Forstner drill bits for drilling lensboards? A tour d' forstner or just another boring story?

Hello! My 3 year old son and I went to Costco the other day and came home with a nifty set of umpteen forstner drill bits in sizes that looked useful for drilling lensboards, all in a fitted plastic case that reminded me of Sean Connery's attache case in 'From Russia, With Love.' I chucked one of those bits into the drill press and centered an old Agfa board over some scrap lumber, clamped the whole she-bang down and went to town, drilling from the face of the lensboard. It produced a nice clean hole ever so slightly undersized so a little light sanding should suffice to clear the lip of the flange so I can mount my 14" Artar. After turning the board over though, wooden you know it, the Forstner bit had raised some splinters on the painted side of the lensboard. Harmless, and a little black paint should make it look nicer, but I've seen other lensboards with the same crude splintering. Is this a forstner kind of a thing or is it on account of trying to drill an old piece of joinery? Any recommendations to keep it from happening again when I drill a much thinner Graflex "C" board to mount a 203 Ektar?

You could try clamping the board tightly to a backing board. Generally this helps with tear-out on a drill press. Use the slowest speed on the drill press and go easy.

Hi John... The backing board can help a lot.

When drilling the hole in a door to install a doorknob, carpenters will stop drilling as soon as the small 'centering point' of the bit comes through the opposite side of the door... then use that small hole as a guide to finish drilling from the opposite side. I hope this simple description helps.

I've found that a hole saw bit in a drill press also works well. I drilled an aluminum lens board this way. It still needed a little touch up with a file on the inside to remove the burr left by the bit.

I think that with the bit you used, a good tight fit to a backing board is necessary and I'd try faster rpm on the bit, with a slow feed. Some experimenting will be in order to find the best speed.

As the others have suggested, clamping the board firmly to the backing is the key. I made several wooden lensboards for an old Linhof Tech II this way using a keyhole saw and I used three clamps to hold down the board and didn't have any splintering. A Forstner bit should be even cleaner.

Dee suggested a faster RPM. I would note if you to this to be very careful. Large bits such as these have a very high rim speed and overhead extremely easily; consider the rim speed of a 1/4" bit and a 2" bit at the same RPM and you will begin to see where the problem is. If they overheat bad enough to blue the edges, temper can be ruined and the bit will not hold an edge.

I agree with Paul, speed must be matched to bit size. It must be fast enough to provide a clean cut, yet slow enough to prevent the burn. Speed at which you feed the bit through place a role in here as well. As others have said, a back board is the only way to get a clean exit cut. In order to get best cut on both sides, you can sandwich your lens board between two other (all you need is a 1/4" plywood) and this will also ensure a perfect entry cut as well (drill a small center hole in the board and another in the top sandwich piece to guide you through).

Just a small observation that you don't absolutely have to use a backing board. Drill partially in on one side, flip the piece over and drill the rest of the way from the other side (same idea as the precutting often used to prevent splintering veneer laminates on table saws). This requires more alignment and more time than using a backing board, but is sometimes a better approach. When the web in the middle between the two bores gets thin, it will tear out (doesn't matter what kind of bit you use, though I prefer hole saws), but this seldom damages the part unless you're drilling dry, brittle wood. Even then you can usually get a clean hole by feeding very slowly when the web's about to break.

If the bit is the right size, and the lensboard material soft enough to use it on, go with it. My personal favorite is an adjustable fly cutter; requires a drill press that can go quite slowly, and the usual stuff about anchoring the board to the table. You definitely don't want to be hanging onto a lens board by hand when using a fly cutter to drill...

Regarding the suggestion for using faster RPM, let your insurance coverage be your guide. Use slow speeds for large holes, esp. in aluminum. If you're using a bit that punches through the center first (includes fly cutters and most Forstner bits) then as soon as the center pokes through, you can reverse the lensboard and finish the hole from the other side, no ragged edges that way.