Bending Plexiglass

Old Goat · by **Old Goat** » Sat Jan 03, 2015 2:07 am

As I posted in another thread, I have a Wurlitzer 2150 that is missing the dome glass. Given the cost of the glass to purchase and ship and my inability to source one more reasonably, I'm thinking about going the plexiglass route. (When I bought the jukebox, it had a 1/8" piece of plexi is in it). I believe the proper thickness is 3/16". Now the 'dome' on the 2150 is extremely simple, just a slight curve from front to back. There aren't multiple bends or compound curves. The plexi may well be able to bend enough to fit in the frame without bending; however, I'd like to get some bend in it if for no other reason than to limit the force on the aluminum frame. I know you can bend plexi at relatively low temperatures, achievable with a heat gun and/or torch. Has anyone tried to do this? If so, what type of plexiglass did you use, did you cutout cauls for the curve, how did you heat it, did you heat in one area and slowly work down the glass? If you haven't done this but have some thoughts, I'm always glad to hear them and take under advisement.
Thanks
Brooks

DoghouseRiley · by **DoghouseRiley** » Sat Jan 03, 2015 3:14 am

Here's my two penn'oth.

I think you'd have to be very careful, as ideally you need to heat the whole surface at the same time. I've bent plastic curtain rail successfully with a hot air gun, but if you apply too much heat in one place you can ruin it and there's "no way back."

Why not make a former out of plywood constructed to near enough the correct curve and then place the plexiglass on it and place weights on the ends and leave it in a warm room or cupboard for a few days and see what happens? You could try increasing the weight over a few days. You wouldn't have to get it exactly right, I'd think, near enough would do.

I had a few sheets of perspex from a recycled suspended ceiling stored in my garage, one of which had some stuff piled on top of it for a few years had bent a bit as there was a piece of 3" X 2" under one edge. The garage would have suffered some extremes of temperature in that time but I've no idea how long it took it to bend.

But maybe someone who has done it might have a better idea.

eddie · by **eddie** » Sat Jan 03, 2015 4:11 am

I have some experience in this. It isn't as easy as it seems, but it is possible. 1/8" isn't too bad, but thicker is tougher. Different plastics have different forming temperatures. Lexan (polycarbonate) forms at around 350f. You need a form. Can be wood. You need an oven big enough and has a means of circulation to avoid hot spots. You have to "dry" the plastic before you bring it up to forming temp. Sounds crazy, but if you don't you will make a mess. Bubbles everywhere. To dry, you bring it up to a temp under the forming temp...say 250 for polycarbonate, and hold it there for several (many) hours. Amount of time depends on the material and the thickness. 1/4" polycarbonate will require 15-25 hours of drying time. At the end of the drying period, you raise temp up to forming temp. The plastic is easily molded at this temp, but cools quickly. You have your form ready, covered with felt. Quickly take it out of the oven and lay it on the form and it will drape. Done. let it cool. Like I said...sounds easy. Hope this helps. There are companies that will bend glass for you to your specs. Not cheap, but messing up 5 pieces of 2'x3' pieces of 1/4" polycarbonate isn't either.

Old Goat · by **Old Goat** » Sat Jan 03, 2015 7:17 pm

Given that I don't have an oven large enough to hold the piece, the cook it in the oven plan won't work. I have viewed several Youtubes with people bending plexi with a homemade tool made with a hairdryer, so I'm leaning towards the approach alluded to by Eddie. That is, build a form, clamp it in and apply heat. That having been said, I may also try to contact local fabricators to see if they do this kind of thing.
Other ideas?

eddie · by **eddie** » Tue Jan 06, 2015 9:19 pm

You can give it a shot, but I don't think you will like the result. A heat gun is too localized. you get one spot hot enough to bend, another spot has cooled. For it to look decent, the bend has to be very uniform. Almost optically perfect.

kentmoore · by **kentmoore** » Tue Jan 06, 2015 11:32 pm

After about 6 months of cleaning it you won't be happy with the looks anyway. Go with glass.