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Old 07-02-2007, 05:45   #1
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Lexan Question

The Lexan on my companionway is crazed and I am planning to get around to replacing it but I am not comfortable with how much the plastic is crowned or curved and because it's 5/8" thick, reproducing this shape worries me. I am not sure it's actually lexan because of the way it's crazed and even considering it is 20 years old I suspect the material is plexiglass. I am considering making up a form and heating the material to allow me to clamp it in place using the same holes that will be used to install it when finished. Anyone here with knowhow on polycarbonate? If this route gets too costly or complicated the lexan may be replaced with teak and the companionway doors may recieve the windows.
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Old 07-02-2007, 06:07   #2
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Lexan is considerably more flexible than plexi, but without seeing your application, it’s hard to say whether you will need to heat form.

I am in the process of replacing 3/8” plexi windows with ¼” Lexan. Some of my windows have considerable curve to them. No problem getting the Lexan to conform to the shape.

See a couple of photos at http://www.stateham.com/sunspotbaby/deadlights/.

In another thread on this forum someone has posted a brief description of the process of heat forming. A quick search should find that info for you.

George
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Old 07-02-2007, 06:12   #3
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Thermo-forming Lexan isn't easy.
To bend lexan (
polycarbonate
) and plexiglass (acrylic polyacrylate) your piece should be clamped firmly to a strong, stable surface, preferably indoors. Some recommend pre-heating in an oven, to reduce “torch time”.
Once you have clamped the piece begin to heat the panel, with a propane torch or high-capacity heat gun, along the line where you intend to have it bend. DON'T put the heater too close for too long, as this will cause the plastics to get cloudy, or even bubble up.
You'll know when the plastic is ready to bend, simply by applying pressure to the free end of your work piece.
Large pieces will require the help of a partner who can apply even pressure along the entire length of the bend, while you heat the plastic, keeping a uniform and consistent source of heat applied until you have achieved the desired bend. Thicker pieces require heating on both sides.
Lexan does not exhibit a sharp melting point, but softens gradually over a wide temperature range - beginning at about 300 degrees F (150 C), to melting at about 420 degrees F (215 C).



In addition to thermo-forming, most plastics can be cold bent (minimum bending radius must be 150 times the thickness of the sheet), without negatively affecting the integrity of the material. Materials 3/16” thick or less are typically easier to bend.

See also:

HOW TO HAVE SEXY WINDOWS!?

Techniques to rebed dead lights (windows)
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Old 07-02-2007, 07:04   #4
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It's probably Lexan as 20 years ago it's about you would have been able to get. Plexiglass wouldn't look as good after 20 years. You don't want plexiglass it is too weak. I doubt you could buy plexi 5/8 inch thick.

Our current boat has doors and our last boat had doors. Once you come to the actual price of the 5/8 lexan you might want to consider custom doors.

Our last boat we had detachable doors with screens / lexan inserts. Not very secure but it had hatch boards too. On a trip you will use the doors a lot and it's only when you are away or need to be secure on a passage that you'll ever use hatch boards.

Current boat has a set of interior doors that recess with screens and exterior doors that are solid and secure with a lock and interior bolt. A good set of doors is a worthwhile upgrade. The big lexan hatch is just something you have to store and try not to get it all scratched up. If your current hatch really has no cracks then the crazing is just cosmetic. You can buff out some of the small nicks if you work through about 3 levels of grit with a bufing wheel.
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Old 07-02-2007, 10:52   #5
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I beg to differ. AFAIK, Plexiglass has been around much longer than Lexan. Lexan is stronger than Plexiglass but Plexiglass is more than strong enough in most applications. The biggest problem with Lexan is it is more prone to UV damage usually seen as crazing. Lexan also has less surface hardness than Plexiglass so tends to scratch and disfigure easier. Plexiglass will usually cosmetically outlast Lexan. Was just on a boat with Plexiglass windows in their hard dodger. After 10 years, 3 of them in Mexico and the rest in SF Bay, the plexiglass looked great. Haven't seen Lexan hold up that well.

In most instances, there is no need and reasons not to take the economic hit of going with Lexan over Plexiglass.

