Bending Perspex, Need Help!

[Robert Lambie]

quote :

i don’t now the full in’s and outs, i’ve always used a (don’t know what it’s called) but it’s eight feet long!! and bends all my pvc perfect!!

what are you talking about nik? 😆 😆 😆 😆 😆
i wanna know now too 😉

just joking but i use a heat gun etc.. 7 it works ok for us.. just thought you have a hidden secret method 😉 😀

on a diff note, i have heard like you say nik, heating wires bit for perspex etc. do you know how thi is achieved.. 🙄

[Nicola McIntosh]

your asking a bit tonight rob!! 😀

sorry i will post something more readable in the morning!! machine i have and the (hot wires as it’s called) tomorrow!! 😛 😛

Nik

[Richard]

Googling for “acrylic line bending” turned up this which seems to cover most aspects.

The main point is that if you require a constant radius bend across the width of the material, you must be able to heat only the bit that forms the bend, across the entire width, and the full thickness of the sheet to the correct temperature.

If you don’t get the full thickness of the sheet to the correct temperature, the cooler edge has to stretch causing thinning of the bend which looks very unpleasant.

It has it’s problems, but it really does work a lot better with the right equipment… unfortunately, I don’t seem to be able to find any links to suppliers.

I think it’s time for bed now (sleep)

[Rodney Gold]

Doing a one off bend isnt worth making a bender for , however a heat gun and some supawood or asbestos will do.
A heat gun apply too much heat , Im talking about the fact it warms up too much area and its difficult to maintain a good bend
So you use 2 pieces of supawood or asbestos to only allow a narrow strip where you are bending to be exposed and heat it there , this will get you a nice sharp bend and you wont see wavers and distortions etc , the slit exposed should be about 1/3rd to 1/2 inch wide. The problem with a heat gun is that waving it around cant get you an even heat distribution so you should traverse the slit and overshoot a bit on either end and do it slowly and evenly.
If you see bubbling at the bend , the temp was too hot , perspex becomes elastic at 180 degrees or so. You have to hold it in position till it cools or make a jig. Perspex is VERY stressed this way and often starts developing stress cracks at the bend , especially extruded perspex. NEVER clean the perspex or bend with spirits or the like , guaranteed to stress crack.
A wire bender is the best , basically a thermostatically controlled resistance wire (same as used in heaters) that is in a slit of asbestos or some other heat insulating material where the width of the slit can be varied to change the heated area. You can do the same with solid strip elements rather than wire (straight elements like those in an oven)
However wire is so thin and the heated area is so localisesd that a wire bender allows EXTREMELY sharp bends over a wider element type heat source. Commercial benders have better heat control and fancy clamps and built in angle plates etc to allow precision bends , but home builts get the same job done.
The secret is the temp control , it has to be pretty spot on for the best bend.
The thicker the pex , the more critical it is to be heated throughout and its often a good idea to turn the piece over and heat the other side of the bend too as well as having a wider slit to heat more area. Ideally notches should be cut either end of the bend to stop the ends “bulging” (but unless you have laser cut or CnC routed the panel , it might be a difficult thing to do)
Pex is an amazing product , if you havent overheated the bend and had the pex start breaking down (burning it or bubbling) you can heat it agian and it goes back to shape , pex doesnt melt , it gets rubbery. We have press formed pex (3d letters) and then reheated the press formed sheet and it goes back to flat. Once you bend pex and see how easy it is (especially with a bender) , you can make some wonderful things.
Hope this helps.

[Nicola McIntosh]

rob as promised from last nights post!! 😀

the bender i use is a Terra Therma 8′ bought in leighton buzzard 😛
it has heat at the top and bottom which disperses through a tiny space(like a long slit) you put the material in and pull down the lever and time what ever material you use!! take it out and bend!! 😀 😀 i was going to take a picture but it’s too big to fit camera!!

the hot wire thing, was when ed was in london, he cryed into a signmakers in bricklane, what the guy used was an element out of a electric fire stretched out to a long wire, sitting on a bed of asbestos!! he said it worked a treat!!

Nik