Drilling fiberglass

[SgBFish]

Hello experts

Just a couple of questions on getting the best finish when drilling through my fibreglass hull.

Should I drill from the outside in or from the inside out? I’m a bit worried if I drill from inside out it may break off extra gelcoat.

For larger holes requiring a spade bit do most people drill a pilot hole first or just go the full diameter they want.

Cheers,
Scott

[FNQCairns]

Without doubt the outside in and if you are really fussy once you see evidence of the drill from the inside you can then drill inside to out very slowly. Consider a layer of masking tape where you drill and take the start slow.

cheers fnq

[Noelm]

a pilot hole on a spade bit is more trouble than it is worth, the bit needs it's own tiny hole to stay on centre.

[SgBFish]

Noel

Are you saying drill a small hole for the spade bit point to sit in to keep it centred?

How fast should a spade bit spin when drilling through glass? Should I go slow then once pas the surface speed it up.

Cheers.

[blaze]

I personally woundnt use a spade bit. My preference would be for a holesaw. That aside, Masking tape on the outside, drill from outside in, grind the drill to a flatter/less cut angle so it has less chance of chipping. I have in the past used a combination of holesaw and spade bit. Drill small pilot hole, say 3/16, use holesaw from outside and go as deep as you can (most often not able to get right through transom (if thats where it is), if possible now do the same from the other side and remove plug. If the 2 cuts havnt completely cut, use a small chisel and remove the ouer layer of glass so you can see the inner core, now use a slightly smaller spade bit and remove core. the hole can then be clean up with a rat tail file.
cheers
blaze

[SgBFish]

Thanks Blaze.

[BR65]

what are you mounting Scott???

[Ringoscar]

Jeez, done a few of these lately! Start on the gelcoat side so you don't rip it to bits when you come through from below.
Use a 1/8" bit or finer to just pierce the gelcoat to locate the bigger bit so it won't skid everywhere. Change to the proper size bit, use a slow speed with the drill initially in REVERSE until through the gelcoat, then switch to forward & raise speed. With the spade bit, just use forward only, slowly until it scrapes its way through the gelcoat without chipping, then go to town. Spade bit from gelcoat side only, it's hard to match track exactly when going both ways.
Same for hole saws but a good one usually cuts gelcoat pretty clean. If going into a foam core layer below, chisel out the foam once it's sawn free from its surrounds, then keep drilling.
Drill dust is real itchy so use barrier cream & then talcum powder up to your elbows or surgical gloves and long sleeves. Vacuum up straight away.

[SgBFish]

Brian
Plumbing my live bait tank at last.
I have to drill thogh 60mm of transom and through the side for overflow.
Scott

[Roughasguts]

I would do it completely differantly again.

I would drill a hole just large enough to stick the sanding drum from my dremmel in the hole, and sand out the hole to the required diameter.

But before that obviously scribe the hole and stick a plastic bag under neath to catch all the dust.

Don't worry it sands out quickly so be gentle with the dremmel.

Ooops just read 60 mm of transom think that's going to be tough going to sand out that depth.

[bar raider]

i agree with the hole saw, either diamond tip (preferred) or saw tooth. (solid ones not cheap split ones).

with saw tooth/bi metal one start in reverse on the gelcoat side caus it grabs real quick and might end up with some chips.

either side first caus when the pilot bit pops through the other side you should then go from that side.

[BR65]

Brian
Plumbing my live bait tank at last.
I have to drill thogh 60mm of transom and through the side for overflow.
Scott
there goes the beer esky

what size holesaw do you need, Ive got the deeper blade ones, should just be a matter of a 3/16 pilot hole all the way thru, bit of masking tape on the gel coat, drill half way from one side, then half way from the other

[SgBFish]

Thanks Brian.

I think I have the gear its getting the nerve up to do it.
Have a great weekend at Mondo.
Keep your eye on the weather and let me know when you are free.
Cheers,
Scott

[honda900]

Hey scott why dont you ask one of the shops to drill the holes for you, wouldnt take much work, just to get that nice proffessional job, Assume it wouldnt cost to much..

Regards
Honda

[levinge]

Go to one of the old seconhand tool places and buy yourself an old hand drill, this way you can go as slowly as you like and won't damage the gelcoat, Masking Tape and outside to in as everyone else has said