# How Do I Successfully Drill Thru Fiberglass?



## Baysailor34 (Dec 8, 2003)

I need to drill a few holes thru my lazarette sides to attach a piece of hardware. The last time I drilled holes in this area was when I installed some hasps to be able to lock the lazarette down. When I drilled the holes that time there was some chipping of the fiberglass around the hole entries. How can I prevent this from happening the next time?

Thanks.


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## scottyt (Jul 19, 2008)

the most sure fire wire way to stop the chipping is to use a spade bit to start thru the gelcoat, the ones with the tips on the out side. then use a normal bit to finish, the problem lies with the spade bits dont last long. ( speed bore IIRC ) 

the other option is to try it in reverse until you are thru the gelcoat.

some people also drill it out in several steps, start small and drill out bigger, and bigger until it is the size you need.

or go buy some brad point bits, and use those but they wont last long either


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## PaulinVictoria (Aug 23, 2009)

I used a brad-point recently to mount my new Tacktick head unit, went through perfectly. Don't press on the bit, allow the bit to cut with as little pressure as possible. You might also want to use a bit of tape, I didn't bother as the brad point tends to prevent slippy-slidey anyway.


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## L02314564 (Jul 3, 2007)

I agree with Scottyt about drilling it out in several steps, start small and drill out bigger, and bigger until it is the size you need. But I don't agree with the spade bits. Unless the spade bit is kept sharpened it will destroy the gelcoat much like the drill bit did to you before. 

PaulinVictoria have it right as well with the brad-point. The tip regarding the application of very little pressure to the bit should be applied to all bits when being applied to fiberglass. 

All the best.


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## mdbee (May 2, 2007)

Another way.. 3 different drill sizes but a different order.

First use a smaller drill bit to make a hole.
Then use a bigger than needed drill bit to just drill through the gelcoat, (not the fiberglass) this will allow you to use the final drill bit, to drill through without causing the gelcoat to crack. 

Practice first.


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## DelmarRey (Aug 25, 2001)

One more trick is to press hard or use thin two sided tape, on a sacrificial 1/4" sheet plastic or fiberglass against the surface. Then drill thru them both. It keeps the drill from grabbing the gelcoat and chipping it away. With tape you'll want to *twist it off* not pull off the plate. For alignment a small hole in the sacrificial plate is used to line up a mark (X).


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## HDChopper (Oct 17, 2010)

Or you resharpen the bits used for fiberglass just as one would for plxie glass / steel / plastic / all mediums require different angles for the cutting face of any machine tool ..

Your answer is eazy to find on the web looking under machining.

Good luck.


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## RichH (Jul 10, 2000)

The BEST way to drill into fiberglass (gelcoat) to prevent chips and tearouts of the gelcoat ... use a portable drill press (or first drill a very small pilot hole if you dont have a press), set up the alignment of the bore, put down a section of masking tape onto the gelcoat, and before your drill put down a sheet of fine (100 grit) sandpaper (face side down) on top of that, and SLOWLY increase pressure of the drill tip as you begin to penetrate through the inverted sand paper and masking tape. Will be 'perfect' hole and without 'tearouts' and flakes .... because the drilling begins as a 'grinding' due to the sandpaper grit ... the masking tape 'strengthens' the gel. Slowly PEEL the masking tape away (alsmost folding the tape over onto itself) when done, dont 'rip it off' nor pull 'up'.


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## Maine Sail (Jan 6, 2003)

Bradpoint bits but start in reverse and then switch to forward once through. I've drilled literally thousands of holes this way with zero chipping..

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 if bedding the hasps.

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

HSS Brad Point:









Clean Holes:









Done right and started in reverse a good set will even make near perfect holes in PAPER!


















Starting in reverse is also a key trick with hole saws too. You can drill clean holes even though headliner fabric & vinyl by beginning in reverse. Once through the gelcoat, which is easy, flip it to forward..


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## HDChopper (Oct 17, 2010)

Yes MainSail , a Fostner type looks like the type to use for FG ...


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## sailingdog (Mar 19, 2006)

*Don't forget to run the countersink bit in reverse as well. *Gives you far more control over the depth of the countersinking and eliminates the risk of chipping almost completely.


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## boofus (Jul 27, 2008)

Depends on your countersink, a typical hardware store multi-flute will chatter like hell if not done just right. I agree that reverse in a "soft" material is the way to go for the most control. Using a single flute or zero flute bit typically produces much better results. Either of these types wont do much in reverse.


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## Cruxandreams (Mar 8, 2011)

Drill in reverse has always worked for me with no chips


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## Redfin (Feb 20, 2011)

I agree with MainSail. BTW HDChpper. I think you meant `brad point' bit and not a `forstner' bit. I have sometimes made up my own brad pint bits by grinding down a regular twist drill. It works. For larger holes then you have to move up to a hole (core) drill.


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## omaho5 (Jun 5, 2008)

Hell, I'm no expert. That said as a retired contractor, I would use green automotive tape. Apply thiis to the substrate to be drillled. Mark on your taped area the point of drilling with a grease pencil.
next, use a "Forstner bit" on SLOW speed to drill hole through the substrate.
Start with a Forstner bit pilot whole to see how ts iis going to look before going to the diamter of desired hole.


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## GaryHLucas (Mar 24, 2008)

I hate to disagree with a few people, but starting with a small hole and stepping up in size is just about the worst thing you can do. Once the point of the drill is no longer pushing against the material the flutes just grab and rip a big mess. What you need to do is remove the hook from a conventional twist drill. I have attached some photos to show how this is done, using a diamond hone or stone. You need to do both flutes.

We use this to drill holes clean holes in fiberglass, polyethylene, copper and lead. I have drilled 1/2" holes through 2" of copper using a drill sharpened like this. The hole was smooth and clean, like it had been reamed.

I hope this helps,

Gary H. Lucas


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## fallard (Nov 30, 2009)

The use of a brad point bit, as recommended above, is appropriate for smaller holes, whereas the Forstner bit is a larger diameter equivalent to a brad point bit. The photo shown in the Maine Sail post shows a cored deck or bulkhead, where the use of a portable drill press can be very important, particularly if you need to line up a backing plate. 

It is also helpful if you start with a smaller pilot drill and then use the brad point or Forstner bit from both sides (assuming the back side is accessible) to prevent the back side from tearing out. 

If your project is exposed to weather, I'd wet any coring that is exposed with epoxy and then use a proper bedding compound.


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## hellosailor (Apr 11, 2006)

The points, the angles, sharpening, starting in reverse, but I'd also suggest using a center punch or awl point to mark a center, so the bit doesn't wander, and starting slowly, so it gets to grab and center without skittering around any.

When all else fails, you put a trim washer over the hole, to hide the chips.


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## Maine Sail (Jan 6, 2003)

hellosailor said:


> I'd also suggest using a center punch or awl point to mark a center, so the bit doesn't wander, and starting slowly, so it gets to grab and center without skittering around any.


With a brad point in fiberglass this is not necessary. Today while installing a battery monitor on a customers boat I remembered to take some pics for you guys. Drilled this hole today. Measuring for it took far longer than the act of drilling..

The only reason for tape was to mark my hole center and I get holes just as clean without tape:









I then drilled a 1/4" pilot hole, the same size as my hole saws arbor drill, using a brad point drill bit:









Started in reverse with the brad point and once through the gelcoat I switch to forward:









Then I busted out one of my trusty Lennox hole saws and drilled through about half way in reverse before switching to forward:









Hole done, no chips and perfectly clean:









Just for you guys I saved the plug to show how easy this is:









The right tools and the right technique make for easy work..


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