Build a plastic heat bender or Nichrome controller

Community General Discussions
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I am attempting to build a thermal plastic bender to create mounts and parts for my robots.  Basically a piece of nichrome wire heats up a small area of the plastic which allows me to bend/form it by hand.  The nichrome wire I have, came out of an old space heater.  It is formed into 1/4 inch coil.  I don't have a clue to the metal contact or diameter (pretty darn thick since it was an old heater.) 

 I tried connecting it directly to a 12v 2.6 Ah SLA battery.  A short section of about 6 inches coiled.  The direct connection proved to be too much current and almost instantly brought it to a bright glow.  Probably 2-3 seconds before I disconnected it for fear it would burn out. Much to hot to use for plastic forming... Smelting gold,  maybe :-) 

 The examples of the bender I  have seen use a variac transformer to control the current.  I don't  have one, so my question is,  will an adjustable power supply using a variable resistor / lm350 circuit have the same type of control 'dimming'/reducing the heat (or am I way off on the concept here?)  using a circuit such as this: http://diyaudioprojects.com/Technical/Voltage-Regulator/

I am learning as I go, so I may be totally off in this application.  But it seems it would act the same for a dc battery driven circuit (instead of an ac driven variac transformer.) 

Here is what I  think needs to happen. 

The original heater had a type of thermostat to control the heat.  Heat sensitive wire would allow contacts to close and send power to the coils.  A type of mechanical voltage control.  I can't place this 'thermostat' into the project.  It would interfere with the plastic being above the heat source.  So I  am attempting to control the heat radiated by reducing/increasing the voltage to the heating element. 

Thanks for any assistance. 

Ed

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It occurs to me…

You may want to take a look at 3d printer software. Its a bit overkill, yes, but something like Teacup will run on a regular arduino (328), can read a thermister (2, actually) and also control 2 mosfets to control the heat. All the PID stuff is done, it works great to control the temp of extruders and heated beds.

Again, overkill in that you would not be using any of the “CNC” part of the firmware, but it is an off-the-shelf solution, free, well documented and will do what you need it to.

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I am eventually going to

I am eventually going to build a 3d printer from scratch (as opposed to a kit).  I’ve been collecting old inkjet printer and flatbed scanner parts with this in mind.

My next project is planned to ne a plastic vacu-form bed.  So I  will definitely be taking a look at this.  May just advance the timeline of my plans. 

ED