Thread: Enlarging existing hole - any tips?

Hot melt glue or if you a careful and don't go outside 60mm 5 minute epoxy some scrap ply (a strip is all is needed) on the side you are drilling, need to centre a pilot hole. This should give you enough support till the saw bites enough to stay in the one spot.

Just a thought.

Cheers

Originally Posted by Karsten

Hi, trying to enlarge an existing 52mm hole through 12mm fibreglass to a dia of 60mm.Karsten

Just plug the hole with a suitably sized wooden plug then re-drill new hole with larger hole saw

Sprog has it. Using a 52 mm hole saw, drill out a hole blank from a similar thickness of material. Change the hole saw to 60 mm and slip the 52 mm piece over the pilot bit. This may tend to pich and bind, so if it was me, I'd just glue the 52 mm blank into the current hole. When dry, use the pilot hole from the freshly glued in blank for the 60 mm hole saw.

A method I use is to drill your bigger size hole in some scrap that is big enough to be centred over old hole while being clamped in place. Scrap can be any size so that clamps can reach it.

Thanks all for your replies - all make good sense.
Situation makes clamping a bit difficult, so I'm going with gluing a rough plug into the existing hole, probably using 5-min epoxy (plug and glue residue will be cut out when the 60mm hole saw goes through).
Although I do like PAR's option of fitting a 52mm round disc on the holesaw drill bit, to keep you centred in the existing hole - very neat! But as he says it will probably bind - in some situations you may be able to use Alu tape or another covering to smooth the outside rim of the disc to reduce binding. I'll keep that one in the drawer for now.
Again, all inputs appreciated.
Kasten

The 52 mm disk on the pilot bit trick I mentioned, I've done and it only has to keep you centered long enough, to put a few mm's of cut on the bigger hole saw. Once the 60 mm saw gets started, you can remove the 52 mm piece and continue with few worries, as the hole saw will settle in the new "kerf". It depends on how good you are at handling your drill and hole saw. If you can get setup in a good position over the work, with a good grip, then the 52 mm disk trick will work. If on the other hand you have a lousy angle and can't get over the work, you'll want a more secure method, such as gluing in a hunk of material.