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

[Witold Grabiec]

I'm gonna have to disagree with flip-it-over suggestions. While you can get it done this way, you may need a few more boards to get it right. Unless you make a jig that will register your board in exactly same spot on either side. Your small hole is not a good enough guidence to rely on it. I know your cut does not need to be perfect, but since you seem concerned with the quality, use the backing board, which will ALWAYS give you a nice clean cut if used properly.

As for the speed of rotation, you cannot go too slow with a Forstner bit, in fact any bit except a hole saw. Your speed must be matched to material. The softer the material the faster the rotation so as to prevent tear-out on entry.

[Bill Laidley]

Jeez guys... I don't know if we aren't making this too difficult. I can find something to agree with in most of the replies - but I can also find something to disagree with in most of the replies.

Flipping the board: yes this works to reduce chipping. Is there a chance of misalignment? Yes. Is the misalignment significant? That depends on how careful you are.

Using a backing board: this also works to reduce chipping. Is there a chance that it will still chip? Yes. Two things will help - clamping the lens board tightly onto the backing board, but more importantly make sure the drill bit is sharp and properly ground. You decide if a bargain priced forstner bit is apt to be really sharp and properly ground. It also helps for the bit to be turning at the right speed.

Gawd, if we want to get really obsessive we'd could buy $15,000 pin routers, make a set of jigs and have perfect holes in our lens boards.

Aren't we supposed to be taking pictures?

[Nick_3536]

Alignment is simple. I clamp two pieces of wood [about 1"x1" long enough to span the drill press table] The lensboard goes between these two. If you're drilling the middle of the board then flipping the board won't be a problem. The board can only move between those two boards. It's fairly simple to align things.

Who makes cheap large forstner bits? All the cheap sets I've seen max out at about 1". Other then the odd 3" clock bits anything over 1" tends to force you to get better bits.

You could try masking tape on the back of the board.

Big bits == slow speeds.

[John Kasaian]

Nick,

The set my local Costco is selling is called Mastergrip with sizes from 1/4" to 2-1/8" going for about $35 bucks.

I just drilled the "C" board after building a jig to register the piece and flipping the board over halfway through the drilling---no splintering! The registration is just a hair off, but I undersized by 1/16th, so when I sand it down to fit the lens it should be looking good.

Thanks for all the suggestions!

[Bill Laidley]

Okay, to give you a price comparison: Lee Valley (Canadian woodworking tools company) sells a set of 29 bits from 1/4" to 3 1/8" (technically the bits are forstners from 1/4" to 1", and saw tooth above the 1" size) for $249.00 CAD (high carbon steel) or $329.00 CAD (high speed steel). They aren't the cheapest or most expensive place on the planet, but the quality is good.

[RichSBV]

I can vouch for the "cheap" Forstners. They work well but may not stay sharp for very long. I have cut several boards with them on a drill press with no problems. Even quickies in cheap plywood. Simply clamping the board onto another board takes care of most of the splintering as has been said.

But I would like to make a recommendation. I have had to cut a few where the Forstners either weren't the right size or I didn't have a large enough one. For those, I use a circle cutter in the drill press. Adjustabe to any size and easily set accuarately with a caliper. Cuts a hole as well as a bit and will even do aluminum boards with a slow speed and light pressure. Well worth the minimal investment! Just be very careful when using one!

[tim o'brien]

I prefer the hole cutting bits from Milwaukee, slightly undersized, turn over the board before you go all the way through with the outer cutter, finish it off then take the lensboard and chuck it on my lathe. Using a sharp chisel and sand paper, I can get the hole perfectly centered, clean and pefectly sized for the lens in question. It also allows me to put in stepped edges if required for those hard to fit locking rings. Coat of flat black on the back, coat of polyurathane on the front, and voilla!

tim in san jose