I just finished a small folder with gold-lip pearl scales, useing 1-72 allen head screws with very small heads to secure the scales to the liners. Despite useing new cobalt drill bits, taping the finished side, and useing plenty of water, I've got slight checking around the edges of the screw holes. It's so slight that I doubt that anyone would notice without 2X+ magnification, but it's not what I had wanted.
I can probably chamfer and polish these edges to a uniform contour, but had hoped to obtain a perfectly flush fit with the screws (1-72's with very small allen heads filed flush).
Any suggestions on how to get the holes pefect on the next one?

For what it's worth, I had picked up a "reamer for precision holes" from Texas Knife a little while back. Used it on the screw holes of that Tiger Coral knife and it worked real well.

I've been sitting on a nice set of MOP scales for a few weeks. Looking forward to seeing yours pics and hearing details, prior to starting up on mine.

Dennis

Kelly, the problem you describe is complicated by a number of factors.

First, you are talking about gold lip pearl. The characteristic color of this pearl is on the out or finished side of this material, which limits your ability to remove chipping by grinding down the exterior.

Second, I am assuming you are talking about a counterbored hole.

For straight holes, a solid backing, light drill pressure, and a few drops of mineral spirits seems to address most problems that occur when the drill breaks through the back. With a counterbore, however, you are not concerned with chipout on exit, since the drill stops short of going through the piece.

I have never had a problem with hole deformation or chippping on the entrance side of the hole. I do use carbide drills, but have used cobalt (and even HSS) with good results. I am mystified at the cause of your difficulty.

Sorry I wasn't clearer - For the primary screw hole, I drilled first through the back of the scale with the front (finish) side taped; then I drilled the counterbore for the screw head right through the protective tape on the front side, and kept the surface area and drill bit wet with water during the process.
I'm not sure of the speed of the drill press - for these holes I used my Grizzly mini-mill with a variable speed control at about 50% its rpm capacity, probably around 3,000 rpm's.
Best guess is that the chipping occured when the bit just entered the pearl to its full diameter.
I'll try mineral oil and carbide bits next time and see if that's better. What do you find to be the best speed for drilling pearl?
Thanks,
Kelly

Slower is generally best, even with small diameter drill bits. If it were me, I'd skip the tape. It appears that it didn't help when you drilled your primary hole (from the inside to the outside); I'd bet that the chipping occurred then rather than when you started your counterbore.

Instead of the tape, place the (flat) pearl blank on a piece of micarta, diamondwood, or some other (flat) substrate before drilling. You could even use your tape to hold the pearl securely to the backing, but not in the area where you will be drilling.

Use the lightest of feeds when the drill is close to breaking through the pearl, since this is when most chipping or cratering occurs.