I want to install some 3 3/4" stainless cup holders in my dash. Whats the best way to cut through the gel coat without chipping? Are there any good Dremel attachments?

WORD of advise -
Just make DAMN sure that it will fit BEFORE you cut the hole.
I measured twice and cut once and the new radio location still almost didn't fit. It JUST fit.

A bimetal hole saw will work fine.
Here's the routine:

1) drill a thru hole the same size as the pilot on the hole saw.
2) run the hole saw BACKWARDS to get it started thru the gel without chipping. Once you have cut most of the way thru the gel, before you start cutting glass, change rotation to the normal direction and proceed with normal speed and light pressure.

If you need the far side to remain clean, cut only 2/3 of the way thru, then finish fro the reverse side. If the farside doesn't matter, then go thru from the front - as you get ready to break thru rock the hole sawl fro side to side as it spins.

After you cut, you can lightly clean the gelcoat with a 45 degree chamfer with a sandpaper roll on the Dremel. Usually don't need to, though.

What he said...

...and I'd also cover the area with masking tape as an extra precaution.

D. Ocean
Pompano Beach, FLA

The absolute best thing to use on fiberglass is a carbide tipped holesaw. You can pick one up at any plumbing supply house. Lenox makes one in 3 3/4 or 4". The 4" sells for around $55 or so. With carbide you will not get ANY chipping as it enters the fiberglass.

Also keep a shop vac running next to the hole as you're drilling

I've had great success using a dremel tool with a roto zip bit. I cut out all of my speaker holes, half a dozen gauge holes, and some pop up cleat holes. I usually put the Blue 3M masking tape down as a precaution and you can still see your pencil line through it.

Mark

Thanks for the ideas. It would actually be easier for me to cut the hole from underneath the dash. Otherwise, I have to remove the windshield. Because of this, maybe the dremel would work best.

If you use the dremel put it in a plastic bag and extend the bit thru the bag I do this with rotozips cuts dust down from flying all over the place

If you can only go from underneith then I would still use the hole saw, but I would use the same method that Mcolist said however I would score the Gell with a razor blade just to the outside of the hole. Then I would not push hard at all and just let the bit do its thing.

Jon