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Old 07-02-2007, 11:45   #6
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I learn't a little about the life of Lexan from a totally different off topic thing I am involved with. The first thing I discovered was how short the life span of Lexan was in sunlight. The lexan loses it's strenght when exposed to UV in a very short time. It is only a coulple of years and the two materials reach about the same strength.
As Peter has also described, Lexan scratches very easily. Plexi is much harder wearing and it take many years for it to deteriorate in the sun.
There are important aspects for working with both that must be done, or you will have a lovely looking panel that simply cracks in a week or two. That is the area of drilling holes.
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Old 07-02-2007, 11:53   #7
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Peter, I would agree on a dodger wind screen. If it broke no water is going to leak any place. For a hatch or for something as large as a hatchboard I sure wouldn't trust it. A wave crashing on a hatch would be more than plexi would take. If you have to put screw holes in it I would never trust Plexi either.

I was replacing a cover for a large dorade box and needed a piece of 1/2 inch material and found a polycarbonate called Markolon. I found it much nicer to work with than Lexan. Lexan will chip and crack if you skip a drill bit on it. You have to be very careful installing latches or screw holes into it.
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Old 07-02-2007, 13:16   #8
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Lexan drills and bends easier than Plexi. FWIW, canopies on jet fighters are Laxan. They withstand bird strikes and spend a lot of time in high UV but last pretty well.

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Old 07-02-2007, 14:47   #9
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The deck hatches ( 5 in total) on my boat are all 3/8" plexi set on wooden frames - she was built in 1975 and these are original - Still strong and not many scratches but they have interior crazing so I'll be replacing them with new plexi - not lexan because I have used lexan on other boats in the past and they scratch easily and cloud over time. Hope this helps.

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Old 07-02-2007, 18:39   #10
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Paul-
IIRC Beneteau made big new 20-odd years ago by using huge slabs of light green tinted Lexan instead of plexi, but plexi ruled--as it does now. When something is 5/8" thick, plexi is already bulletproof and usually cheaper and more scratch-resistant, so I'd guess he's got plexi.

Stuffinbox-
There are dozens, literally dozens, of grades of plexi and Lexan and similar materials from other sources. They vary greatly in PRICE, along with resistance to scratching and UV (which causes crazing) and strength. So, before you spend the money on that slab (I'd be surprised if it was under $200 for the cheap stuff) ask your plastic supplier what materials they stock and what the characteristics are. The really good stuff--UV and scratch resistant--is for outdoor and architectural use and it won't be stocked at the same places that sell tabletops and towel rods.<G> Most palces will charge you for a full 4x8 sheet, regardless of how much they sell you, and then neatly pocket the rest of the slab. So if you're buying a whole slab--make sure you get it and make good use of it. The rest could be turned into companionway boards, storm ports...all sorts of things.

On forming it...ask the folks you buy it from. Many of them already have all the right equipment for fabrication, and a simple bend won't be an expensive job. Better for them to risk ruining that expensive slab, than for you to kludge around with it without production equipment. No?
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Old 08-02-2007, 04:05   #11
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Just replaced my 2 front windows with lexan. It's a Lagoon cat and the panel are about 1 meter by 2 meters with a significant bow.

$160 NZD (about $110 USD) each...including the forming and drilling. Take the old one to a plastic shop and they will bend a new one over the top of it.
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Old 08-02-2007, 08:29   #12
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I want to thank you all for the input, This board is more real help than all the others combined. I think that from a material cost stand point and taking into consideration the thickness of the material the plexiglass will work for the application. That being said 3/8" Lexan is more that strong enough and may conform to the curve without heat. I was going to bed the panel with silicon because of the compatibility with polycarbonate, any opinions on alternate bedding? While I'm on the subject I have heard that Bomar sells a kit with then lens and sealant for their cast aluminum hatches, anyone purchaced one? I am on a roll and if the companionway works out I may attempt to fab the rest myself.
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Old 08-02-2007, 09:29   #13
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Sikaflex 295 UV as bedding compound and sealant. Get on the Sika web site. They have a ton of data on how to properly install. Great stuff. Read the Sexy Window and Rebedding Deadlights threads for more info on this.

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Old 10-02-2007, 00:45   #14
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Bending plexiglas or lexan without heat forming will cause crazing to occur. Not right away but after a year or two. Same with cleaning with petroleum products. Very slight bends are okay. A little bit of stress will cause crazing. Ask a plastic's guy.
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Old 11-02-2007, 20:10   #15
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I personally have had good result's with Shinkolite as an alternative to Lexan.
MITSUBISHI RAYON -SHINKOLITE-

Cheaper and darker tint than Lexan, and was used on a 190 plus foot gin palace called "The Other Woman" in Brisbane ,now called "Islander" so figured it was good enough for me.

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