Making holes

[Wizzle]

Morning all.

My rolling chassis is imminent from Al, so I thought I’d get the rear lights in place and crack on with a bit of wiring

Thing is, I’ve never worked with fibreglass before, and I don’t want to make a mess… I need to make 34mm holes for the lamps, as well as the smaller holes for fixing bolts, and I’ve read a range of different approaches on car and boat builder sites. Some say you need a diamond hole cutter, some say a hole saw running backwards, some say approach from each side and meet in the middle…

Does anybody have a tried and tested approach? Currently a pilot hole followed by a reversed hole-saw seems to make sense from what I’ve read, but I’d appreciate any tips!

Thanks

Alex

[Weg]

An easy way without spending loads of money on diamond tipped cutters.
Grind a negative cutting angle on normal twist drills, they will then be scraping the gel coat and not cutting into it making a mess.
Keep those selected drills for that purpose, they won't cut anything else.
For the bigger holes, stitch drill all round just inside of your cut line then finish off the rough hole with a file or coarse rubbing down paper on a big stick.

[Richard and Pat]

It is a good idea to put masking tape over the area you want to work on and always start with a small pilot hole. I have found the muti-drill specials very useful.
If you cover oversize the area you want to drill then use a compass and create the outside diameter required followed by a second circle inside leaving the gap the size of the drill in use for the chain drilling [e.g. 3mm] once complete use an Abrafile or coarse round/ rat tail file to join all the holes and finish as Tony says.

[Wizzle]

Useful tips, thank you both!

[Throwley]

I apply masking tape to the whole area - a bigger area than you'd think - in order to guard against bumping the gelcoat with tools. Then put your safety specs on (you don't want gelcoat chips in your eye, trust me) chain drill with modified bits as per Tony and use an Abrafile or a burr in the Demel (but careful 'cos these heat up v. quickly) to join the chain and remove the bulk of the material. A round hole can then be tidied up and brought to size using coarse emery or glasspaper wrapped around a length of dowel or plumbing pipe, but careful, because material comes off quickly and you can easily go oversize. Check often! I also tend to run a smear of epoxy along the finished raw face to prevent wicking and/or delamination.
I've also had good results on GRP using a skin knife - a hooked tool made from an old hacksaw blade common in aircraft skinwork - to scrape the material away until you're through. This, however, takes AGES, so I've only ever used this for odd profiles or shapes where the Abrafile won't reach.

[Wizzle]

That's great, thank you Throwley!