Drilling GRP

[vyv_cox]

Reinvigorating an old thread, but it's taken a few weeks to get to some GRP to drill a hole to take some photos.

When I was having a new boat built I went to the yard during fit-out for a viewing, and guess what drill bits the fitters were using? Good enough for them...

I suggest a brad point bit for holes up to 12mm. For bigger holes use a hole saw. The reason why these drill bits cut gelcoat cleanly is because they have sharp teeth on the circumference, just like a hole saw. These score a clean groove in the gelcoat at the edge. Once this groove is cut you can drill away without risk of chipping the gelcoat.

Here's a sequence of how to do it...

1) Position your hole using the sharp point
View attachment 208037

2) Push in until the outer teeth are just scoring the surface and go slowly and gently here until you have broken the surface of the gelcoat all the way round
View attachment 208038

3) Now drill the hole normally. You get a clean chip free edge
View attachment 208039

This is a brad point bit. They don't last long in GRP as they are only hardened for wood, so after half a dozen holes they are done. However, they only cost a couple of pounds each.
View attachment 208040

At 12mm you could use a hole saw or a brad point bit. Above 12mm definitely hole saw. Below 12mm? I use these. Completely inappropriate tool for the job? Oh I expect so. Does the job perfectly? Seems to.

I have a set that I use for wood and, occasionally, aluminium. My set appears to be hardened steel but many are not. Life in GRP would be far too short for me. I have owned my 12 mm hole saw for many years, during which it has drilled countless holes in steel, aluminium and grp.