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Need help with simple heater board wiring specs

 
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samspade



Joined: 12 Sep 2015
Posts: 1

PostPosted: Sun Sep 13, 2015 5:58 pm    Post subject: Need help with simple heater board wiring specs Reply with quote

I need some help designing a heater element to use to with a sheet of plexiglass...

The plexiglass is OPTIX brand .08" thick and measures 44" x 11.5" when flat. I need to evenly "bow" the 11.5" inch side so it becomes 10" wide (with a bow-height of 2.5"). (This will be used to form a clear window on a 'sleep-chamber' project.)

I plan to achieve the "bowing" by making a 'large-jawed clamp' using two wooden 2x4s that are 45" long. I have drilled three holes down the lengths of each 2x4 and inserted allthread rods & nuts between them. When the nuts are tightened with the plexiglass in between them I achieve the desired "bowing" result, as shown below:

Code:

      ___                     ___
     |   |sheet of plexiglass|   |          < flat .08" plexiglass sheet
====:|2x4|===================|2x4|:======   < allthread rods & nuts (loose)
     |___|                   |___|
 
                     
      ___      of plexi     ___
     |   |sheet       glass|   |            < bowed-up .08" plexiglass sheet
====:|2x4|=================|2x4|:========   < allthread rods & nuts (tightened)
     |___|                 |___|
         
         |++++ heater +++++|                < need help with this part!


But I need to heat the plexiglass to about 300-350 degrees fahrenheit so it will permanently keep the desired "bowed" shape when cooled. To provide even heating and keep the design as simple and cheap as possible I'm thinking of something like the following design:

Code:

+-----------------+
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|  |_| |_| |_| |  |
|              o  |
+-----------------+


I plan on using a sheet of concrete backer board with a heating area measuring 45" x 9". I'd like to use a continous piece of straight nichrome wire to form about ten 45" runs as is is available cheaply on ebay. (If there is really a big advantage to using "coiled" heating wires, please let me know.) I figure there will be about 2"-5" inches between the top of the heating elements and the underside of the curved plexiglass when assembled to the bottom of my 2x4 'clamp'. The heater doesn't need to be built for longevity as I only need to make a couple of curved plexiglass pieces and then it will be discarded.

And that is where my plan is stalled...

As stated previously, I'd like the heater to develop about 300-400 degrees fahernheit over the 450" total of straight wire but I don't know what type of wire (nichrome60, nichrome80, kanthal, ect.), what gauge and/or what resistance-per-foot?

Given that I'd like to plug it directly into 115vac and achieve 300-400 degrees using 450" of the heater wire can anyone help me with the specs? (And of course if anyone has design improvements please let me know as well.)

THANKS SO MUCH!
-Sam-
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Fredo
Expert


Joined: 21 Mar 2007
Posts: 246
Location: Kingdom of Nye Area 51

PostPosted: Tue Sep 15, 2015 1:58 pm    Post subject: Reply with quote

I think you're going to need a form to slump it over to keep the shape when its soft... You might be able to use a propane shrink wrap heater and heat the plastic until it softens enough to take the shape of the mold with no clamping.. Have never done any Plexiglas shaping or bending so i'm just guessing here...
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If someone has a gun and is trying to kill you,
it would be reasonable to shoot back with your own gun...The Dalai Lama..Seattle 2001
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spektr
Master


Joined: 07 Jan 2008
Posts: 425

PostPosted: Sun Nov 29, 2015 1:50 am    Post subject: Reply with quote

Sorry im so late here BUT here is the way to do it easily......

Use flannel stapled to the tops of a couple 2X4's to make an unsupported hammock for the plastic to slump into when soft. clamp the 2x's to a table so they dont move around...... Lay the plastic on top of it cold. Grab your spiffy infared 11000 btu heater and go back and forth over the plastic until it softens and lays into your flannel channel. I use a lot of soft moldless molds when its a straight comtour. Flannel leaves no marks unless u abuse the process.......
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