For an electronics chassis I need to fabricate a cover with a couple of 90 degree bends, the cover has a cut out to allow viewing of a readout.
I was going to use 1.6mm Aluminium, but if I use clear polycarbonate I won't need the cutout - the label can be used to obscure all other areas. The top surface of the panel would be held with support pillars.
...........so will 1mm or 1.5mm polycarbonate sheet hold a 90 degree bend over a length of 120mm?
Sort of like this:
================================  | | ^^^^^^^^ | |   P |DISPLAY| P   I I   L L   L L  A A R R _______________________________________________________chassis base _______________________________________________________
The usual rule I have seen for cold bending polycarbonate sheet is that the bend radius must be a minimum of 100 times the sheet thickness, about 150 MM (5.9 in) in your case. Is that practical for your application?
If not, you will need to preheat along the bend line. Absent the proper equipment, you may be better off taking your cut sheet to a local shop or artist that works with polycarb sheet.
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Polycarb also has a tendency to bubble if you heat it to bending temps. You have to bake it for a while at a lower temperature to drive out any absorbed moisture before heating to bending temperature. Acrylics don't have that problem.
That rule of thumb is for heavier sheet. Thin sheet can be cold-bent in a brake, though the bend may spring back a bit over time. This shouldn't be a problem if the piece is fastened to the chassis on both sides of the bend. Good fabrication info here...
I built my own strip heater using the 110V. heating element out of a $1 Maytag dishwasher. In the dishwasher, the element forms nearly a full circle with the ends bent down at 90 deg. through the bottom of the tub. After gently straightening the element, I mounted it in the steel box from a single tube fluorescent fixture with one end free to slide in a slot when the element heats up and expands. I have used this for a couple of hours at a time and have not seen a need for any temperature control. The way it is set up, the material being heated is about 1/2" above the element and doesn't take long to reach bending temperature. Works great and the best part is that it is totally built from junk. Oh yeah, the element I used straightens out to something more than
40". (43" I just went down and measured it) I have bent 3/8" Lexan right over double, but the moisture content turns the bend white. All in all, a fun toy. Gerry :-)} London, Canada
Hmm ... may I presume that the ''s at the right hand end of the lines are supposed to line up?
If so, you must have posted using a proportional font, which gets seriously distorted when viewed with a fixed-pitch font -- and somewhat less distorted, but still distorted, when viewed with any other proportional font than the one which you used -- or even the same proportional font on a different machine.
The problem is that each character has its own width in a proportional space font, and thus the width of screen that you thought that you were using actually is not what others see.
Really -- a fixed pitch font (such as "Courier") is the best choice when posting ASCII graphics to usenet. Most any computer which uses proportional space fonts can be switched to use fixed space fonts, but the alternative is not true -- especially for those reading usenet from a stand-alone ASCII terminal.
As an example, I will post a box below, with various characters inside. If you view it with a proportional font the greater the distance from the left-hand edge, the more out of position things will be, but if you view it with *any* fixed pitch font, you should see the same basic shape.
Another good thing to avoid is tabs, because different systems and users may have the tabs set at different places. Below is a line which on my screen lines up with the box sides above, but it is mostly tabs, not spaces.
Now -- as to you your polycarbonate. How sharp a bend do you want to make for that 90 degrees. I think that with a generous radius you can get away with the 90 degrees -- if you bend it slowly. With something like Plexiglas, however, you will need heat to allow the bend to be made.
The actual *length* of the bend line will only matter in terms of how much force you will need. With a reasonable thickness, you can probably do it quite well with a sheet metal brake, or perhaps improvise something to allow you to accomplish the task.
Also -- how *thick* do you want the polycarbonate to be?
A better way to do a strip heater for polycarbonate and other plastics: Use two equally long pieces of at least 10x30mm square aluminium tubbing (make them as long as you need) , laying them on the broad side. Leave a space of at least 4mm between them. Plug the ends and add some pipes onto wich you can connect water hoses, so that water circulates through the aluminium tubes (for cooling purposes). Hang a straight heating element (use your imagination, depending on the lenght you need), right under the gap between the tubes. There are many many ways to make a "chassis" for this device, I've seen it done out of refractary bricks that had a groove carved to fit the nichrome wire - with the aluminium pieces just laid on top of them - and for myself i did a rather complicated stand, that had some sort of reflector behind the heating element (I had no refractary bricks). They all worked great.