Hole in Wood too Small

[Nitell]

Hello guys,

I used a Core Drill to cut a 12mm hole in wood about 90mm thick.

The hole is too small, but I don't think it is wise to try and enlarge it with another Core Drill.

Can anyone advise if a 20mm stepped Cone Drill will cut wood 90mm thick?.

Thank you for any advice.

 

[Munroast]

what size hole do you want ?
if you are going from 12 to 20 then you would get away with it using a pillar drill and firmly clamping the work piece down.

the other way would be to insert some form of wooden plug into the 12mm hole and start again. Wood is quiet giving so any roundish 12mm plug should hammer in reasonably well.

 

[Diver Fred]

Hopefully the piece that the hole has to be drilled into has enough surplus material around it to either clamp or screw a scrap piece to.
With a Forstner bit of the size you wish the extended hole to be drill through the piece of scrap, the piece of scrap needs to be the same thickness or thicker that the depth of the Forstner bit. Once that is done firmly fix the piece of scrap over the existing hole where you need the extended hole to be. Once that is done, using the same Forstner bit and a slow drill speed redrill the hole using the hole drilled in the scrap as a guide. Once the bit is fully in the hole you can remove the piece of scrap and then continue to drill the hole as the sides of the extended hole will act as a guide for the Forstner bit.

 

[^woody^]

Clamp or fix another piece of wood of the face and this will guide the core bit. This won't need to be very thick.

 

[rsgaz]

a 20mm stepped Cone Drill will cut

That will take forever, require some serious downward pressure, get extraordinarily hot and scorch your workpiece.

If the hole doesn't need to be perfectly neat, I'd just drill it out with a 14mm HSS bit, then a 16, 18 and then 20. Depends if you have HSS bits in these "blacksmith" sizes. Normal sets only go up to 13mm of course.

 

[Nitell]

Many thanks for your replies.

Apologies. I should have mentioned that the (wood) area I am drilling is a section above a UPVC window, so cannot be clamped.

I have many drill bits, maximum about 10mm. As suggested, might be best, and cheaper, to plug it and drill with 20mm wood bit.

Thanks to everyone.