How to (jig)saw fibreglass?

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neil1967

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I had two speakers in poor condition mounted in the cockpit coaming of my yacht. I removed them and want to put small cockpit lockers/boxes/cubby holes in their place, which will necessitate enlarging the holes left by the speakers. I have done one side but managed to wear out two new jigsaw blades cutting a single hole about 12 x 15 cm 'square'. The fibreglass is about 8mm thick. I have the other side still to do - what are the best blades to use and is there any particular technique (cut slowly? cut fast) or do I have to just accept that glassfibre is tough and I will wear out the blades quickly?
 
For round holes I use a hole saw. For square holes I use an angle grinder with a diamond impregnated blade (I think they are also used to cut tiles). For square or oblong holes with rounded corners I use a hole saw in each corner and join up the corers with the angle grinder. The angle grinder blade has lasted 20 years now but I am on my second angle grinder (and I use it a lot).

I have never found jigsaws give a neat finish. too much chipping.

Jonathan
 
Drum sanders and flap wheels are dead handy for enlarging such holes, it's a doddle to do a nice neat job on thin GRP. 8mm will be a bit more tedious.
Because they sand along the edge, they don't chip or fray the edge.
I would do what you can with an angle grinder then clean up with a drum sander in a Black and Decker drill.
A padsaw may also be useful.

You might use a diamond tool in a Dremel to go around the gelcoat, then use the jigsaw for most of the bulk?
 
Buy special jigsaw blades coated with carborundum - no teeth. Not fast, but do a good job and don't go blunt.
 
Agree with previous advice, carborundum tile jigsaw blades or angle grinder.
Wear a mask and googles and overalls. It's itchy stuf and floats everywhere.
Stating the bleeding obvious, it's a good idea to drill a hole in each corner and cut into that, then tidy the corner with a file or jigsaw
 
In re itching: i've not done as much GRP as some people, more than some, but I can't face it now, just the thought of grinding it gives me the itch. I note the Hayle boatbuilder has used paper suits taped up for many years.
 
fisherman said:
In re itching: i've not done as much GRP as some people, more than some, but I can't face it now, just the thought of grinding it gives me the itch. I note the Hayle boatbuilder has used paper suits taped up for many years.
Click to expand...
Epoxy can be among the worst things.
One bloke built a veneer/epoxy 505 dinghy and ended up so allergic to it, he couldn't sail it despite it being painted and varnished.
Then again, just looking at fibreglass loft insulation on the Wickes website makes me itch.
 
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