Place your plastic on the heat bender. You will be able to see the plastic distort from the heat build up. This can take anywhere from 10 minutes when your machine is first heating up to 30 seconds when your machine is nice and hot. You should always stay in the room and watch your plastic. If you don't, you could burn it, which will cause it to bubble and turn black, at which point your plastic will be as good as scrap.

You can test your plastic to see if it is malleable. Once it is easy to bend, you have found the right spot. Take it off of the bender and put it into an adjustable angle setter or a pre made mold with the appropriate angle cut into it. For the best results, push your piece into the setter and then clamp it down. You should only have to wait a few minutes until your piece is cool enough to handle!

As a finishing note, you may have noticed that the outside edges ave bowed a bit. feel free to sand them down, they are essentially jump left over squished material.
We made one similar when I was a kid. Made a plywood surface and got some asbestos paper (used as underlayment for siding at the builders supply at the time) and stapled it to the top of the boards with folding it to line the channel, and laying the heat tape in the channel. Hooked the tension loops on the tape on nails or screws at each end and plugged it in. The wood underneath got warm but never near charring, and the heat tape looked like the one TAP sells today. ... Yea, you can't get asbestos paper anymore, but such is progress. ... Oh yes, this was about 55 years ago if I remember working on it with my Dad in the garage. ... <br> <br>We built all kinds of things, wind tunnel, demonstration NMR rig, simple EDM machine (from plans in Popular Science), etc. I even remembering getting a 5lb vial of Mercury and letting my younger brothers play with it on the kitchen table. Eventually we made a barometer out of it. ... <br> <br>All the kinds of things CPS and OSHA and HAZMAT teams would be all over us for these days. ... My sons cub scout leader would be hauled away today for using a 'trick' with brake fluid cleaner to start a fire these days (it generates sarin gas when heated near burning as it's default break down, so never use break cleaner to clean metal before or after welding while it is hot. I have heard from a couple of welders that had a close call and permanent neurological damage by accidentally doing this. Carburetor cleaner is OK, just not brake cleaner.)
so you only need to heat one side the side that stretches not the side that compresses i would have loved to make some perspex speakers but i have to many and the cost of a mistake
I built my own strip heater over 20 years ago, using a flexible heating element I purchased from TAP Plastics in San Jose, California. The support structure was made of 1/2-inch plywood, and the channel in which the heater lies was lined with ceramic fiber board obtained from a local hardware store. The ceramic fiber board was glued to the plywood using silicone caulk. Simple cheap, and works well with acrylic sheet goods.

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