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Author Topic:   best method to drill large hole in gelcoat?
will posted 01-29-2002 09:07 AM ET (US)   Profile for will  
I need to drill some 1.5 in holes in my Outrage's console to install some lights. Should I use a hole saw or a paddle bit? Is a good cordless drill going to have enough RPM to do the job well?
Arch Autenreith posted 01-29-2002 09:18 AM ET (US)     Profile for Arch Autenreith  Send Email to Arch Autenreith     
Paddle bit (AKA spade bits) cut holes fast but usually, if not always, splinter the wood when it comes out the other side. You can avoid that sometimes by pre-drilling from the opposite side but even then the holes are very rough. I always prefer hole saws. Much beyone 5 inches I use jig-saw.

Cordless works fine almost any size but the bigger holes just take a little longer.


LarrySherman posted 01-29-2002 09:53 AM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
Use a Forstner (sp?) bit. More expensive, but worth it.
kingfish posted 01-29-2002 10:05 AM ET (US)     Profile for kingfish  Send Email to kingfish     
Hole saws work just fine.
triblet posted 01-29-2002 10:33 AM ET (US)     Profile for triblet  Send Email to triblet     
I'd vote for the hole saw. It will be fine.

The Forstner may give a bit cleaner edge, but
that doesn't matter in this case, and they
tend to walk if not perfectly plumb with the
surface. And they are a good bit more expensive.


will posted 01-29-2002 10:34 AM ET (US)     Profile for will    
will a 12v Dewalt generate enough RPM's? Also, how closely can I drill to the corners?
will posted 01-29-2002 10:42 AM ET (US)     Profile for will    
the corners of the console?
OutrageMan posted 01-29-2002 11:04 AM ET (US)     Profile for OutrageMan  Send Email to OutrageMan     
Yes, your cordless drill will work fine. I wouldn't get any closer than 3/4" to the edge. One other idea is to cover the area to be cut (inside and outside) with masking tape to help reduce chipping.

Let the drill/bit do the work. Don't apply mch pressure.

will posted 01-29-2002 12:00 PM ET (US)     Profile for will    
thanks to all for the help. I have a post about some electronics questions that I could use some help on. Thanks again.
reelescape1 posted 01-29-2002 12:24 PM ET (US)     Profile for reelescape1  Send Email to reelescape1     
You need to use one of the newer "rotozip" type tools.
kingfish posted 01-29-2002 02:50 PM ET (US)     Profile for kingfish  Send Email to kingfish     
Roto-cutters work too, but are more difficult to control and I wouldn't recommend them to a beginner. Outrageman's advice about cutting through masking tape to reduce the possibility of chipping is good stuff.
will posted 01-29-2002 03:34 PM ET (US)     Profile for will    
another question? I am going to install these new Hella L.E.D. lights. There are no screws to hold them in place. Hella suggests clear silicone caulk as an adhesive and sealant. Do any of you have a better suggestion?
seagull posted 01-29-2002 04:10 PM ET (US)     Profile for seagull  Send Email to seagull     
3M 4200
kingfish posted 01-29-2002 06:54 PM ET (US)     Profile for kingfish  Send Email to kingfish     
Second that (3M 4200); 5200 is too permanent for my liking - you *will* pull up gelcoat if/when you want to move or remove item. 4200 will hold up for as long as you or i will be around.
White Bear posted 01-30-2002 10:29 AM ET (US)     Profile for White Bear  Send Email to White Bear     
Use a hole saw; cordless drill should be fine. As the hole saw nears the surface to be cut run it in reverse for a short while to score the surface before switching back to forward for the actual cut. This little trick will minimize chipping of the surface.
dgp posted 01-30-2002 10:57 AM ET (US)     Profile for dgp  Send Email to dgp     
Keeping on this same topic of cutting openings in fiberglass, what's the best saw /blade combination for cutting rectangular or square openings?
Tom W Clark posted 01-30-2002 12:11 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Use a hole saw. Masking tape will help as will coming at the backside (if accessible) after the pilot has penetrated the thickness of the console. Do not use a roto cutter. Starting the hole saw in reverse as White Bear suggests is another excellent idea.

dpg, The best way to cut an rectangular hole is to use a jig saw with a fine, reverse toothed blade which cuts on the down stroke. It will make a nearly chip free cut (on the surface). If your are using a jig saw with orbital action it is imperative that you turn the orbital action off so the blade is going straight up and down.

I use a barrel gripped Bosch. This is as fine a jig saw as I have ever seen. It is very important to protect the surface you are cutting from scratches. I take electrical tape and cover the foot of my saw with it. I replace the tape every time I set up for a new cut out. It does not take much of a burr embedded in the tape to leave a scratch.

The other good way to make an irregular shaped cut is to use a router (which is essentially what a rotozip is), but a real router will offer much better control and will handle a cleaner cutting bit. The limitation here is that you need room to maneuver the thing so it only works if you have a large flat area where you are making the cut.

dgp posted 01-30-2002 12:50 PM ET (US)     Profile for dgp  Send Email to dgp     
Thanks Tom!
daverdla posted 01-30-2002 12:50 PM ET (US)     Profile for daverdla  Send Email to daverdla     
I just got a Metabo barrel grip jigsaw. I tried the bosch, which is excellent, but I prefer the Metabo. Really slick blade change. Unfortunately, with the bosch, you may never need a new one.
will posted 01-30-2002 01:50 PM ET (US)     Profile for will    
guys, the feedback here is great. Thanks to all for your help.
will posted 01-30-2002 01:51 PM ET (US)     Profile for will    
1 more question, will I be able to get the 3M 4200 completely off of the gel coat if I ever want to?
kingfish posted 01-30-2002 03:17 PM ET (US)     Profile for kingfish  Send Email to kingfish     
Yep - may take a little elbow grease right down at the end; I've wound up rubbing the final residue off with my thumb, then cleaning with acetate. If you have nicked or scratched the gelcoat while removing the heavier stuff, you may have to do a little patching and/or rubbing with rubbing compound or color restorer.
will posted 01-30-2002 03:19 PM ET (US)     Profile for will    
thanks Kingfish
kingfish posted 01-30-2002 04:37 PM ET (US)     Profile for kingfish  Send Email to kingfish     
You are welcome-

Tom - you had my little heart going pitter-pat - I thought you were going to tell us where and/or how to get a square hole saw!!

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