Drilling into the gel coat

[chichiflys]

Hello,
Whats the best drill bit to use on gel coat? I am replacing my teak grab rails on the cabin of my H36 and was wondering if there is a preferred drill bit type to use to minimize chipping or cracking for drilling holes. Thanks.

Marc

 

[Maine Sail]

Hello,
Whats the best drill bit to use on gel coat? I am replacing my teak grab rails on the cabin of my H36 and was wondering if there is a preferred drill bit type to use to minimize chipping or cracking for drilling holes. Thanks.

Marc

Bradpoint bits but start in reverse and then switch to forward once through.

You'll want a good set though. Many bradpoint sets are meant for wood only and are soft steel. You want a good high speed steel set. Rockler has a decent set and is what I am currently using.

Don't forget to countersink the hole after drilling to create a good seal for your sealant of choice.

You can see the holes they make in this article:
Potting Deck Penetrations To Prevent Core Rot

 

[SamLust]

You can do the same thing with a standard drill bit. Stroke a small stone against the sharp edge of the tip, holding the stone parallel with the shaft of the bit. This makes the cutting edge broader, causing it to make a "chip" rather than a spiral. Ask any old machinist about this old trick. The real issue here is countersinking. In addition to providing a well for sealant it provides relief for the gel coat around the hole. If yo have a perfect clean hole and run a self threading screw into it you WILL get gel coat cracking. If you cut the gel away by about a third more than the diameter of the screw it won't happen.