Bending Polycarbonate

[RDavidson 183]

I thought I would start another thread for bending polycarbonate...

I watched some youtube videos on bending plexi, most guys were using a heat gun. So I pulled the heat gun out and put a piece of plexi (.125) in my break. I started with a strip 2" wide and about 2' long. It was surprisingly easy to bend once warmed up. I had to keep the heat gun moving back and forth to avoid getting the plastic too hot and distorting it. It would bend almost a perfect 90 degrees with a very small turn radius, but looked best when given about 3/16" to make the bend.

I also figured out that I could leave the protective plastic sheets on both sides of the plexi and they did not melt into the surface and prevented the break from leaving marks on the plexi.

Next I tried a bigger piece, 1 foot by 1 foot. I tried to bend it right down the middle. It wouldn't do it! I guess polycarbonate can release heat in a hurry? I couldn't get enough heat spread evenly to make it bend.

I'm taking my cut pieces to the plexi expert tomorrow, and I'll let you know how he does it! I didn't want to risk screwing up this Plastic Gold $$$$$!!!

I read that one guy used a heating element from an old heater, stretched it out in a straight line.

Anyway, I'll let you know.

Ron

bottom bend (bending left) was done with basically no bend radius, top bend I used about 3/16" of space for the bend radius.

[TJay 1041]

Here is how I did the Fisher.  I bent the edge around the corner with a heat gun and a steel roller, worked really good, I'm excited to do the Kitfox.

[KFfan 151]

TJay

 

You didn't have any problem with the steel sucking up the heat or did you heat the roller as well?

Nice looking result!

[birddog486 21]

Ron,

 

You probably know this but for others that dont, Polycarbonate is Lexan and Acrylic is Plexiglass. The lexan can be cold bent in a brake where the Plexi requires heat to bend in a tight radius or it would just snap. I used the Makrolon Lexan with a little heat on it to make the tight windshield bend at the edges. It's a real trick getting consistent heat at about 250 on the whole area for a smooth large radius bend that will hold it's shape.

 

Travis

[dholly 718]

If you review the polycarbonate manufacturers recommendations for heat bending, you'll find most say to apply even heat to the sheet well beyond the bend line for the best results. When doing my last poly windshield/skylight replacement, I set up two halogen work lights in the cabin below the sheet and just let it warm for several minutes. Made the job much easier and the tight bend radius for the front spar carry through went off without a hitch as I cleco'd along. I've tried a heat gun to apply localized heat on that radius area only in the past with mixed results so I believe the 'sheet heat' recommendation removes a lot of stress. I am convinced you could more evenly heat a piece of poly large enough for a 1-pc turtledeck using work lights underneath which might make the job easier. Those suckers can get pretty damn hot! I planned on trying this for my A+.

[EDMO 1078]

We cold-bent Lexan to 90 degrees in Aviation school - probably about 1/4" radius, took a lot of pressure.

I used a heat gun to bend some for my boat windsheilds, and got some small bubbles in one bends - guess it was too hot? Didn't ruin it tho.

I was told that after Lexan is heated, that it will crack like Plexi if you try to cold-bend - I cant verify this as I have never tried that.

EDMO

[RDavidson 183]

@TJay that looks great! Good idea using the roller.

@Travis, thanks I was using those interchangeably and they really aren't

@ Doug, that is a great idea using shop lights! They do get really hot and pretty evenly.

@ Ed, I was told that if you cold bend polycarbonate it causes small fractures that eventually will turn into large cracks after heated and cooled in the weather. He told me that, after looking at my 20 year old polycarbonate cold bent doors that didn't have one crack showing, so take that with a grain of salt! I think it is all a bunch of whooeee! Bend it...as long as you don't crack it or break it, whatever works for you. It's not like these are critical structures in our planes! As long as I don't have a crack going right through my line of site, I'll call it good...

Ron

[EDMO 1078]

My buddy called me this morning asking about sealer for Lexan - All I could tell him was that Spruce or Wicks has a "sealer for plexiglass", and RTV#732 in clear, white or Black, for sale. I don't know what sealers are safe to use with Lexan, but have heard that you should not use certain ones. Maybe not the ones that smell like vinegar?

Anyone have info on this?

EDMO

Edited 25 Mar 2015 by Ed In Missouri

[dholly 718]

Lots of good info can be found on product manufacturer's websites. For example, check out the Technical Resources FAQ's at Curbell Plastics: http://www.curbellplastics.com/technical-resources/literature-technical-documents.html

[KFfan 151]

Thanks!

Looks like some great information.

[EDMO 1078]

Thanks Doug,

Some good info on that site about removing paper too.

EDMO

[1avidflyer 1983]

Where did you see the paper removing tips Ed? Jim Chuk

[EDMO 1078]

Jim,

I think it was page or chapter 19 and on down from there???

There is also a section about cleaning, removing scratches.

EDMO

Edited 26 Mar 2015 by Ed In Missouri

[Geoffrey Thorpe 31]

We cold-bent Lexan to 90 degrees in Aviation school - probably about 1/4" radius, took a lot of pressure.

