Bending Plexiglass

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tipusnr

tipusnr

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I've been seeing some of the nice pen stands many of you have made and have what might seem a dumb question. How do you bend the plexiglass? I know that it probably involves heating the material but using what and how hot? Are there any physical requirements for the plexiglass (minimum/maximum thickness, lexan rather than simple plexiglass, etc.)

Inquiring minds may not want to know but I do!
 
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Hi,
I bend mine using a simple butane torch. NOT TOO CLOSE !!!! Put the plexi piece on the edge of a table or anything with a sqare angle, let the part that you want to bend over the edge and heat slowly. The part will slowly bend down, do not push on it to help it unless it is a very short edge that wont bent by itself. You could make a grouve into your pexi piece if you push too hard on hot plexi. You can make a wood jig with different angle for different angle bend. The very important part is to not put the heat souce too close. Paint stipper heater could probably work too but i never tried it.

Hope this help


Alfred
 
You can also put it in a conventional or toaster oven for a few minutes. No more than 200 degrees should do it. If you know what shape you want it, cut a template from some scrap wood and simply bend it over the template and let it cool for 30 minutes.
 
OK, dumb question I know, but what if you put it in the microwave.?.
and no I haven't tried it, just wondering if it would explode or melt or bring the wrath of the wife down..??[?]
 
John,

I don't think microwave will work.

Microwave "excites" water molecules to generate the heat. Won't have that in the flexiglass...unless you immerse it in water and let the water boil...even then I am not sure you will easily reach the melting point of flexiglass. [;)]
 
Originally posted by Dario
<br />John,

I don't think microwave will work.

Microwave "excites" water molecules to generate the heat. Won't have that in the flexiglass...unless you immerse it in water and let the water boil...even then I am not sure you will easily reach the melting point of flexiglass. [;)]
Click to expand...

Dario is correct about how the microwave works. That's why your plasticware does not melt in the microwave. However it has been proven that water can be "superheated" in a microwave and be much hotter than the 212 degrees where water boils at sea level. It takes very specific conditions, but id can happen.

http://www.phys.unsw.edu.au/~jw/graphics/superheatingsmall.mov

http://www.phys.unsw.edu.au/~jw/graphics/superheating.mpg

http://www.phys.unsw.edu.au/~jw/superheating.html

I have softened 3/32" plexiglass to the point where it could be bent on a form by boiling it in water on the stove.
 
Scott, can you describe the process you used? When you say that the plexi was soft enough to be "bent on a form", 1) how long did it stay that way, and 2) was it soft enough to be bent by hand (e.g., with pliers, etc.), or would something more significant, like a form, be required?
 
This is how airplane windows and windshields are made. A form, they use plaster. wood will work, the glass is cut bigger than needed by at least an inch, then it is put in an oven at about 200 and never touched until the glass "slumps" over the entire form like very thick molasses, then it is cooled in water and allowed to "cure" the shape for 24 hours (so the "memory" of the glass won't come back. only then is it trimmed to final size. the form must be perfectly smooth as ANY surface imperfection will transfer to the glass.
 
Originally posted by JimGo
<br />Scott, can you describe the process you used? When you say that the plexi was soft enough to be "bent on a form", 1) how long did it stay that way, and 2) was it soft enough to be bent by hand (e.g., with pliers, etc.), or would something more significant, like a form, be required?
Click to expand...

alamocdc hit the nail on the head.

It's only pliable for 15-20 seconds and it can be bent by hand and the use of gloves.
 
My 2 cents

Be very careful. If over heated some plastics will give off toxic fumes (i.e. use the oven when the wife is out of town). Different plastics have different softening points. The difference between soft and melted mass ain't much so experiment with different temperatures. I have used an oven and it works great if you have forms. I have seen heat lamps used like an oven also.I have used heat guns and it is easy to blister the plastic but with a little practice bending a joint is easy. If you can get a torch to work you are a better man then I. I have seen folks polish cut edges with a torch but I can't do it and I tried. MM works great.

Added comment
http://www.plasticsmachining.com/magazine/199811/acrylic.html
Thermoforming
The typical acrylic sheet forming temperature is 290F to 320F, depending on the amount of shaping (stretching) and the forming rate. An excessively fast forming rate will impart high stresses and decrease craze resistance. To minimize stresses, form at a moderate rate; distribute temperature evenly over the surface and thickness of the sheet. Heating time depends on material thickness and heating method. Higher forming temperatures are needed to achieve greater "draw" or increased definition. Excessive temperatures will produce pimples, blisters, shading changes and other damage.

