Curved cabin rooflights replacement

[Bill O]

The difficulty here is over thinking the project and mentally stalling, when it is most likely a straight forward job, simple job.
Take out the old window, then see what you have, then determine thickness and tint (bronze?) you need. Once you do this you will most likely find its a flat panel bent to fit.

Don't know where you are located but there has to be a plastic distribution or someone selling plexi near you

[krivanj]

We have had our 9.2 since 1985 and replaced the side windows twice on each side. Once the plexiglass is cut, the mounting is so flat, there is no bending of the plastic to do. All those small screws hold it fast without an initial bend.

[n5ama]

It's like you said, almost no bending. I does appear to have gotten a little "set" probably because it's been in place so long but it's easy to flatten and use for a pattern to cut and drill.

[krivanj]

Each side is made from two plexiglass parts with a vertical seam in the middle. That alone lets it be relatively flat. No bending.

I'd like to find a pattern before I take them off to replace them. The plexiglass lasts about 10 years and then teh sun gets it. Time to replace them again.

[n5ama]

Took awhile but I finally got around to purchasing the Lexan. It was purchased from Granger's Supply and got in yesterday.

I guess the question now is how best to cut this stuff. I'll pull the old rooflights and use them as a pattern. I plan to use double sided tape between the sheets and in the middle to attach them before I make the cut. I have a large bandsaw (20") but I know cutting plexiglas on it causes the plexiglas to heat up, melt and reform on the back side of the cut about as fast as you can feed it. Does the Lexan do the same or is there a better way to cut it?

I'm open to suggestions. I bought enough to make some test cuts.

Thanks,
Tom

[BigNut]

If you have a steady hand, an oscillating saw works well.

[Allied39]

Absolutely doable but requires more thought than "heat with hair dryer"

Therma forming acrylic possible. Lexan, or actually polycarbonite is not really possible as it dis colours when heating to the temps required for it to hold its shape IE around the 220f area.

Initial success is often short lived when crazing appears due to lack of adequate heat and reduction of heat too quickly.

All depends on actual required bend and fixing and obviously material thickness, and I dare say, whether the material requiered is acrylic or polycarbonite.

This post for the OP, i do not care to argue or deal with the trolls present

[n5ama]

The material I have is acrylic, it's 0.118" thick and appears to be way more flexible than I need to match the curve.

I think my major problem will be cutting a decent edge on the new material. Sawing this stuff has me nervous. I should be able to either file or grind a decent edge on it if I don't booger the edge and generate stress cracks back into the sheet while cutting.

As mentioned before, I have cut some thicker plexiglas and the material melts and reforms on the backside of the saw blade as fast as I made the cut.

If I can successfully cut, dress the edge and drill to the pattern of the old piece, could I use butyl tape to seal?

Thanks for the help!!!

[stormalong]

Originally Posted by n5ama

The material I have is acrylic, it's 0.118" thick and appears to be way more flexible than I need to match the curve.

I think my major problem will be cutting a decent edge on the new material. Sawing this stuff has me nervous. I should be able to either file or grind a decent edge on it if I don't booger the edge and generate stress cracks back into the sheet while cutting.

As mentioned before, I have cut some thicker plexiglas and the material melts and reforms on the backside of the saw blade as fast as I made the cut.

If I can successfully cut, dress the edge and drill to the pattern of the old piece, could I use butyl tape to seal?

Thanks for the help!!!

You can cut this on a bandsaw. Cut very slowly with a good blade and there should be no problem. Cutting fast or with a dull blade causes it to heat up. Cut it a bit larger and use a hand plane to get it down to size and get a smooth edge. .118 is just under 1/8th of an inch - not difficult to cut but also not very strong. I use 1/4 inch on my long(ish) fixed lights that are about 5 inches wide at their maximum. Also, when drilling the screw holes use a sharp new bit turning as slow as you can to prevent heating and cracking the plastic - a drill press works much better for this than a handheld electric drill.

Suggestion about installation. Leave the paper on the plexi. Hold it into place and outline the opening size with a pen. Peel back the paper and cut to the line. With the paper still protecting the see through part of the window lightly sand the portion to be bedded. The roughened surface will bond to the sealant of your choice much better than the smooth surface. Leave the paper on until you have installed the light and cleaned up the sealant. This makes the cleanup much easier. One more point. After you have the paper cut to size on the plexi lift the edge in a couple of places and put some of the paper under the edge to make tabs to easily lift the paper when the install is done.

