Drilling holes with a Forstner bit

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Knot Competent

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I need to drill some 32mm diameter holes through American Oak, at an angle of 45 degrees. I've achieved this in the past by holding the wood in a clamp, and advancing the drill press downwards very, very slowly, but it's not always successful, because no matter how careful I am, the bit sometimes "grabs" and damages the wood. Can anyone offer suggestions or tips to make this more successful?
 
Did a banister rail with holes at 42 degrees by temporary gluing angle blocks to guide the bit. Once drilled just cut and plane off the blocks.
 
Haha! Thanks so much! I knew someone would have an answer I hadn't thought of! More time-consuming, but an answer that'll obviously do the trick!
 
There's a type of Forstner bit that has a (replaceable) twist drill in the centre instead of the pin you sometimes find, the twist drill is fairly small diameter, about 4mm or 5mm from memory, and you can set the amount it extends to fit the angle you're drilling at. It's designed purely for angle drilling as the twist drill enters the workpiece first and then holds the angle steady and prevents the bit skidding off as the Forstner section starts to engage on one side. I've used them a few times and they do work, I know Famag do them, certainly not cheap but with Famag you know you're buying quality kit.

Good luck.
 
Ouch! I must have been able to buy just the one I needed as I can't see myself spending £222 on five drill bits!
 
I did something similar recently, but in softwood. I did some experiments, and ended up with this approach.

1. I used my drill press, as I couldn't come close to keeping a hand drill still enough.
2. My press has a tilting table, but I kept it square, for several reasons:
- Firstly, these needed to be through holes, and I didn't want to destroy the bit by hiitting the table.
- Secondly, keeping the table square meant it had no tendency to tilt when pressure was applied. Fortner bits do need a bit of down pressure to work.
I built a jig on which to rest the work, and used a guide block to stop the bit wandering at the start.
3. Making the guide block: drill through a large block, square to its surface, then cut it in half at the required angle on the bandsaw (or whatever - I'm lazy!).
- before making the hole, mark and punch the centre for the hole, and take that mark round as lines square to the faces of the block. Then when you are setting out the final hole, you have guide marks to align everything nicely.
4. Making the jig: I needed a set of 1" holes equally and precisely spaced along a piece of roughly 2x1 at an angle of about 30 degrees. This needed two holes in the jig, at the correct spacing, and a removable, snug-fitting peg. The first hole in each piece was made to a mark, then dropped over the second hole aligned by the peg. It's similar to doing box joints on the router table, etc. Each time a hole is finished, that then goes over the peg, so you are lined up for the next one with a consistent gap.

I guess you might adapt the peg idea to work upside down in a movable jig on a large piece of stock. Get the 45 degree guide block right, then split up the offcuts and glue back on either end, so as to make flat surfaces for clamps to hold it to the workpieces (dowel together if necessary). Clamping is difficult, especially if you have a 45 degree angle: on the "upper" side of the hole, the clamp risks fouling the drill on top, on the "lower" side of the hole you haven't got much room to clamp because of the drill table (the table ends up a long way below the workpiece). And on the low side, the clamp can end up under the line of the drill if you're not careful. And they need to be close to the work to avoid movement.

Theoretically a guide on the surface ought to be enough to minimise tearout, but I got a small amount. It might be cleaner if you used a sacrificial piece of something between the jig and the stock, both sides of the stock.

I'm typing this on a tablet at the moment. It really needs a drawing, which I'll try to do if I get a moment.

45 is rather steep for this to be successful, as the edge of the Forstner is trying to tear wood away as it exits the surface (it should be OK once you're completely into the stock though). I'd experiment with sacrificial pieces either side ofthe stock if it's a through hole), and on top if it's blind.

Finally, if you have access to a drill press, use it! In my experience all the power tool wide bits wander terribly, including Forstners, and you're starting the hole very asymmetrically, even with a guide. Rigidity helps.

E.
 
Thanks guys, I seem to have solved the problem. I'd made a jig to hold the wood in place, but it "gave" a little, which enabled the bit to grab. I've re-made the jig, not a pretty thing, but it now incorporates two big clamps, and not one little toggle clamp. There's no movement, and the Forstner bit happily enters at 45 degrees and goes on to drill a nice clean hole right through 30mm of Oak. There's just a little tearing at the bottom, which is easily planed off.

Thanks for your interest.
 
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