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Old 04-06-2009, 15:27   #1
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Curved Pilothouse Window Hell!

Hi all! Just thought I'd strike up a conversation on pilothouse window construction. Several different boats (Cats, Pilothouses, Trawlers) use curved corner windows like ours. Replacing ours has turned out to be alot of fun! NOT! This is just a quick update. If anyone has any actual experience with this, I'd love to hear from them. So far, we have home-built an oven, moved it up to the foredeck and we are currently testing samples before we actually attempt to bend a real, 3/8" thick 320 deg F $150+ piece of grey tinted Makrolon. Tests have been positive, but tolerances are much closer than I originally imagined. Attached find a pic of where the corner windows will go. They are attached by thru bolting them along with an aluminum outside bezel. This is a real adventure!
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Old 04-06-2009, 15:38   #2
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I don't envy you the glass-bending task ahead, Chris, but it looks like you did a nice job on the front window so I'm sure the results of your efforts will be excellent. Look at it this way, you may soon have the market cornered on replacing curved boat glass - Wheeeeeeeee! BIG $$$$.

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Old 04-06-2009, 15:44   #3
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Look at it this way, you may soon have the market cornered on replacing curved boat glass - Wheeeeeeeee! BIG $$$$.

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Not GLASS! LEXAN and PLEXI!
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Old 04-06-2009, 15:46   #4
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Bending windows

I'd figure the radius or bend needed and than bend an oversize piece to that radius, then trim it to fit, instead of trying to cut the perfect shape flat and hoping it would fit after I bent it. I hope that's what you're trying to do Chris. Trying to lay that out and cut it flat so that it fits after you bend it strikes me as an exercise in frustration, but then there are quite a lot of exercises in frustration in boat building... good luck.

Best, Bob S/V Restless
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Old 04-06-2009, 15:53   #5
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Not GLASS! LEXAN and PLEXI!
Well, yes, of course - but I use glass in the same way the things we drink out of on boats are "glasses," even though they're plastic.

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Old 04-06-2009, 17:17   #6
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Oh sure Tao! Everything always come back to drinking with you sailors! As for Bob's suggestion, where were you 3 months ago! Nope, I made patterns, a bending jig, and drilled registration pins instead, as I believe in making this as hard as possible! I'll post pics of the homemade oven and jig soon, along with several trashed pieces of Lexan...
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Old 04-06-2009, 19:46   #7
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So, let's talk about an issue with lexan/makrolon (polycarbonates) : the coatings available.

Our Lexan XL 10 has an UV coating with 10 year warranty... but you loose that warranty when you touch it like washing the windows. This material is meant for use in roofs like shopping malls, stadiums etc. So, we wash them anyway... result: can't see anything through them after a couple of years.

So, I investigate, send emails to manufacturers etc. and they tell me that I should use Lexan MR10 or equivalent. GE gives a 10 year warranty on both UV and abresion. Bayer makes Makrolon and have a similar coating but no written warranty, Sheffield doesn't have it at all, so we go for GE MR10. I ask for quotes and they tell me that minimum quantity is 30 sheets. 8'x4' sheets that is. Like if I'm going to glaze a skyscraper ;-)

Also, you can NOT make curved windows with MR10 as this process will break the coating. But we are blessed and only have flat panels.

So, no MR10 because I can't buy a small quantity. Now what do we do... we wet-sand, first 330 grit followed by 500, 800, 1200 and 1500 grit. Now we switch to rubbing compound and the Makita polisher, followed by polishing compound. Result: perfectly clear windows that will turn back to opague in weeks. We are now doing it all again and finish with one of those new high tech coatings like 303 aerospace protectant (we use something similar from that CorrosionX company). We'll see how it holds up but the first windows are still clear after a month.

Also, we meet other boats that have shiny new MR10 windows which they had done by yards in the US. As I don't believe these yards buy 30 sheets, there must be better sources.

Question: anyone knows a source for GE Lexan MR10 3/8" or 1/2" thick, grey colored?

ciao!
Nick.
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Old 04-06-2009, 20:30   #8
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Nick! You've experienced window hell too! I almost bought Makrolon AR, which has the coating... I would have been sorry now! I bought 2 - 3/8" Makrolon sheets from Northeast Plastics in Philadelphia: Northeast Plastics Supply Company This stuff aint cheap! I have only used Plexus on windows and hatches: Plexus Plastic Cleaner
It's the only thing that touched my Cessna windshield too. BTW, I stole my mounting technique from Dashew's Cruising Encyclopedia. You can appreciate that!
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Old 05-06-2009, 00:31   #9
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Good luck. I have heard of people using felt covered forms to bend plexi onto to a particular curve. Any chance the originals were cold formed or is the curvature simply too great?
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Old 05-06-2009, 04:10   #10
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... Question: anyone knows a source for GE Lexan MR10 3/8" or 1/2" thick, grey colored?
The first 3 returns on a Google searcch < GE Lexan MR10 >

Polycarbonate Lexan MR10 UV Stabilized Sheets
Polycarbonate Lexan MR10 UV Stabilized Sheets

LEXAN® Polycarbonate Sheet (MR10) by Piedmont Plastics, Inc.
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Old 05-06-2009, 05:50   #11
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I have heard of people using felt covered forms to bend plexi onto to a particular curve. Any chance the originals were cold formed or is the curvature simply too great?
Hey Evan! I actually don't have the originals, but there is no chance, as the cold forming minimum radius for this thickness is over 20 times larger than what we need here! I did learn about the felt covering though, and we're using it. This type of forming is called "Drape Forming"...
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Old 05-06-2009, 08:28   #12
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Maritime Plastics in Annapolis will sell you as little or as much LExan MR 10 ( and any other Lexan/ Acrylic product) as you need, down to one square foot.. THey will aslo bend it for you
www.maritimeplastics.com
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Old 05-06-2009, 11:24   #13
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Curved Windows are Hell!. I could not agree more. They're great at boat shows and in brochures and that's all. As I have recently discovered, this a case of form over function. For gods sake, we're a boat, we do 6 knots, designing windows to maximize the critical Mach number is nuts. I'm still wrestling with getting replacements made up. No option is without its "issues" (code for $$$) .
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Old 05-06-2009, 11:48   #14
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curved windows

Chris, sorry I couldn't get back to this until now. Although I'm sure it's possible to do it the way you're proposing, there are 2 problems that I can see with that approach... the first is that you will probably have difficulty getting curvature right out to the edge, if that's what's called for, unless you are pressing into a form (female) with a shaped (male) punch type thing, both of which fit together perfectly less the thickness of the material. The other is that to cut the material flat and have it come out to the right dimensions after the curve, you have to figure out what the dimensions should be along the neutral axis of the material, which is generally considered to be .44 times the material thickness. The neutral axis is the path in the material that is neither compressed (inside) or expanded (outside). It's a common problem in bending or rolling metal, and you can find out a lot by googling bend allowance.

It's for these reasons when making one offs that I generally find it easier to just make the thing oversize, get the curve right, and then trim to fit. If you were setting up to make a hundred of them, then it would obviously be worth getting the pattern and bend allowance correct, but for one offs not so much.

Good luck with it, it can be done but will be a bit of a struggle.

Best, Bob http://www.sv-restless.com
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Old 05-06-2009, 11:54   #15
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an interesting note regarding Lexan vs regular poly is the lexan has visible ripples/distortion in it. I'm really not sure the abrasion resistance is that much better either....
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