Cutting hole through painted f/glass

[Leeroy]

I need to cut a hole for the rollbar as I am looking at mounting a full hoop type
for greater protection for track days.

As my car has been painted for 3 or so years I will need to cut a new hole (60-70mm diameter) thru the passenger guard for the leg but I am concerned
that I might crack paintwork.

Anyone have any good methods to do this without resulting in then


Leeroy

[xlr8or]

Cover it tape first and then drill a pilot hole. After that use a fine tooth hole saw or other blade to cut the hole. Cut it undersized a bit and that will allow you finish the edges by hand and keep the painted edge smooth.

[Rebel1]

What xlr8or said.

[400TT]

Just take it easy with the hole saw, not too much pressure and not too much speed, don't want to overheat the area or start tearing at the fibreglass.

Or do what we've always done, drill lots of small holes around the edge, break the centre out carefully, then file smooth. More chance of causing damage, but works a treat if you don't have access to a hole saw. Or too scummy like us to buy one the right size.

[Tommy]

I like to start the hole saw in reverse so the teeth don't grab the painted surface. After the saw has worn a little way into the surface, stop, put the drill in forward and continue on carefully.

[400TT]

Never tried it in reverse. Sounds like a good idea.

You could always do a test cut in some old fibreglass of a similiar thickness to get the feel of it. Any local fibreglass shop will have a bin full of suitable offcuts. I do this to test with most things, cutting, nutcerts etc.

[CARWARS]

It helps if you lay your tape out in a daisy pattern [with all crossing in the middle] so when you pull the extra tape off you can pull it towards the center so it won't pull the paint from the newely cut edge of the hole.
I have seen a 2 in strip of paint pulled off by pulling away from the hole.
Good Luck!!!

[T E Lewis]

Tommy has the right answer.

We have a boat/marine shop, and we ALWAYS drill the holes (all the way through) w/the holesaw in reverse. No splintering going in, or coming out the back side. Depending on location, we also will use a "roto-zip" w/an abbrasive bit.

[427sharpe]

Tape it, and score the hole carefully with an exacto knife before cutting with a hole saw

[Plums]

Go and buy a "rem-grit" holesaw, I believe they are used for cutting holes in plaster.... They use abrasive grit, not teeth to cut.
I have been using one to cut holes in fibreglass for years now (the same one too).

As suggested here though, go a bit smaller on the saw and hand finish.

[Rwillia4]

It is all about the TAPE!!!

[BMK]

Simple...

Jump in the car head over to Aussie Mike and he will do it for you....

# Make sure you have the drill running at full revs before bringing the holesaw in touch with the tape on the glass.

# Most shattering takes place if the holesaw grabs or is not a full revs prior to contacting the glass.

# Drill the guide hole with a bit the same size as the holesaw guide bit. You may step up to this size with smaller bits.

# Then tape up as suggested, locate the guide hole and go at it slowly.

# Don't push to hard as the final part/section of the cut comes up quickly and if pushing hard you will push the hole saw into the hole bringing the flange in touch with the body around the hole. This will leave a burn effect on the surrounding glass - hence the tape.

Good luck

[jess]

what they said drill in reverse works well even with drill bits

[Leeroy]

Thanks guys for all the very good advise. I will use all these good tips hopefully over the weekend and result in a perfect hole. Next quandry is
making sure my hole is in the right spot.

[David Hodgson]

To avoid splintering on the underside, if you can get the drill and hole saw in there, make a shallow cut from the underside before going right through from the topside.
Like the tree pruners do with a branch.