32 or so reduced, and then cut a rabbet around the perimeter of the bridge so that it sits on top of the finish around the edges?

Some pics of the job and the jig I use are below. I first learned this here from Colin North I think was the first one to show the jig.

I use the 3M 06528 tape to mask the bridge footprint and fretboard extension footprint. I have also used frisket film which is a little thinner than the 3M tape.

I use an xacto to cut the tape out which gives a good edge but since the footprint is reduced it doesn’t have to be perfect. One tip about the xacto that could help, the first pass flip the blade around and scribe with the backside of the point. Do this lightly. The blade has less of a chance to wander when used reversed this way and subsequent passes will follow the first pass pathway. Dave Farmer shared this with me and it works really well.













Brad


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Is this what you are asking about?
https://www.stewmac.com/luthier-tools-and-supplies/tools-by-job/tools-for-binding/precision-router-base/precision-router-edge-guide/
The one I used myself was a Laminate Trimmer Guide Assembly which came with one I bought - a Makita 700 series or Bosch Colt IIRC.

Yep, that’s it.

You flip this part upside down:


And put a radius dome platform (the MDF) and a riser (the 1/2” birch ply) between the guide and the dremel base:





Does that help?

Brad


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