Acrylic sheet shrinks slightly when heated to its thermoforming temperatures. After forming, cool the part to below 140F to 160F. Make sure the interior is cool as well as the surface, and cool uniformly on all sides to prevent stress.

Annealing
All fabrication induces stress in acrylic sheet. Annealing to relieve this stress is recommended to minimize crazing or cracking that can occur. Annealing can also increase bond strength by 50 percent.

Anneal parts in a forced air-circulating oven. Commercial ovens are designed for annealing and heating plastics; restaurant-type ovens also do the job. Heat the acrylic sheet to 180F, just below its deflection temperature and cool slowly. Heat for one hour per millimeter of thickness -- at least two hours total. Cooling time should be a minimum of two hours. For sheet thicknesses above 8mm, cooling time in hours should equal thickness in millimeters divided by four.
 
In fact, the torch is my best way too. The trick is to move it continiously at moderate speed over the piece you want to bend. Staying too long at the same place will give you trouble (DAMHIKT)[:I].
The peice will fold by itself when the plexi got to the good temperature. Let it cool down 10 min and voila. This will work with all the forms and mold you can think of(well almost).

For your info: You can easyly cover an ourside table by simply put a sheet of plexi on it, leave about 3 or 4 inches over each side cut a slot a 45o in the 4 corner and heat it up side by side with a torch until it fold. Then, put the table on one of its side and fold the remaining under the table top. Do that for evey side and voila, a perfectly coverded table and easy to clean. When you start to master this technique, you will start covering everything with plexi.
 
Tipusnr,
Why not make life easy. Use lexan (polycarbonate). You can bend it cold. I put up to 1/4"in a sheet metal brake at work and I can bend it sharp at 90 degrees without breakage. I usually bend it past 90 to take springback into account. In fact polycarbonate is so soft you can take a hand plane and take a curl off it. If you go to the big box store, the replacements they sell for storm doors is almost always lexan. Plexiglas is brittle and can break into shards. Thick lexan is soft enough it will take a bullet and it will stick instead of breaking. My ex-military buddy at work has the sample on his desk for proof.

The best place for a flame around these materials is to polish the edge. I use a bench scraper to take off the saw marks, polish with 600 grit, they rake a cool flame over the edge. It will shine like the face.
 
No need to use a flame to polish the edge when acetone will do nicely...

As far as heat for bending, a hot air gun will do the job, or what the "pros" use is a nichrome wire hooked to a car battery or charger to heat it up..
 
Thanks for all the ideas - both cold and hot. Now all I need is to make time to try 'em.

Oh, and Tom, who are these "pros" and how do I keep them away from my vehicles?[:D][8D][:D]
 
Professionals use a strip heater. I used to have one when I taught wood shop. It would be easy enough to make one if you wanted to mess with it. All it really has is a nichrome wire strip down in groove. You could make one with some metal, a power cord, a light dimmer to control the temp, and some nichrome wire from an old toaster. Lay the plexi with where you want the bend directly over the heat strip, test it until it gets soft enough to bend some, flip it over to equally heat the other side, then grab and quickly bend to the correct angle, hold a few seconds and it's done. Make sure you take off any protective covering on the plexi (saw someone try this with the paper still on it, won't work).

Advantage to this is it creates a straight line to bend while the rest stays flat. The other methods above have their advantages but if you had a lot to make I think making a strip heater is worth the extra effort.
 
I have a strip heater made specifically to bend plexiglass. It's similar to Lynn's, but has a heating element instead of a nichrome wire. The main part is a 12" long straight heating element. Below it is a cylindrically formed piece of sheet metal to reflect all heat upwards. The base, maybe a foot square, is made of masonite with the gap in the middle maybe an inch and a quarter wide that the heating element and reflector sit in. There is a light dimmer on the power cord. The trick for heating is to go slowly and watch when things just first start to sag. Flip the part and heat the same area. Heating too long or at too high a temperature will cause bubbles. When done right, the bend will have a nice 1/2" radius or so and will be very professional looking. It is definitely worth the effort to build one.
 
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