Using a fostner bit on an angled workpice

E-wan · 15 Oct 2018

I want to cut a large hole approximately 50 mm in diameter to slide a pipe through a pice of wood at 45 degrees.

Assuming everything is held in place very family buy bolting the workpiece through slots in the drill press table are there any safety concerns for trying to cut this with a fostner bit in a drill press?

Diagram below

Thanks

Ewan

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Phil Pascoe · 15 Oct 2018

If you want a clean, accurate hole I would hot melt glue a wedge on top to make the entry level. A 2" bit should be strong enough to start without to much deviation, though, and a decent one should do it without ripping.

Droogs · 15 Oct 2018

Personally I would make a guide that mates with the above and can be clamped firmly in place as well. That allows the bit to enter perpendicular to the horizontal and then peck drill until I knew the forstner bit was well into the lower piece. Remove the guide and than continue until done. This ensures that the bit enters exactly where wanted and as true as possible.
HTH

Seiken · 15 Oct 2018

If you have not already cut the workpiece to shape drill first while the blank is square then cut to shape.

Eric The Viking · 15 Oct 2018

I'm with both Droogs and Phil P.

I had a project that needed six holes like that, so made a jig to support the workpiece at the correct angle, and a guide, made by drilling through a block then cutting it on the correct angle, which could be clamped on top.

I find alignment is tricky when doing this sort of thing. It helps a lot to make your guide block dead square before drilling - it doesn't have to be a cube. If you mark the centre with lines that go to the block edges, and carry those down the sides too (and then cut through it at an angle), you can use those for dead-on alignment later, by making similar lines on the workpiece.

As long as the Forstner bit is tightly constrained by the block, and that in turn is tightly clamped to the workpiece, you shouldn't get tearout on the upper side. You can avoid it completely on the other side by clamping a piece of waste to that, but for a lot of big holes you will need a lot of "waste" available.

Also helps if your Forstner is properly sharp to start with. And for 50mm diameter I'd have the pillar drill on a slow RPM as the linear speed at the edge will be quite high otherwise.