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  #11  
Old 03-01-2011
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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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Old 03-01-2011
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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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Old 03-18-2011
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Drill in reverse has always worked for me with no chips
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Old 03-19-2011
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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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Old 03-19-2011
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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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Old 03-19-2011
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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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How Do I Successfully Drill Thru Fiberglass?-1.jpg   How Do I Successfully Drill Thru Fiberglass?-2.jpg   How Do I Successfully Drill Thru Fiberglass?-3.jpg   How Do I Successfully Drill Thru Fiberglass?-4.jpg  
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Old 03-19-2011
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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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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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Old 03-25-2011
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Quote:
Originally Posted by hellosailor View Post
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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Last edited by Maine Sail; 03-30-2012 at 11:38 PM.
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