[guyrj33]

soapy water is a good lubricant and coolant for cutting Plexiglas. The cut edge can be sanded smooth and made clear by applying alcohol to the edge and lighting it on fire.

[n5ama]

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Originally Posted by stormalong

You can cut this on a bandsaw. Cut very slowly with a good blade and there should be no problem. Cutting fast or with a dull blade causes it to heat up. Cut it a bit larger and use a hand plane to get it down to size and get a smooth edge. .118 is just under 1/8th of an inch - not difficult to cut but also not very strong. I use 1/4 inch on my long(ish) fixed lights that are about 5 inches wide at their maximum. Also, when drilling the screw holes use a sharp new bit turning as slow as you can to prevent heating and cracking the plastic - a drill press works much better for this than a handheld electric drill.

Suggestion about installation. Leave the paper on the plexi. Hold it into place and outline the opening size with a pen. Peel back the paper and cut to the line. With the paper still protecting the see through part of the window lightly sand the portion to be bedded. The roughened surface will bond to the sealant of your choice much better than the smooth surface. Leave the paper on until you have installed the light and cleaned up the sealant. This makes the cleanup much easier. One more point. After you have the paper cut to size on the plexi lift the edge in a couple of places and put some of the paper under the edge to make tabs to easily lift the paper when the install is done.

It sounds like you have “Done There - Been That”! I appreciate you sharing your experience/technique with me.

I plan to get a new fine tooth blade for my band saw. I probably won’t have much option for the kerf on this blade and if I do, I suppose I would need the widest kerf available to reduce the tendency for the plastic to flow back behind the cut. I’ll try a scrap piece to determine how fast I feed the material for the cut.

Is there a better sealant for these fixed windows than the butyl tape?

Thanks again!

[n5ama]

Originally Posted by guyrj33

soapy water is a good lubricant and coolant for cutting Plexiglas. The cut edge can be sanded smooth and made clear by applying alcohol to the edge and lighting it on fire.

I never thought about heat or flame to a cut edge. I’ll try that on a cut scrap.

Thanks!

[Northbound44]

Originally Posted by n5ama

The material I have is acrylic, it's 0.118" thick and appears to be way more flexible than I need to match the curve.



I think my major problem will be cutting a decent edge on the new material. Sawing this stuff has me nervous. I should be able to either file or grind a decent edge on it if I don't booger the edge and generate stress cracks back into the sheet while cutting.



As mentioned before, I have cut some thicker plexiglas and the material melts and reforms on the backside of the saw blade as fast as I made the cut.



If I can successfully cut, dress the edge and drill to the pattern of the old piece, could I use butyl tape to seal?



Thanks for the help!!!

You can do a better cut by using a jigsaws blade designed for plexiglass and available at Homedepot or other hardware store.

https://images.homedepot-static.com/...bf-64_1000.jpg

You can also get a better professional finish in two steps, first, by cutting your window a little bit larger than the original with a jigsaw, then, by using a router with a flush trim bit with the original old window as a guide, you can produce something comparable to the original finish.

Using butyl tape to seal the windows is a popular solution to seal them as long as you can compress it with a metal frame.
Another option would be using silicone (Dow Corning 795) or double sided tape.

[stormalong]

Originally Posted by n5ama

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Is there a better sealant for these fixed windows than the butyl tape?

Thanks again!

I used GE Ultraglaze 4000 (I think). Did this quite a few years ago and others may have better choices. The GE stuff was a trade industry product and may not be easy to get.

[n5ama]

Originally Posted by stormalong

I used GE Ultraglaze 4000 (I think). Did this quite a few years ago and others may have better choices. The GE stuff was a trade industry product and may not be easy to get.

Thanks, I ordered a tube from Amazon.
A tube costs about $16 shipping included.
The 4000 sounds like it will work well. I’ll
be careful when applying this stuff to avoid
a lot of “squeeze out“. It’s black and wouldn’t
look good on the exterior white gel coat.