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scooter
11-03-2004, 11:06 AM
Can someone give me a method of stress releiving acrylic - I assume you would use an oven. I have pieces of tubing glued together and machined and I would like to relieve the stress in them to reduce the chance of these breaking and coming apart.

Thanks in advance

Ted Coffey
11-03-2004, 11:41 AM
Its pretty involved. Part must be supported to prevent sagging.
After cementing allow at least 24 hours drying time before annealing. Annealing temperatures are around 180 degrees Farhrenheit. Heating and cooling must be slow and preferred to be done in an air flow oven. Heating rate is 22DegreesF/Hour.
Cooling time is about 10 hours from 180 to 140 degrees. After reaching 140 degrees the part can be removed from oven and allowed to cool to room temperature.
Ask your supplier for a Acrylic Fabrication manual which will have this information.

[This message has been edited by Ted Coffey (edited 11-03-2004).]

[This message has been edited by Ted Coffey (edited 11-03-2004).]

[This message has been edited by Ted Coffey (edited 11-03-2004).]

Forrest Addy
11-03-2004, 01:13 PM
I suppose 1500 degrees is too much.

chkz
11-03-2004, 03:49 PM
lol Forrest...that might be a bit over the top.

I made up an acrylic camera housing with some glanded holes for operating the camera...kind of an underwater "experiment"...was using 3/8 sheet...its not easy to get the temps right for bending, etc...(maybe it is with the right gear rather than a hand held heat gun) and end up with a nice finish. I didn't have much luck but then i didn't spend alot of time researching the thing. I did get some "special" gluing solvent of some sort from the guys who sold me the scrap acrylic...forget what it is/ws called now but you had to keep it in the freezer (evaporated at room temps pretty rapidly)...good luck with your project,

Chris

wierdscience
11-03-2004, 07:32 PM
<font face="Verdana, Arial" size="2">Originally posted by Forrest Addy:
I suppose 1500 degrees is too much.</font>

But the black smoke would be an indicator that your using too much heat http://bbs.homeshopmachinist.net//biggrin.gif

chkz
11-03-2004, 10:06 PM
like welding aluminum eh? two temps....not quite hot enough and wayyyyytoo fu***ng much heat....

darryl
11-04-2004, 03:27 AM
I have not previously been aware of the annealing temps and method that Ted speaks of, but what I do like to do before cutting and fabricating in plexi is to pre-shrink it. It does need to be supported while it's soft, and for tubing, hanging it would seem to make the most sense. Most ovens aren't going to be able to take a very long piece vertically, but -
Anyway, a temp of about 300F is required to soften it enough to pre-shrink, and when done, flat material becomes thicker and smaller in length and width. I suspect tubing will increase in wall thickness and shrink in diameter, and may even curl in it's length, or go out of round. Flat sheet can be kept pretty close to flat, but chances are that it will not be as accurate a surface as before heating.
Anyway, this gives it a better dimensional stability over it's lifetime, especially if it's going to see sun or higher temperatures than normal.

jcurrell
11-04-2004, 09:15 AM
The main problem of cracking is the martrial. Cast is for glueing.!!!! and much more expensive.extruded is for non glue aplications.

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