new windscreen and hints on heating and bending pls

[Hugh Jardon]

I am expecting my new windscreen in the next day or so and i need to put in some gentle bends. I am told this is relatively simple using a heat gun/paint stripper type gun.

however i am after some hints and tips....dos and donts...so i dont fech it up

can any of you experts give me some guidance before i roll up my sleeves

[Kernow Buoy]

Hugh
not an expert but I've had a play, I found 3mm Lexan to be really easy to bend into shape with a hot air gun even taking on a bend of up to 90 degrees was no problem, I applied heat for no more than a minute or so and away she went, having tried that I bought a sheet of 6mm and found it a real sod in comparison, I thought I took my time over heating it but couldn't get it to bend without getting it really hot and by then I'd managed to burn some air bubbles into it, where I'd applied heat had gone misty as well. I was still trying to get a bend of 90 degrees and although I succeeded it looked crap!
It's still in my garage if you want it.

[Hugh Jardon]

thanks mate for the offer, i think i will practice on the first one i was sent until i master it a bit


question...did you apply the heat gun directly to the material or did you point it away a bit, how hot did you get the stuff

unfortunatley or fortunatley mine will be 6mm plus, so great for strength but interesting to bend i suspect

[Biggles]

I know patience is a virtue and you night need a lot of it to get the conditions I suggest. Might also be a daft idea. Are you going to wait until the sun comes out to play and use some of the ambient temperature so you don't have to apply as much direct heat.

I remember looking in to this a few years ago and it seems High schools and Universities have a some sort of a straight heater that is good for bending the stuff. Do you know any teachers that could help ?

[codprawn]

Originally Posted by Kernow

Hugh
not an expert but I've had a play, I found 3mm Lexan to be really easy to bend into shape with a hot air gun even taking on a bend of up to 90 degrees was no problem, I applied heat for no more than a minute or so and away she went, having tried that I bought a sheet of 6mm and found it a real sod in comparison, I thought I took my time over heating it but couldn't get it to bend without getting it really hot and by then I'd managed to burn some air bubbles into it, where I'd applied heat had gone misty as well. I was still trying to get a bend of 90 degrees and although I succeeded it looked crap!
It's still in my garage if you want it.

Maybe the heat was too localised? Holding it in front of a gas heater or similar may have been better.

I have heated smaller bits in a fan oven so that I could mould/form them - windscreen may be a bit big for that though!!!

[Biggles]

Could you use hot water ?

Maybe a big tub of the stuff. Heat slowly and keep trying to bend. As soon as you have your bend remove the heat.

Just an idea. Might be another stupid one though.

With all these ideas sounds like trying to keep the plastic from frosting is going to be the key.

[Biggles]

Also found a couple of these.


The real way to bend acrylic is with water-cooled heat pipes.
A long heat element is exposed on one side - the top - while all other three sides are hollow steel pipe with water running through it.

here it is in profile.
http://i48.photobucket.com/albums/f2...icheatbend.gif


You set your jig up, lay the sheet acrylic over the top and a line is heated through. then you get a long block of wood or metal with a square edge and bend the acrylic over it, ever-so slightly over bending it. Keep the acrylic in this position after bending it, keeping the squaring jig set up.
The rounding will happen naturally as it is an inherent property of acrylic.
To get more sharper corners, you can score the underside of the sheet with a circular saw or router set up under a bench. This will weaken the acrylic and make it more difficult to bend without snapping or breaking.
The main thing you need is care.

Of course this isn't at all helpful, because you want to do it at home.

Anyway it shouldn't get cracks or discolouring if it is quality acrylic: methyl methacrylate.
You may however get small bubbles forming within the acrylic if it is heated too much too quickly.
If you are going to try it i'd suggest doing it like Rybags has explained above, but make sure that the heat is only applied to a small section of acrylic. You can 'mask' the acrylic with wooden blocks so that only the exposed area will be heated. In addition to this, peel off the masking paper only on the area that you will be heating, on both sides of the acrylic. I suggest using a long metal ruler or straight edge to tear it away.
Maintaining a straight edge - after bending, keep the sheet in the jig until it is cooled. It is very important to maintain the pressure on the bend, on both sides.


Maintaning the bend: acrylic is a thermoplastic which retains it's shape after heating and reforming. Other plastics are less forgiving. Simply make sure that the bend is done right in the first place, and let the acrylic cool of it's own accord. Don't muck with the heating or cooling too much or you will warp it.

here is an image i googled that could help.
http://i48.photobucket.com/albums/f2...crybending.jpg

It's a pretty good way of setting up a bending jig. You could use a smaller diameter round bar, but the acrylic is naturally going to form a small radius even when bent around a square edge. Don't go *too* square though, as it might dent the acrylic.
Like I said you'd want to clamp heavy square-shaped stuff around it after it has been bent in order to maintain it's shape while it cools.




http://www.atomicmpc.com.au/forums.asp?s=2&c=18&t=3864



I lay no claim to any of this. Just wanted to pass the info on.

[Kernow Buoy]

Originally Posted by Hugh Jardon

question...did you apply the heat gun directly to the material or did you point it away a bit, how hot did you get the stuff

On the first bit (3mm) pointed it away and gradually came closer moving along the seam of the intended crease, also applied heat from below, all of a sudden it started to bend so I kept on with the heat, pushed down with my other hand and away it went to a nice clear 90 degree bend.

So brimming with confidence tried the same with the 6mm and basically was too impatient, ended up with the nozzle all but touching the surface and was whacking heat into it far too quickly, managed to melt my rubber glove, burn the table, scorch the lexan and then it bent, if I was to try again I'd have 2 heat guns on it as the 6mm seemed to lose heat as I moved arond it, as I said initially though Hugh I was after a right angled bend, a gentle curve would have been easier.

[Kernow Buoy]

Originally Posted by codprawn

Maybe the heat was too localised? Holding it in front of a gas heater or similar may have been better.

I have heated smaller bits in a fan oven so that I could mould/form them - windscreen may be a bit big for that though!!!

Yes t'was Codders, not sure I could have held it by a heater, the 6mm really was very hot before it gave.

[codprawn]

http://www.ultimatehandyman.co.uk/perspexmanual.pdf

Very useful.