Teardrops n Tiny Travel Trailers

Hi All

I am in the market for some advice, mostly has anyone experience with hot forming Polycarbonate sheet or Acrylic Perspex.

I have read the data sheets and manufacturing hand books.
I know that its important to dry out these materials before raising the temp forming temp.
I know you should hang Perspex in your oven, but lord knows how.
I know you can Drape Polycarbonate over a former in your oven, but how do you make a male form to stand 150C 330F

I have been pushed toward Polycarbonate because of its impact strength, lower bend temp and the difficulty of cutting perspex.

Basically come clean and tell me how you messed up and I will endeavour not to repeat your mistakes.

Clive.

If you do 060 or thinner lexan (polycarb), you should be able to make those bends with out forming. With the impact resistance of lexan, you wont need a great deal of thickness. Be careful forming lexan. It is hydroscopic. Moisture in the lexan will form bubbles when heated to form. The sheets need to be dried out in an oven before forming.

You can heat form acrylic over wooden forms. Wood is fine at <400F. Be careful to finish the surface very smooth, any texture will imprint on the plex.

Be aware that polycarbonate, while very impact resistant, is not at all scratch resistant, and not very UV resistant. It becomes brittle under extended UV exposure. That's why bullet proof glass windows have to be replaced annually.

<Chas>

Here's the disclaimer - I have no experience with bending plastics - but sometime ago I looked into this for a project I was considering building.

I found DIY articles where people used hand-held heat guns to bend plastics for motorcycle wind screens, lightweight replacement windows for auto racing, etc. Many use a wood buck often lined with 100% cotton cloth (with tight weave) as a form.

With your windows being large, I would consider using an oversize piece of plastic, clamping one side to the buck or form, and then have the free end weighted so gravity could assist you with the bend.

The articles showed two methods of using the heat gun. Some just moved the heat gun back and forth over the plastic, perpendicular to the bend. A few used a "heat box" instead of moving the heat gun. The box is made out of plywood that is 6-8 inches wide with a width slightly greater than the width of the plastic being bent. The heat gun is placed in one end.

For either method, they progressively bent the plastic, starting first at the end closest to the form. As the bend started they moved farther away from the fixed side.

After the piece is bent, then cut it to fit the opening.

I agree with Friz, just go with Lexan. It'll bend and no worries about catching a rock.

I built an airplane and used Lexan for my windshield. Never noticed any degradation from the sun but it was usually hangared when it wasn't airborne.

T

Hi Tony / aggie79 / GuitarPhotog / friz

Thanks for that.

I have put a considerable time in reading and talking, however after a while your mind is swimming, hence asking if anyone had actually done it.

I have been advised that 0.12" (3mm) would be OK and as you say 0.060" (1.5mm) would bend no problem but I an more than a little scared.
I can only sensibly buy Polycarbonate by the sheet but at £170 each ($200) you don't want to buy the wrong one. Cut to order works out to be more expensive for less material. With a full sheet I may get more than one go. Also I want a tint which is making it even more complex.

My own view is to heat forming over cold forming - I want to bond it in place so I think I need a near match to start with would be advisable. If I was going to screw or clamp it in place no question.
I am considering the hot box, drape over a molding route. More complex but a better outcome maybe.
The hot box would also help the drying process. One source advised 70C (170F) for 12hrs.

I am going to make the window frames this weekend and a few more jobs will take me up to my holiday so bending will not take place until week 3 Aug, but I promise to post the disaster no no I mean great result then.

If you have any other lessons please let me know.

Clive

Hi, its been a while since the posts, so you may not see this, but if you do: Did you go with the polycarbonate, and how did it turn out?

Hi

It's a long story which works out in the end.


See
http://tnttt.com/viewtopic.php?f=50&t=63510

And

http://tnttt.com/viewtopic.php?f=21&t=69323

And

http://tnttt.com/viewtopic.php?f=2&t=69 ... 0#p1224150