Cutting fiberglass?

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Larry Patrick

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C Dory Year
2008
C Dory Model
23 Venture
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CD023007A808
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Sea -Jo
Getting ready to cut opening under dinette seat,tools I have are 4inch grinder with metal cutting blade,Dremmel I just bought and never used yet with a cutter head,and a jigsaw with a fine metal cutting blade.Wondering which is best to use,and how to prevent chipping,also which produces least dust? Only have a 3m mask its white the 5 dollar kind. Guess 1 14 by 14 inch opening,is no big deal fiberglass dust wise. I have cut plenty of concrete,silica dust ,not good stuff,always use a good 50 dollar respirator but cant find it. Fiberglass I don't like the idea of breathing it. Went to Lowes today,they have all kinds of 14by 14 cabinet doors on display rack,raised panel ,hickory ect. Some are composite material which they say wont holdup in condensation. Guess solid wood is best choice,then paint it white. If anyone wants doors they are $50 dollars each,at www.lowes.com
 
Out of those three choices, I'd use the jigsaw and set up a guide to make as straight a line as possible (a clamped board, say). It still won't be perfectly straight (OTOH, maybe that doesn't matter if you are putting a pre-fab hatch in). I find that the "grit" blades (sold for cutting tile, looks like a bunch of sand glued to blade) work fantastically on fiberglass and don't dull. I lay blue tape over the surface first, then strike a line right on the tape and cut through that. Of course check to see what blade might hit underneath.

If you have an oscillating tool (MultiMaster, etc.), that makes even less dust.

But, don't underestimate the dust factor! I do a few things, depending on what I have on hand.

1) Always wear good respirator.

2) If no power or vacuum, lay wet paper towels all around - the dust will somewhat land on them and "stick," then you can throw them away. If you do have a vacuum, set up the nozzle right at the tool area (I tape it in place) and if possible, have the vacuum outdoors (so the exhaust won't spread dust).

3) If in a finished space, I sometimes make a clear plastic "room" and work in that - sometimes it's just the size to put my hands and tool in; other times big enough for me to get into.

4) Goggles, Tyvek suit, and disposable gloves taped to wrists of suit (fibergass dust makes me itch).

Everyone is different, but I'd rather spend an hour prepping than a half hour (or a half year...!) cleaning up fiberglass dust.

Here is a photo from when I was getting ready to cut out for V-berth hatches. Gives the general idea. I used a jigsaw with the "grit" blade. The long "stick" was to keep the piece from falling into the hole (I rotated it as I went), and the plywood was my cutting guide. In this case I ran the saw foot up on the plywood, and just the blade to the outside of it. For a shorter/straight cut, I'd probably use something more like a 1 x 2 and run the saw foot on the fiberglass. The way I did it the blade can flex slightly, but it worked for that situation.

3_Preparing_cutting_guide_1.jpg

This is what I mean by the "grit" blade:

313tYUPB0uL.jpg
 
All of Sunbeam's beta is good. I will not grind or cut or sand FG any more without a really good filter over my nose and mouth.

The grit blade is new to me, and should be killer in a sabre saw. I graduated to an oscillating blade tool, equipped with a grit type of cutter, a Fein multimaster knockoff made by Dremel, with enough hp that I used it for many other jobs, especially sanding interior corners and fillets. Well worth the investment..
 
Agreed on the multi tool. They are handy for so many jobs around a boat, and although of course there is dust, they don't *fling* dust. I bought mine (Multi-Master) before there were "knock offs," and it was expensive, but even so I have never regretted it for a minute! I don't mind that blades are a lot cheaper now though.

Still, I used the jigsaw with the grit blade for the V-berth cutout. Perhaps a router and guide would have made a nicer cut; but I didn't have one. I did appreciate the "less dust flinging" of the jigsaw. Nothing like a spinning tool to fling dust.
 
Hello Larry,

Whichever tool you have that has the narrowest "kerf" - it will create the least dust. "Kerf" is the width of the cut made by the tool.

As others have said, I'd use the jig saw. I've never used the "grit" style blade. I've had good results using a 'clean' for hardwood Bosch blade. Available at big box stores.
Like this:
t101bf_alt.jpg


Another issue I've run into is having enough room to 'swing' the body/motor part of the jig saw when reaching the corners of the proposed opening. If you CAN swing the saw without hitting anything - great. If not, what I've done is cut the corners using a hole saw of appropriate diameter to match the curve of the corner. Like this
Bi_Metal_Hole_Saw.jpg


Then, all I have to do is make 4 straight cuts. You need to do the holesaw work before you start the jigsaw work for best results. Even if you CAN swing the jig saw, I get better results with the corners by cutting them with a hole saw - much less filing and sanding to fix the not-quite-perfect curve cut with the jigsaw. And less 'filing and fixing' means less dust.

Good luck,

dave
 
I have used many tools, on fiberglass, including Rotozip. For the most part, I use a fine cut (not metal blade), as Dave, suggests. They cut faster than the grit blade for me. Bimetal blades last much longer and are with ti. You can also vary the part of the blade which is cutting on many saber saws. I do also tape the area I am going to cut. I have always used a 3M respirator (and we did a not of cutting when fiberglass boat building)--no attachment for the shop vac, but we had the shop vac running as close to the area as possible.

Most of the cuts I have made require right angle corners than curved, so I have used a 3/8" drill bit for the hole--just inside of the line, That way, you can cut both ways, right to the point where the two lines intersect at the corner. I run the blade fairly fast, but without a lot of pressure.

