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Old 26-06-2012, 09:53   #61
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Re: Cure for Plexiglass / Lexan Crazing?

Sorry, like I said after reading all the posts I was in a blur. For cast acrylic on a blue water boat where the length is 57" and the height is 7" what would you suggest the thickness be?
Thanks for the patience,
Mike
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Old 26-06-2012, 10:00   #62
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Re: Cure for Plexiglass / Lexan Crazing?

" For cast acrylic on a blue water boat where the length is 57" and the height is 7" what would you suggest the thickness be?"

It is not just the size, Mike. Consider this: You spinnaker pole gets loose during a gybe and becomes a 16-foot-long javelin aimed right at that port. You think quarter inch plexi is going to stop it?

You need to evaluate the possible impacts on your boat, from "crew fell down" to "20' wave broke over the bow" and factor them in. Arguably the glazing should be as strong as the surrounding hull area and that's sufficient. And, of course, the glazing has to be set and mounted properly to move and allow it to flex and take strains and impacts.

If I had to pick a random number without further guidance, maybe 3/8 would do.
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Old 04-07-2012, 14:38   #63
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Re: Cure for Plexiglass / Lexan Crazing?

Quote:
Originally Posted by Cheechako View Post
"Remember the coefficiant of thermal expansion for Acrylic and Polycarbonate is in the neiborhood of .000039 per inch per degree F. That means an 8ft plastic port will expand and contract up to 1/2 of an inch from the coldest day in Feb to the hottest day in summer."
I'm only getting .0234" change per 10" length.....? (30 degrees to 90 dgrees)
0.0234" per 10" expansion over 8'-0" equals about a quarter inch with a 60 degree delta. For increased delta, 1/2" seems quite possible. Variations in measurements might easily equal 10%. However, the 0.0234"/10" expansion rate seems, of itself, to be problematic in many installations.
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Old 04-07-2012, 18:53   #64
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Re: Cure for Plexiglass / Lexan Crazing?

At 0.000039 per inch time 96 inches, and a temperature swing from 30F (easy winter day) to 110F (heatwave) that's about a 0.29" change, but remember that surfaces exposed to direct sunlight often get hotter, i.e. 140-160F so a movement of 1/3" is certainly within the relam of likely.

Any reputable glazing supplier will have engineering diagrams available on the web, showing correct and incorrect installation schemes to use for their products, allowing for thermal expansion and waterproofing. The bottom line is that the glazing MUST be free to move, and sealed in a way that allows it to move past the seals, or it will be damaged by ordinary thermal movement and other stresses.

In a boat (or simply a portlight) "built to a price" the builder may not care if the glazing crazes or leaks in ten years, by then it is someone else's problem. But the problem, and the answers, are extensively documented.
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Old 15-09-2012, 14:56   #65
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Re: Cure for Plexiglass / Lexan Crazing?

FOR CRAZING ON PLEXIGLASS ETC:
everyonehas old tubes of toothpaste they dont like-- go get one. then goget a soft cloth.
put toothpaste on cloth and rub circles on the windows--like buing your porsche..or bmw, or mercedes......
rinse with water on a soft cloth......

so i will be redoing my windows with toothpaste making a nice clear center fading to translucent edges....
is safety feature at no extra charge---if in cabin, one must be able to see out without giving self away......




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Old 15-09-2012, 15:32   #66
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Re: Cure for Plexiglass / Lexan Crazing?

Quote:
Originally Posted by zeehag View Post
FOR CRAZING ON PLEXIGLASS ETC:
everyone has old tubes of toothpaste they dont like-- go get one. then go get a soft cloth.
put toothpaste on cloth and rub circles on the windows--like buffing your porsche..or bmw, or mercedes......
rinse with water on a soft cloth......

so i will be redoing my windows with toothpaste making a nice clear center fading to translucent edges....
is safety feature at no extra charge---if in cabin, one must be able to see out without giving self away......




sorry--i couldnt finish editing before wifi kicked me out--is now done..thankyou for patience.
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Old 15-09-2012, 16:44   #67
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Re: Cure for Plexiglass / Lexan Crazing?

A traditional "tooth polish" toothpaste, like original Crest, is mainly diatomaceous earth (aka Fuller's earth) which is also sold as a mild abrasive. That's great for polishing plastics, it is something like a 1500-2000 grit abrasive.

However, the "gel" toothpastes are not the same. And some of the "whitening" toothpastes and other fancy types will actually attack or scratch plastics. Which is why original Crest is often recommended, by name, for plastic polishing.

As for crazing, that's cracks in the plastic. No toothpaste in the world will help cure those.
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