I used a heat gun to bend some for my boat windsheilds, and got some small bubbles in one bends - guess it was too hot? Didn't ruin it tho.

EDMO

Polycarbonate (Lexan) will absorb a little water over time wich will boil and make bubbles when you get it hot enough to bend. The solution is to pre-bake the polycarbonate for a while at 180 F or so or to use fresh stuff.

[dholly 718]

I've taken the liberty of cherry-picking a few documents from the Curbell Plastics Technical FAQ I linked earlier:

- Polycarbonate (Lexan) sheet:

Here is the MAKROLON brand Polycarbonate (Lexan) sheet Fabrication Guide: http://www.curbellplastics.com/technical-resources/pdf/polycarbonate-fab-guide-makrolon.pdf

Here is the PLASKOLITE MUSTANG brand (Copolyester) sheet Fabrication Guide: http://www.curbellplastics.com/technical-resources/pdf/copolyester-mustang-fabrication-guide-curbell.pdf#search="Polycarbonate%20sheet"

- Acrylic (Plexiglass) sheet:

Here is the OPTIX brand Acrylic (Plexiglass) sheet General Guide: http://www.curbellplastics.com/technical-resources/pdf/acrylic-fab-guide-optix.pdf

Here is the ACRYLITE brand Acrylic (Plexiglass) sheet Cutting Guide: http://www.curbellplastics.com/technical-resources/pdf/acrylite-cutting-guide-curbell.pdf

Here is the ACRYLITE brand Acrylic (Plexiglass) sheet Working Guide: http://www.curbellplastics.com/technical-resources/pdf/acrylite-working-guide.pdf

Here is the ACRYLITE brand Acrylic (Plexiglass) sheet Fabrication Guide: http://www.curbellplastics.com/technical-resources/pdf/acrylite-fabrication-guide.pdf

Here is the PLEXIGLAS brand Acrylic (Plexiglass) sheet Fabrication Manual: http://www.curbellplastics.com/technical-resources/pdf/acrylic-fab-guide-plexiglas.pdf

Here is the PLEXIGLAS brand Acrylic (Plexiglass) sheet Forming Manual: http://www.curbellplastics.com/technical-resources/pdf/acrylic-forming-plexiglas.pdf

[LSaupe 123]

Thought I would jump in here.  Just pulled off the paper on my Model III windhsield and find the wing root corners have crazying about 4" long.  Other than cosmetic is this a real concern (i.e. cannot be flown as is).  It is 0.100" thick acrylic.

 

If a replacement is required, any pro's and cons on Lexan vice Acrylic?  Sounds like preheating might be the way to go to prevent future crazing?

[EDMO 1078]

It could have been stored badly during its long rest - How much over 20 years has it been since a Kitfox 3 kit was made?

Buy .090 Lexan, and use the old WS as a pattern.

EDMO

Edited 28 Apr 2015 by Ed In Missouri

[RDavidson 183]

LSaupe,

The basic differences are...

Polycarbonate (Lexan) 200x stronger than glass, but easy to scratch

Acrylic 4 to 8x stronger than glass, more scratch resistant than Lexan and I think easier to heat mold.

My Starduster Too windscreens are Acrylic and it is amazing the wind force they take, so in the big scheme of things, the strength is not a big issue in respect to wind force. However, Acrylic will crack in a heartbeat if you use the wrong type drill bit, also if you are using an aggressive saw blade or if you put it under force like an over tightened machine screw.

I just cut a bunch of 1/8" polycarbonate and you can cut it with just about anything...I used a Dremel circular saw for long straight cuts, jig saw for small curvy cuts, and bandsaw on small pieces all without cracking of any kind. You can use normal drill bits too.

On the acrylic windscreen I had to make a drill bit...do this by filing a standard drill bits face to a point, I think 60 degrees is what is suggested. You can also buy acrylic bits. I used a very fine toothed coping saw to cut the acrylic. The Magnum's windscreen is acrylic because it is shaped and formed. I think the other Avids are a sheet with cut outs for your wing root, at least the MKIV I've seen is that way. I don't know about the Kitfox III...

I would use polycarbonate for ease of cutting and drilling, plus you get the strength!

Hope that helps...

Edited 7 May 2015 by Ron

[Ironman Al 35]

Has anyone tried buffing out a wind shield? Factory Kitfox one? Probably Lexan.I've polished out tail light lenses with real good results to major scratches and scuffs, like new, using just regular auto paint polish resin past and a buffer!

[akflyer 1427]

Has anyone tried buffing out a wind shield? Factory Kitfox one? Probably Lexan.I've polished out tail light lenses with real good results to major scratches and scuffs, like new, using just regular auto paint polish resin past and a buffer!

I have done multiple ones using the headlight buffer kit from the local auto parts house.  It comes with the little wheel you use in an electric drill.  About 15 minutes and I can have the windscreen, skylight and doors done with my battery op drill.

 

 

[KFfan 151]

I've done my headlight covers by hand with 600 wet paper followed by 1200 wet paper. They look good from the outside. Can't seem to get my head inside to check the view out...

[Ironman Al 35]

Would it be better to take wind shield out first?