When I use a hole saw it is bimetal also. I still have some hole saws left over form 40 years ago which are still usable. My smallest hole saw is 5/8" of an inch--largest is 6". To find the place to put the 1/4" pilot bit with the
saw, I draw right angle lines with a square and start the hole where they intersect--each the same distance out from the straight side line, as the total width of the hole saw.

One other thing to remember, wear a disposable Tyvek suit, and a "Sock" over your head, and googles (not just glasses) to keep the particles out of your eyes.

For small cuts I have found that the Fein type of saw works great, but the blades I have had don't seem to hold up as well as the saber saw blades, and the cutting seems a bit slower--but I have not used it as much, so it may be my technique. If the glass was real thin, then I would definitely use the Fein type. (I also have the fake Dremel type, and so far it has done OK).
 
I tried a metal cutting blade when I cut my v berth. I wanted a fine tooth cut. However, the metal blades did not last very long. Blades for hardwood worked much better.
 
Thanks everyone,will tape it,didnt think of that. Also googles ,was going to use safety glasses, googles makes more sense .Tyvec suit hadn't thought of that good idea. Shop vac should help with dust,this is my first time cutting fiberglass.
 
I haven't found a good style of blade yet. For just fiberglass, metal worked best, but they would have rounded teeth after about 48". I just cut hatches in my berth and needed to cut through 1" ply with fiberglass on both sides. Metal was really slow. I used a wood blade, and I used lots of them. It took me three blades to cut out a 9 x 24" hatch. So my choice of jig saw blades is "lots of them." A ten pack is what I suggest.

Mark
 
Marco Flamingo":2rfqitbi said:
I haven't found a good style of blade yet. For just fiberglass, metal worked best, but they would have rounded teeth after about 48". [snip]
Mark
Click to expand...
Mark, Scroll up to Sunbeam's post. The blade she shows has a coating of coarse grit, which does not wear when cutting fiberglass. That will take you through the glass. You may need to go back with a conventional metal blade with crosscut metal teeth to finish the plywood interior.

A tool like the Fein Multimaster is even better because the blade oscillates back and forth, but Fein tools are very expensive. https://www.youtube.com/watch?v=f8uWoT5XJdw In lieu, consider one of the Dremel knockoffs, called the MultiMax. I used one of these on a large FG job, and it really performed well. This is one of the most robust versions: http://www.amazon.com/Dremel-Multi-Max- ... ting&psc=1
 
I always just use my teeth! Seriously, there are lots of ways to do it and the dust is horrific. I often duct tape my shop vac hose right next to where I'm working and it sucks most of it up.
 
I bought the "grit" blade I'm using now in around 2007, and I have cut a lot of fiberglass with it since then! Still eats right through it like it was hungry (but very controllable). I liked it so much I bought a second one a few years ago, intending to switch to it when the first one got dull. Still waiting. It must be magic grit :mrgreen:

I do sometimes use the Multimaster, and it also cuts fiberglass very well, but when I'm making a longer cut, or a curve, I "go to" the jigsaw with the grit blade. Of course the MM fits in places a jigsaw never could, and does all kinds of other tricky cuts. So I like having both.
 
Sunbeam those blades sound good.
 
You all may think I'm nuts, but to keep the dust down I use a hacksaw blade after deelpy scribing the "good" side of the cut. I hold a vacuum under the cut and suck everything up as it is created.

I don't want to propose that this is the most effective and expedient means of cutting, but the cleanest and, for me, worth the time.

http://static.grainger.com/rp/s/is/imag ... 1?$mdmain$
 
I don't think that's nuts at all. I have done the same in order to avoid dust -- especially at times when I had no vacuum/power and used damp paper towels spread around as dust-catchers. Anything to avoid fiberglass dust flying around!
 
Hell, no, you are not nuts, Kushtaka. Way easier to contain the debris as you generate it, in lieu of cleaning up later. I stick a shop vac nozzle near everything I can.
 
If you want to manually cut using this type of hacksaw blade, I came across a single blade holder, which has a fully cushioned handle--and is a lot more comfortable to use than the one pictured. (Sometimes you find things you bought 10 years ago, and forgot you owned when cleaning out the garage every 15 years or so!)

I don't see it in the current catalogue. It does not have the "D" part--half a blade just fits in the handle. The handle is similar to the Milwaukee handle pictured:

49698_48-22-0012-lg.jpg
 
I have one that may be something like you are talking about. I'm pretty sure it's a Stanley Fat Max. Shown with reciprocating saw blades but will hold hacksaw blades too (presuming that is the one I have; I think it is). The bad part is that of course the blade can billow out to the side (as it's less supported than the D-shaped handle. But to the good, you can take much longer strokes, which would be handy in this type of application. Beats wrapping tape around the end of the blade (although that does tuck nicely into the toolbox).

I haven't tried it with a reciprocating saw blade yet - only a hacksaw blade.
 
I used one of the grit blades in a jigsaw to cut some 1/4" G-10 fiberglass board this summer. It worked surprisingly well. Did it outdoors, wearing a painter-type mask with good 3M filter, and with the shop-vac running by the cut. G-10 is much heavier than the glass in the decks of the C-Dory, and I was making a backup plate for my anchor windlass.
 
Finished project cutting fiberglass, the 14 by 14 cabinet door from Lowes was too big. Bought a cut off birch lumber core plywood 1/2 inch 30x30 inch $7.00 AT lowes cut out a 13.5 by 11 inch piece to make door. Routered edge and groved out a finger grab. Boat was in shop when I asked info about cutting opening,so just got around to doing project. Two hinges ,and plywood on inside to anchor screws in. Now convient to open and get stuff without taking seat off. Little things like this make the wife happy.
 
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