Drilling holes & self tapping screws

[david_e]

Is there a combination of sizes for drills and s/t screws that is best used when fixing items onto areas of the boat that have a gelcoat finish. I recently needed to fix something relatively small, the hole was fine but when putting the screw in an area of gelcoat around the hole came off with the pressure from the screw. I note that where the builder has done this there is no problem. Help please.

 

[burgundyben]

I nmy limited experience of drilling holes in GRP, I drill the hole, the do a little countersink just by twiddling a bigger drill bit in the hole with my fingers, remove just a little bit of the gel this way stops it from cracking

hope this helps



......girls, girls, get back, please, one at a time......

 

[JohnR]

Basically what BB said. In GRP you need to drill a bigger pilot hole than you would for wood i.e. so really just the threads have to catch, then use a sharp countersunk which will stop that nasty shard flying off.

 

[bryantee]

have a look at http://www.metric.fsworld.co.uk/sidrill.htm and classic marine do a list of sizes for wood screws on their information page.
good luck.also check hadfield marine,i think they have a list of drill sizes for self tappers in grp
Srew fix have a table for wood screws on page 10 of their catalogue

<P ID="edit"><FONT SIZE=-1>Edited by bryantee on Sat Jun 22 04:55:14 2002 (server time).</FONT></P>