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post #1 of 13 Old 01-07-2008 Thread Starter
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Cutting through hole

I got a Dickinson Newport propane heater for xmas. I'm trying to decide where to put it. There is a nice spot in the cabin for it where there is already a hole for the chimney. The hole is currently occupied by a nonworking solar fan. However, the recommended minimum chimney length is two feet. The chimney length in this spot would be closer to one foot.

There is another spot in the cabin where it would look even nicer, and the chimney length there would be at least two feet. However, I would have to cut a new hole for it. I've never cut a hole in fiberglass. The hole diameter would be three inches. If I put the chimney there, how would I go about cutting the hole? I have a portable drill on board and a bunch of other tools. The only saw I have is a hacksaw, but I suppose I could borrow or buy the appropriate saw.

I was thinking of drilling multiple small holes around the perimeter of the large hole, cutting between them and then filing for a measured regular circle. I've done this in other materials. Is there a better procedure when working with fiberglass?

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Scott
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post #2 of 13 Old 01-07-2008
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Buy a hole saw for the drill. Simply nothing else works better and you can now buy the lower-end hole saws for less then $12 a set.



When using them, drill/saw most of the way through the GRP, then around to the other side, thread the centre biyt into the pilot hole and finish sawing form the other side, this gives you clean edges on both sides without any gelcoat popping off the edges.


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post #3 of 13 Old 01-07-2008
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A holesaw is the way to go. It would be the best tool for cutting a proper hole. They do make adjustable diameter hole saws, but if it is a standard diameter, a regular hole saw should do the trick. Hole saws have a central arbor that you set at the centerpoint of where you want the hole cut.

A three inch diameter hole saw will require a fairly powerful drill.

BTW, if you run the saw in reverse initially, you won't chip the gelcoat as much... then once you're through the gelcoat, switch the drill to forward operation. The idea of using the holesaw from both sides is also an excellent one, and I'd recommend it.

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post #4 of 13 Old 01-07-2008
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Hole saw!

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post #5 of 13 Old 01-07-2008
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One word of caution: when you start boring your hole it is likely the hole boring bit will grab the material (your cabintop in this case) and jump out of control, skidding along the deck and making a mess. To avoid this start drilling, slowly, and at a slight angle to your cabintop. This way only a small portion of the bit is cutting. Slowly revolve the bit around a full revolution until you have gone all the way around. Then you can drill more vertically, although you may still find it easier to keep it at a slight angle.


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post #6 of 13 Old 01-07-2008 Thread Starter
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How hard is it to cut through fiberglass? I've used drill hole saws for cutting doorknob holes and such, but a three inch hole is quite large. I've done the procedure I describe above for cutting larger holes.

Also, my portable drill is probably underpowered if the material is hard. But I'm at a marina, and could probably borrow a cord drill.
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post #7 of 13 Old 01-07-2008 Thread Starter
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Thanks. Sounds like a good technique. It's quite a large hole for a hole saw, and I'm sure it's going to be quite a pain.
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post #8 of 13 Old 01-07-2008
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Not all that hard... you will want a corded drill or a very powerful cordless unit though.

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Yeah, it's wicked easy. An underpowered drill will probably just take longer.


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post #10 of 13 Old 01-07-2008
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Or you will burn out the drill. Also try a pilot hole one size smaller than the pilot bit in the hole saw
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