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Old 25-04-2009, 09:47   #1
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Cutting a hole in my deck hatch

I am going to install a solar powered vent fan in one of my deck hatches. It is a Lewmar, and I beleive it to be acrylic. Does anyone have any tips on cutting a 4.7'' hole into this material, as I understand it tends to melt when heated?
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Old 25-04-2009, 11:07   #2
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I used a hole saw to cut the mounting hole for my Nicro solar vent. Just take it easy and don't put too much pressure on it, and all will be fine. Don't know if you can find a 4.7" hole saw, but it would be worth looking for one. The other option is a jigsaw. I've successfully cut acrylic mirror material with one. Use a new (sharp) blade designed for plastic, and skinny enough to make cutting the circle easy. Again, the key to success is to take it easy and let the saw do the cutting without much pressure. Tape the plastic to keep from scratching it with the shoe of the saw.
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Old 25-04-2009, 11:27   #3
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I haven’t done this so take this advice for what its worth.
I think I'd drill a hole and then use a variable speed jis saw at a fairly slow speed.
Take care to protect the plastic from being scratched by the bottom (table) of the jig saw.
This can be done by putting masking type tape on the table or on the hatch.
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Old 26-04-2009, 06:50   #4
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A properly sized Hole Saw, operated a slow speeds, is the preferable cutting method.
If unable to find a good fit, in a hole saw, try an adjustable beam circle cutter. Again slow speed, and slow feed.
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Old 26-04-2009, 12:13   #5
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I'd have to agree with Gord May.

A fly cutter might be your best bet. Again let the cutting bit do the work, not speed of pressure, to avoid heat.
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Old 26-04-2009, 12:57   #6
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Ooo wee . That looks lethal.

There is another option. I may be wrong because of the heat issue, but if you go slow this should be OK.

I have a RotoZip on board (side cutting tool like a miniture router or a dremel on steroids). I bought the hole cutting attachment, which is basically a compass sort of set up. Cuts perfect holes everytime reasonably fast without dangerous spinning things (in my opinion).

I cut fiberglass with this thing with ease, once I got my hands on the right carbide tipped bit. I also bought the right angle attachment for it to turn it into a grinder.

But wait there's more.................

Seriously, I quit carrying a lot of other tools because this one does so much. And large diameter holes are one of the things it does best. I always try to push the tool with my vacuum hose. Keeps the mess way down.
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Old 26-04-2009, 15:07   #7
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If you are going to cut a hole of any size with a fly or beam cutter bring the part to a drill press, it would be very difficult with a hand drill.
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Old 26-04-2009, 15:14   #8
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drill press

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Originally Posted by stevensc View Post
If you are going to cut a hole of any size with a fly or beam cutter bring the part to a drill press, it would be very difficult with a hand drill.
Steve
I thought about that after I posted my thread. One more advantage of the side cutter(RotoZip). You can do it in place.

Sometimes I sound like a salesman to myself. Did I mention that I have accomplished a lot of heavy jobs with this thing?
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Old 26-04-2009, 16:58   #9
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Agreed...

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If you are going to cut a hole of any size with a fly or beam cutter bring the part to a drill press, it would be very difficult with a hand drill.
Steve
But I would go further and say a fly cutter can ONLY be used in a drill press, certainly at the diameter in question. If it snags, someone is getting hurt.

I sort of feel the same way about the hole saw, or at least that the results would be better with a press. Try to find a friend that will drill the hole for you. Better, get a modest drill press. If you invested in a boat, a drill press is on the short list of valuable and versatile power tools. You'll get better results.
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Old 26-04-2009, 17:16   #10
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Hummmm,

Let me see.... Remove the hatch & buy a drill press or buy a handheld tool and do it in place, which will also give you a "better result".

I can't tell you how many 4" and bigger perfect holes I have cut in boats with this thing. All done quickly, cleanly and in place, for a lot cheaper than the cost of a drill press.

I would love to have a drill press. Can't say that it would get that much use and it would certainly not have been justified as something I would have fit into my boat when I dropped the dock lines.

When I was a kid I went hunting for rabbits once with a shotgun. We didn't see any, but there were bales of hay that I knew had mice under them. We started kicking them over and shooting the mice with 12 gauge shotguns from 10 ft away.

You can do it the harder, time consuming and more expensive way if you want. The result will not be any better.
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Old 26-04-2009, 17:43   #11
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This is the sort of job that if I had to buy any special tools to do it or had any concern about doing myself I would just take the lid to a plastics fabricator or trusted boat yard and get them to do it.

Probably 1/4 hours labour tops and if they stuff it up it is their problem (very unlikely to happen given the practice they will have had on others) so it seems a no brainer to me - unless one is inclined to being adventurous in such things, of course.
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Old 26-04-2009, 18:12   #12
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I have had a Rotozip for several years now it is a very useful tool.
Steve
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Old 26-04-2009, 18:17   #13
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Remember that the hole can be a little larger than the fitting that drops in, as long as the finish ring covers the hole enough to allow fasteners and caulking to do their magic, therefore 4.7 inches might be substituted by 4.75 inches. Also, are you talking about cutting through the acrylic or Lexan hatch, or is it fiberglass? You might consider "flame polishing" the edges of a hole in acrylic to relieve the stress caused by the chipping action of the hole saw teeth. If drilling holes for fasteners in acrylic, consider a plexiglass drill bit, it as a sharper angle that helps to reduce cracks later on. Also, don't neglect the possibility that a reinforcing ring or pad glued onto the underside of the cutout, will help increase the strength of the hatch that has had a hole cut in its middle section.
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Old 26-04-2009, 19:05   #14
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OK, I have to agree about the "in place" point.

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Hummmm,

Let me see.... Remove the hatch & buy a drill press or buy a handheld tool and do it in place, which will also give you a "better result".

I can't tell you how many 4" and bigger perfect holes I have cut in boats with this thing. All done quickly, cleanly and in place, for a lot cheaper than the cost of a drill press.

I would love to have a drill press. Can't say that it would get that much use and it would certainly not have been justified as something I would have fit into my boat when I dropped the dock lines.

When I was a kid I went hunting for rabbits once with a shotgun. We didn't see any, but there were bales of hay that I knew had mice under them. We started kicking them over and shooting the mice with 12 gauge shotguns from 10 ft away.

You can do it the harder, time consuming and more expensive way if you want. The result will not be any better.
For some reason - no good reason - I thought it was out of the boat. I would certainly do it in-place.

I have used a roto-zip - not for this - but it sounds right.

The drill press still belongs on the short list. You will find very few shops without one, and there are about 500 reasons for this.
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Old 26-04-2009, 19:21   #15
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You could try a holesaw as large as you can get and then use a router to finish to the proper size. Do it a small section at a time to prevent over heating of the plastic and have a honking big shop vac on hand to suck up the shavings.

Make up a circular guide from fiber board that would be the diameter of your desired hole, plus the diameter of your router base. Then subtract half the diameter of your cutter. IE .375 for a 3/4 inch cutter.

For example. You want a 4.7 inch hole. Your router is 6 inch in diameter. the hole would be 10.7 inches in diameter and if you were to chuck a scribe into the spindle it would scribe a circle 4.7 inch in diameter.But your cutter is 3/4 so you must subtract .375 from that diameter down to 10.325 inches.
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