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Re: [TCML] Bending acrylic

To form a simple, straight bend in a sheet of acrylic or polycarbonate, the heat is applied to a very narrow just where the bend is to be formed. Professional bending fixtures use a U-shaped aluminum extrusion with a nichrome heating wire suspended in the center of the "U". The plastic sheet is placed over the extrusion, with the bend line perfectly aligned with the heating wire. After the plastic has been softened, it is slid over to a pivoting bending fixture that creates the desired bend angle and supports the plastic until it cools. The sidewalls of the aluminum extrusion limit the heating of the plastic to a narrow strip.
Now if you want to create a complex three-dimensional shape, the simplest method is to vacuum-form it. The entire sheet of plastic is secured in a large frame, clamped all around the edges. It is heated under a gas-fired or electric radiant heater until the entire sheet is softened, then quickly dropped over a form (either a male "plug" or female "cup") that is an exact reverse of the shape you want to create in the plastic. The edges of the frame holding the plastic sheet are sealed to the surface holding the form, and the air is quickly removed from under the plastic using a large vacuum reservoir tank. Ambient air pressure forces the soft plastic tightly against the form, where it replicates every detail in the form. After a minute or two of cooling, the plastic sheet is removed from form, and the excess plastic is trimmed from around the "shape" using a bandsaw, router, etc.
Both are pretty simple processes, but it takes a fair amount of trial and error to get the temperature right and refine all the other details of the process to get consistent results. 

Regards,
Scott Hanson
----- Original Message ----- From: "Brian Foley" <ka1bbg@xxxxxxxxxxx> 
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Tuesday, March 18, 2008 11:52 AM
Subject: Re: [TCML] Bending acrylic



Hi, i am not an expert but a plastics shop nearby i had seen them forming
4x4 foot sheets of acrylic.....2 things, first they run the sheet into a
heat lamp oven until is is soft as butter, then it is moved, floped over
onto the vacuum frame and sucked to that shape, once cool it remains in the 
shape of the mold....
you need to heat a wide area around where the bend will be and support that 
wide area while it is soft....be careful of overheating, fumes are noxious
and the stuff burns real easy once at melting temperatures.....cul brian f. 


     www.genapro.com
----- Original Message -----
From: "Scott Bogard" <teslas-intern@xxxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Tuesday, March 18, 2008 12:16 PM
Subject: [TCML] Bending acrylic



Hey guys,
    Since we have had a few machining/finishing questions on here
lately, I figured it would be ok to ask; is it possible to bend acrylic
and get it to hold it's shape.  I want to make a curved piece of
acrylic, and it seems fragile and wants to crack.  I'm assuming you need
to heat it, but how hot, using what kind of heat source, etc.  Thanks in
advance.

Scott Bogard


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