Bending plexiglass - How to ?

Milacron · Jul 26, 2011

Example.. 3/8" thick clear plexiglass, 2 x 3 feet. If I wanted to bend the 2 foot to a gentle curve, say equal to 3 foot radius.. how would I do that ? Precision is not critical as it would be for a guard that is stand alone...i.e. hinged at the 3 foot length and not attached to anything (other than the hinge). But quality of bend would need to be such that one could see thru it with minimal distortion.

I'm guessing to really do it right one would need to make a hollow round form from metal with heating elements inside. Or maybe just a 1/4 round metal form and move a torch back and forth behind it ??

Alternatively, know of any companies that do this sort of thing all the time I could just send dimensions and order it ?

Heavey Metal · Jul 26, 2011

When we bend race car spoilers we bolt a 1/2'' pipe on the brake and bend just like metal.

tdmidget · Jul 26, 2011

No heat involved? :confused:

CougarMountain · Jul 26, 2011

Generally yes, it does take heat and a form, or jig for best results. Leave the part long for the forming process, as the ends will be distorted otherwise. Trim to length after forming. Also,a scrap piece at each end will keep the ends from getting overheated.

Plexiglass aka acrylic, forms easy. Polycarb is a tougher animal, as it is hydroscopic, and absorbs moisture when stored. Not normally a problem, until it is heated for the forming process, then it gets small bubbles or blisters from the moisture trying to offgas. The best way to prep for forming, is to leave in a vacuum chamber (first choice), or small oven overnight. The down side of an oven, is it can make the protective paper cover almost impossible to remove. The down side to removing the covering first, is the possibility of scratches. BTW, you do want to remove the covering at the bend zone prior to heating. (but you already knew that)

Ries · Jul 26, 2011

One smooth big radius arc would require a pizza oven- but with precise temperature control.
The whole piece needs to be at exactly the right heat.
Too hot, it gets gooey and runs. Too cold, it cracks.

You can buy strip heaters, and make a series of bends, but that wont look as nice.
3/8" is thick stuff, and a strip heater may not even work on something that thick- I have had success with 1/8" and 3/16", using a strip heater and then bending in a brake, so I can set a stop and get repeated bends the exact same degree of bend.

But the best way would be to build a form, heat the entire piece in an oven, then drape over the form.
Torch is not a good idea. Heat gun, maybe, for 1/8", but it wont work on 3/8".

Like many other things, this is something that is easy if you have the right tools and lots of experience, but has a steep learning curve for beginners. (IE, buy a few extra blanks...)

Insert · Jul 26, 2011

When I made a Lexan windshield for the race car, I just painted the original windshield black, set it out in the sun on a hot day. Laid the new Lexan on top, after a while once it was warm, put some small weights on it, to persuade it to bend. Once it was touching the black glass windshield put some heavier weights. As the day cools, it will gradually cool and hold its shape.

With a 3ft radius you might want to do it over a few days gradually.

USMCPOP · Jul 26, 2011

Plexiglas forming manual: http://www.atoglas.com/literature/pdf/135.pdf

robmc · Jul 26, 2011

I made a small windshield for my center console. It needed two 90 degree bends. I picked out the color and the shop bent it for me. Then you can saw it to whatever shape you want. I don't know if this is "sop" at most places.

specfab · Jul 26, 2011

Cougar and Ries have it pretty much described. Drape-forming is really the way to do it. The typical treatment back in the day would be to line the mold where the material contacts with felt, but you will end up with a very slightly textured surface. This does sound like a situation where you need to heat the entire part and drape-form, or you could look for your nearest plastic fabricator and get a line on contracting it.

Pattnmaker · Jul 26, 2011

You could make a bending form out of wood. I have made lots of wooden vaccum tools for customers.

I have not bent acrylic in about 30 years but I would think you could bend it with two guys with heat guns and patience. Make a wooden form, fasten one edge down and let the weight of the plastic start the bend. I would leave extra material on the end to help your bending getting the last bit bent might be hard just like bending steel, better to cut a little of the edge when your done.

It might be easier to make your wooden form and take it to a vaccum forming place.

machfab · Jul 26, 2011

Bending/Forming Lexan

Give Plastic Products in Bessemer City,NC. a call, they form and machine and fabricate all types of polymer. I use them frequently. 800-752-7770

Heavey Metal · Jul 26, 2011

Cool chart , I was wrong you have to go down to .177 to cold bend a 36'' radius.3/8 will only bend to 62'' radius.

SAG 180 · Jul 26, 2011

Plastic for aircraft canopies are heated in a temp controlled oil bath to get the heating uniform enough across the plastic sheet for blow moulding.

CBlair · Jul 26, 2011

Don,

You probably wont have a lot of luck with a propane torch on material that thick. I used to bend thinner material that way and sometimes I would get it too hot and it would get cloudy and bubbles in it.

I believe if you go to TAP plastics they have a online video of using a hot wire heater to gently bend the material. You would have to do it in segments but it wouldnt take that long and should look nice.

Charles

USMCPOP · Jul 26, 2011

Make a hardboard form. Find someone with a powdercoating oven or a good-old-boy with an oil tank BBQ who can heat the sheet evenly to about 310 degrees. Pull it out and slap it down on the form in about 1 minute or less.

KMoffett · Jul 26, 2011

Milacron said:
...as it would be for a guard that is stand alone...i.e. hinged at the 3 foot length and not attached to anything (other than the hinge). ...

If it's for a guard to protect from flying things, Plexiglas (acrylic) may not be the best choice...it shatters. Polycarbonate is more resilient, and is preferred for machine guards.

Ken

Milacron · Jul 26, 2011

KMoffett said:
If it's for a guard to protect from flying things, Plexiglas (acrylic) may not be the best choice...

It's not, it's to keep wayward hands out of the shuttle feed (automatic cold saw)

USMCPOP · Jul 26, 2011

Milacron said:
It's not, it's to keep wayward hands out of the shuttle feed (automatic cold saw)

Then hardware cloth would be easier to deal with.

9100 · Jul 26, 2011

Since no one else has said this, I will put in my 2 cents, corrected for inflation. A group of EAA people made airplane windshields with an oven I made. It was just a plywood box perhaps 6" deep and the size of the plastic sheet, about 4 X 6 feet as I remember from 40+ years ago. The heating elements were electric iron replacement elements, I think from Marcone, mounted on ceramic standoffs. Elements were connected in series to keep the temperature down. We just clipped the Plex on the type of clips you use to hold a stack of documents together and the door was another piece of plywood fitted into the box and held in place with nails stuck in holes drilled from the side. The box was stood on edge so the Plex hung straight down. We left the Plex in the heat until it got good and limber, then a row of people wearing gloves picked it off the clips and wrapped it around a form. On a Stitts Skycoupe, we just made a windshield from furnace duct steel sheet and stretched cotton fabric over it. Then we formed the Plex right on the plane. When the workers got out of synch and messed it up, we just hung it in the oven again and let plastic memory return it to a straight sheet. We left a lot of extra to trim so the inevitable wrinkles would be outside the final piece. You want to keep the temperature of the heating elements low and let the heat soak in. It may take and hour, but so what?

One fellow used the oven to make a gorgeous free blown bubble canopy. We kept in the EAA hangar and finally a windstorm blew it across the field and into oblivion.

Bill

Admin5 · Jul 26, 2011

USMCPOP said:
Then hardware cloth would be easier to deal with.

Perhaps...if I didn't care if it looked like crap, or wanted to raise hamsters in there.

Milacron

Bending plexiglass - How to ?

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