Forming Plexiglas

[Pearson]

I am interested in learning the ins and outs of forming Plexiglas. I want to put a skylight in my airplane. I want the skylight to have a curve outward of about 2 to 3 inches. I have looked at the You Tube videos, but they are mostly about forming thin polycarbonate such as for landing light lens etc.

Does anyone here have first hand experience about the best way to heat up the plexiglas? Also what is the best material to use as a form? How smooth does the form need to be? Is there something that I should use over the form before I stretch the plexiglas over it, such as a sheet of Tyvec? I am using 3/16" thick material. It will end up being about 34" square with about a 2 to 3 inch bulge, so I am not looking for a whole lot of curve. In an effort to keep the experimentation down to a minimum, I would really prefer to hear from those who have first hand experience verses theorists.

[WLIU]

Hello,

You can build a form out of wood and cover it with flannel. The form can be made of 1/2" thick MDF ribs with thin hardboard glued across the ribs to form the curve.

Read the materials properties for the plastic that you are forming. You want to heat it up to the exact temp that it starts to soften. If you get the plastic too hot so that it is really floppy, the weave of the flannel will transfer to the face of the plastic. For a skylight you only need to form a relatively small curve.

The challenge is finding an oven large enough for your form and the plastic sheet. You want an oven that has a temperature control. Preferably an electric oven.

The plastic sheets that I have formed have fit in the kitchen oven. Not sure what the dimensions of your part are.

Best of luck,

Wes
N78PS

[Pearson]

Yes, finding a way to heat a large piece is the challenge. I have heard that windshield makers place the plastic in a vat of boiling oil. But I don't know what kind of oil they use, and don't know how I would heat up a vat large enough to hold a piece the size I need. The skylight is about 35" square, so I need to heat up a piece a little larger than that. The flannel is a good idea. I will remember that, if I ever figure out a solution to the other obstacles.

[Mike Switzer]

You want an oven that has a temperature control. Preferably an electric oven.

I would do some tests on a small piece first, most household electric ovens do no not hold a steady temperature, they actually turn the element on & off so there is a bit of a temperature delta. I have seen videos of plexiglass being formed, and they use specially built ovens that will hold an exact temperature. It also takes several people to get it out of the oven & on the form quickly enough to form it.

[Mike Switzer]

I have heard that windshield makers place the plastic in a vat of boiling oil. But I don't know what kind of oil they use, and don't know how I would heat up a vat large enough to hold a piece the size I need.

If you go this route, see if you can come up with a used fuel oil tank like what people with oil fired boilers use in the basement, and cut the top off. I'd use a vegetable oil with a smoke point above whatever the temp is you need to heat the plexiglass to. Unfortunately the safest way I can think of to heat the oil would be a steam jacket on the tank, and I really doubt if you have access to a boiler that would get hot enough. Any kind of burner under the tank would be rather unsafe.

[flyingriki]

There is a good U-tube video on this by an EAA chapter. Try Google for it.

[Pearson]

There is a good U-tube video on this by an EAA chapter. Try Google for it.

I spent the better part of a day viewing videos on You Tube. I did see one made at an EAA Chapter, but it droned on for three different videos before I realized they were just making nav light covers for wing tips. The challenge with what I want to do is the size of the piece of plexiglass. Thanks for the ideas though. Keep them comming. Eventually someone who has done this before will notice this thread and chime in here.

[WLIU]

It might help if you posted how large the part that you have to form is.

It is not that hard really. Plan on throwing away your first try, but you will likely get an acceptable part on the second try.

I would not resort to hot oil. Hot air us good enough. I did the skylights for a Globe Swift in the kitchen oven. You might consider building an insulated box on the front of your kitchen oven to extend its size. Use the oven temp control to creep up on the right temp. Patience is important.

Best of luck,

Wes

[Mike Switzer]

I would not resort to hot oil. Hot air us good enough.

I tend to agree - I'm having visions of a gigantic turkey fryer fire.

[flyingriki]

A fellow in Kitplanes, a few months ago, made bowed side windows for his plane in his wifes' oven. He built an extension to the oven box with simple materials and was pleased with the results. Probably had the temp info you require. Sounds similar to the suggestion above for Swift Skylights. Good luck!
Link attached.