How to make a hole larger?

On another boating forum a friend of mine posted a tip I'd never thought about so I figured I'd repeat it here, albeit without the photos he posted.

So let's say you have a 2" hole through your gelcoat or whatever material, and you need to enlarge it to 3".

First step is to tape off the entire around the existing hole, covering an area at least an inch or two around the larger hole you want to make.

Next, on your drill mandrel, mount the 3" hole saw. Then, using the same mandrel, mount a 2" hole saw inside the first one.

Carefully center the 2" hole saw in the existing hole and very gently lower the bit into the hole. Keep it centered so it doesn't run away across the gelcoat.

When the 3" hole saw comes in contact with the tape hold the drill steady and VERY gently lower it until the 3" hole saw bit comes in contact with the gelcoat. Let the teeth on the 3" bit start to eat their way through the gelcoat. The 2" bit will keep the bit centered as the 3" bit works its way through the material you're cutting through.

After you've finished drilling the 3" hole stop the drill and pull it back out through the hole. Remove the 2" hole saw from the bit, then remove the collar of the material you've removed.

Bingo you just finished enlarging your hole.

Great tip!

Thanks for posting. Never thought of this.

Bennett

Good tip. Use the 2 inch as a bushing or guide.

Brilliant

another way is to drill a 3" hole in a piece of wood and glue it over the 2" hole with hot glue then drill the hole out with the 3" and when done smack the edge of the board with a hammer and it will come off ( as hot glue is not a permanent glue or heat the wood with heat gun then tap) and if any glue remains its easy to get off , sometimes you can clamp the board in certain instances.

Great tip!

Cool idea.

MM

Why didn’t I think of that... Simple and brilliant

Great trick, but beware, not all mandrels will allow stacking.

Wylie_Tunes said:

Great trick, but beware, not all mandrels will allow stacking.

Click to expand...

Correct - mine don't.

I usually start the hole saw in reverse or counter clockwise. The teeth will still bite into the gel coat but less likely to tear out chips. Once the cut has started, set the drill to "normal" clockwise rotation.