Advice on best way to put screws into gelcoat?

[Darren Mc]

Can anybody tell me the best way to put screws into gelcoat without making a big mess of the gelcoat. I'm thinking the pilot holes i'm drilling aren't quite big enough and that's what is causing the gelcoat to crack and chip away when I put the screw in? Is this right or am I off track?

[WalrusLike]

I haven't experience but believe the secret is to countersink the hole.


(Using Tapatalk on iPhone so can't easily 'thank' or 'like')

[thylacene]

Use a drill that is the correct size for the screw, that is marginally larger than the shaft of the screw, hold the shank of the drill behind the screw, you should be able to see a small amount of the shank either side. Then use a countersink bit and countersink the hole by at least two millimetres. Stick the screw into the nozzle of the Sikaflex so at least half the length of the thread is covered. For screws 8 gauge and larger it is better to use a "rattle gun" driver.

Reasoning:

If the hole is not marginally larger than the central diameter of the screw it will jam and strip.

The countersunk hole avoids chipping as the edge of the gelcoat is not picked up by the thread.

The Sikaflex doubles as a lubricant, reducing the likelihood of stripping the head, provides sealant and minimise the chance of coming loose as it is adhesive when dry.

Recently had to drill 24 x 3/16 x 1" screws into a transom under the water line to fit trim tabs, not one chip, no leaks, no stripped screws.

Almost forgot the most important thing, use good quality hardened bits that are the right size for the screw. Once started, drive the screw right home, you can remove it again if you are fitting up, but is best if you run it in completely, minimizes the chance of it biting and stripping the head when fitting the second time.

All of the above learnt the hard way of course.

Hope this helps.

Thy

[gofishin]

Good advice above. If you don't have a csk bit, just use an oversize drill bit (than you need for the screw) and use it in reverse. PS. It needs to be sharp, and not bigger than the screw head. Then change to the correct bit and drill away.

I actually use this method all the time, works 100% too.
Cheers
Brendon

[Blackened]

G'day

Another tip, use some masking tape (the 3 day stuff, not the horrible, you'll never get it off stuff) over the intended hole, this will help prevent the gelcoat cracking, and use the drill in reverse for the initial contact.

Dave

[Darren Mc]

Thanks for all the info, i'll follow those tips from now on. I think I may have been using to small a pilot hole for size screw by the sound of it. Cheers for all the help guy's.