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Old 04-25-2004, 11:18 AM
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Default Drilling Holes In Fiberglass

What are the best drill bits and correct way to drill ... .....GULP!! .....holes in new fiberglass??
I've seen it done where they apply duct tape to the surface to prevent cracks from what I can tell..

Thanks
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Old 04-25-2004, 11:33 AM
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Default RE: Drilling Holes In Fiberglass

Up to 12" holes we use regular sharp drill bits. Anything over ,go with the a hole saw in lieu of bigger drill bits. The bigger drill bits really chew when penetrating and really blow out the glass*when exiting.



FYI...Remember to countersink the gelcoat when using self tapping screws. We have found if you dont, you may have problems down the road with stress cracks coming from the screw area's.



SIM
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Old 04-25-2004, 11:42 AM
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Default RE: Drilling Holes In Fiberglass

I'll add one more to SIM's list.** In drilling thru the top decorative gel coat sometimes you can get chipping.* To avoind this consider running the drill in reverse and basically rub thru the gel to the glass. then turn forward.* Use very little pressure and hold back to try to prevent that grab and pull thru SIM describes.
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Old 04-25-2004, 11:43 AM
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Default RE: Drilling Holes In Fiberglass

Does applying duct tape over the area to be drilled help in any way?
I've seen plumbers drilling holes in fiberglass tubs do this.
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Old 04-25-2004, 12:04 PM
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Default RE: Drilling Holes In Fiberglass

Thanks for asking the question as I've been curious myself.

Also, how do you countersink...is that just using the bit to grind a cone or bevel so the screwhead sits "in" it?
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Old 04-25-2004, 12:41 PM
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Default RE: Drilling Holes In Fiberglass

3/32" drill bit for #4 screw. 1/8" drill bit for #6 screw. 9/64" drill bit for #8 screw.

11/64" drill bit for #10 screw. 3/16" drill bit for #12 screw.


Also, here's a trick I picked up from a magazine article that really makes a difference. Before installing a wood type screw into fiberglass, cut a groove on both sides of the tapered portion of the screw. Essentially making it a self tapping screw. This cuts down significantly on chipping/cracking when installing the screws. I use a metal cutting disc on my dremel tool to enhance the screws in that way. But according to the article, filing or grinding the screw flat in those areas will work almost as well.
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Old 04-25-2004, 01:15 PM
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Default RE: Drilling Holes In Fiberglass

Husky,

I dont know if you can get countersink bits a Home Depot ect but we have several different sizes for countersinking aluminum or steel plate for a flat or oval head fastener. The smaller*CS bits*for say up to 1/2" dia are about $7-8 a piece.

*If I am in a pinch and dont have one I will use a larger drill bit in reverse and this will have the same effect as CS bit but the countersink is not as pretty looking. God forbid if you forget which direction the drill is on either with a bigger drill bit .



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Old 04-26-2004, 06:41 AM
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Default RE: Drilling Holes In Fiberglass

Here is what I do:

1) Utilize a bit that is only slightly undersized versus a typical wood screw pilot hole. It doesn't take much stress to crack the glass/gelcoat. Using tape over the hole location will keep cracked chunks in place for re-attaching (if this occurs).
2) Countersink the hole using a dedicated "star" type countersink to prevent subsequent cracks.
3) Lubricate screws with caulk, WD40, wax, or something depending on whether a seal is required. Bed the hole with 5200 if below the waterline.
4) Don't let the drill bottom out hard or you risk cracking; snug the screw tight gently. Sometimes I run the screws in a little at a time, then remove them to blow the dust out before continuing.
5) When drilling large diameter holes I use forstner bits. They are expensive but I have a full set for woodworking and they are the bomb. Drill slowly to resist building up heat. When the pilot point reaches the exit surface, drill from the other side to complete the hole -- no blowout this way. With a hole saw you can do the same thing.
6) When cutting fiberglass with a sabre/jig saw, use laminate cutting blades. They cut only on the down stroke, which is the reverse of typical blades. This causes much less surface damage. Mask off the area to cut with tape -- this prevents marring the surface with the shoe of the saw.
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Old 04-26-2004, 08:59 AM
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Default RE: Drilling Holes In Fiberglass

To prevent chipping use a "crown point" bit. It looks like it sounds, it has 3 points. The center points keeps it centered while the outer point cuts cleanly thru the gelcoat. They don't last as long as regular bits, but we use them in a production enviroment and feel its worth it.

Also for larger holes, a "forestner bit" drills a sharp clean*hole. Again not the longest lasting bit but for the occasional hole in you boat both types will last most boaters a lifestime.

Both bits are availabe at Lowes or Homedepot. You can pick up a countersink while there. I prefer the ones for steel as they cut cleanly.
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Old 04-26-2004, 09:39 AM
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Default RE: Drilling Holes In Fiberglass

Thanks. Gotdang! this is a great board.
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Old 04-26-2004, 11:55 AM
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Default RE: Drilling Holes In Fiberglass

Use a Uni-Bit. You'll get perfect, chip-free holes everytime. Do a search for "drill" or "drilling" and you'll find numerous discussion about this in the past.
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