The grand kids are coming for a holiday. I have a composition material medicine cupboard with no lock. What is the best bit to use the make a clean, 20mm cylindrical hole in the door?
I have a Forstner bit which I've used for some stopped housing jobs but to go all the way through, wouldn't I need to drill a pilot hole which has tended to cause loss of Forstner bit centering in the past. Is there a more suitable bit?
The Forstner bit has its own centering tab so no pilot hole is needed.
You will need to securely clamp a piece of scrap wood to side of the door that the bit exits so that you don't get breakout and to give something for the Forstner bit centering tab to bite into for the last
5/10mm of the cut.Consider the clamped bit of scrap wood as just making the door thicker so effectively you are not drilling through the complete thickness of this combined material.
The above assumes that what you are drilling through is not hollow beneath the door skin.
Probably put some masking tape on the front surface of the door which may/will prevent cosmetic damage when drilling.
If you can use a stand drill you stand a better chance of keeping the hole 90 degrees to the door front.
An alternative to clamping a back piece is to drill slowly and carefully. As soon as the tip of the forstner appears stop drilling and start drilling fom the othe side
An Auger would produce a clean hole with a scrap piece clamped to the back. The beauty of Augers is that having a lead screw as the drill breaks through the lead screw tends to pull the scrap piece tight onto the back of the piece being drilled.
Richard
If you haven't got a drill press I think you will struggle to use a Forstner bit in a hand-held drill (I haven't tried it) without making a guide.
As an alternative you could use something like this:
Thanks all for the good advice. I'm going to go for the auger bit option. The forstner bit might make a cleaner cut but for exit purposes I'll feel more comfortable with the auger bit.
Naah....
But: so make a guide. Bit of wood, drill through at the angle you would like (here: 90°). Don't do this on the workpiece, just make the hole.
Apply wood-with-hole to front of workpiece, adding a bit of undrilled wood to the back of the workpiece. Clamp the lot.
Drill. Wood-with-hole guides & hold perpendiclular, wood in back prevents tearing on exit.
Can't slip, can't scratch the surface, hard to get wrong...
Thomas Prufer
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