How do you screw into fiberglass/gelcoat without chipping?

[guy48065]

Yesterday I added attachments for a bimini top on my bowrider. All the holes I drilled chipped a bit when driving the screw in--one of them badly, so it shows.

For the NEXT time--what's the trick in preventing chips/flakes?

 

[airshot]

That is worse for than just chipping, ouch !! I use special drill bits that cut the OD of the hole, these are called sheet metal drill bits. Also add some tape before drilling, then drill thru the tape...it does help. Std drill bits are not made to drill thin sheetmetal or fiberglass.. I know, this is easy for me to say....as a retired toolmaker, I grind my own drills for the job at hand.
Hope you have a backing plate or other support on the back side of those screws or they will pull out and leave a bigger hole...good luck

 

[MikeSchinlaub]

Predrill the hole, then use a counter sink bit. What happens is the screw pulls on the gel coat, as well as pulling itself into the hole, and it cracks. The counter sink bits will cut the gel down so the screw doesn't grab it.

Also, for any hardware like dash panels and speaker covers, use a screw smaller than the mounting hole on the hardware. That's why lots of dash panels and plastic glove boxes are chipped and cracked around the holes. The screw either pulled the piece or was too big and pushed the hole open until it cracked.

 

[alldodge]

Easiest way I found is run the drill in reverse until you make it thru the gelcoat. You can continue clear thru in reverse so long as you don't run into wood or other, but can go forward once past gelcoat. I like drilling thru gelcoat with a slightly larger whole than needed, switch to correct size once thru gel

Drilled maybe 40 holes for my new canvas cover, not one chip

 

[Fun Times]

Masking tape down and running the drill in reverse first tends to help a lot.

 

[Mc Tool]

Are they self tapping screws ?
Plus me for the countersinking

 

[Scott Danforth]

Drill thru the gel with bit in reverse. The switch directions. Counter sink the hole

 

[cyclops222]

I use a micrometer to get the right sized drill for the final pilot hole

 

[redneck joe]

Predrill the hole, then use a counter sink bit. What happens is the screw pulls on the gel coat, as well as pulling itself into the hole, and it cracks. The counter sink bits will cut the gel down so the screw doesn't grab it.

Also, for any hardware like dash panels and speaker covers, use a screw smaller than the mountingView attachment 411428 hole on the hardware. That's why lots of dash panels and plastic glove boxes are chipped and cracked around the holes. The screw either pulled the piece or was too big and pushed the hole open until it cracked.

This is best

 

[redneck joe]

Easiest way I found is run the drill in reverse until you make it thru the gelcoat. You can continue clear thru in reverse so long as you don't run into wood or other, but can go forward once past gelcoat. I like drilling thru gelcoat with a slightly larger whole than needed, switch to correct size once thru gel

Drilled maybe 40 holes for my new canvas cover, not one chip

This is second best. Both effective i just prefer to have more drill bits.

 

[alldodge]

This is second best. Both effective i just prefer to have more drill bits.

Everyone has an opinion

 

[MikeSchinlaub]

Everyone mentioning the method of running the drill in reverse makes me think of a way you SHOULDN'T do it.

Don't predrill, then try to countersink with a bigger bit. It will do the same as an oversized screw and grab the gel, lifting and cracking it.

 

[JimS123]

Drill a hole that is appropriate for the screw being installed. Then drill thru the gelcoat with a second bit that is slightly bigger than the screw's OD. Works every time.

I learned that in 1971 when I bought my first glass boat. Haven't chipped a screw hole since then.

Regardless, if you have access, use bolts instead of screws.

 

[cyclops222]

Think of a Fibreglass surface. Then put onto it a coating that dries as hard as glass. I pilot the hole to be as wide as the widest part of the screw shank. Maybe .010 " larger. Then only the screw is pulling UP on the unseen inside surface.

 

[redneck joe]

Everyone has an opinion

Yessir, we all have one.

 

[guy48065]

Actually I did begin countersinking before I got to that hole. Not wide enough...not deep enough? I could see it went thru the gelcoat but maybe it just weakened it. The pilot holes I drilled for these 2 loops were close to an edge. I'm thinking the gel was thicker here than on the flats where the other attachments are, the chipping was very minimal there.

 

[MikeSchinlaub]

I zoomed in on your picture. It looks like you didn't get deep enough. You should be down to the glass around the edge of the hole. You may need to use a smaller counter sink bit, so you can go deeper without getting past what the hardware will cover.

Run the screws in slowly by hand, and keep a close eye on how the threads are catching on the gel. If there is even a slight flexing, back out and counter sink just a bit more.

 

[guy48065]

I appreciate that.
If there's ever a next time I'll drill stepped pilot holes.

 

[Mc Tool]

After seeing the above I think I would try a dremel with either a bur or a stone to wizz thru the gelcoat.

 

[mike_i]

Yup, this is the way to do it.

Masking tape down and running the drill in reverse first tends to help a lot.