Positioned the filament inside the plaster trough, and secured the ends of the cables with wooden wedges:
This weekend I decided to make an acrylic bender. I got the idea from a video on the internet.
All in all, I was impressed by the design of the hairdryer. The heater seemed to run in series with the motor, there was what looked like a bi-metallic thermostat that would cut out if the outlet was blocked, and there was a non-resettable thermal fuse as a last resort. It seems like that it would be quite difficult to start a fire or do damage with this.
I cut a piece of aluminium U-channel to length, then used hot-glue and scraps of wood to seal the ends up. Mixing some plaster (50g plaster, 35g water) and pouring it into the trough made a nice heat resistant, electrically insulating base to run the wires on.
My unit has approx 14" (35.5cm) of usable length, and I intended to use a 24V power supply.
I decided to start with 16 Ohms and work from there.
Photo of the parts:
One more thing to consider is that when it heats up, the filament expands dramatically. Since in this case I have it in a conductive channel, that's a little alarming. Pay attention to the length of cable you need.
First I ran with about 16 ohms of resistance (equivalent to the 90W strip heater above). This heated up a bit, but was way too cold for bending acrylic. To give you an idea, I was able to hold my hand flat across the opening for more than 15 seconds.
I powered down and changed the length of the filament to be about 8 ohms. This worked much better.
I was also able to bend a larger sheet (~20cm wide) in a right angle too. However when I tried to heat it up and bend it flat again I cracked it. Opps.
It may be possible to solve both these problems by just using some straight nichrome wire. Unfortunately this means I send an innocent hair-dryer to its doom for no reason.
My previous method for bending acrylic was a heating gun, and would often leave bubbles and discolourations in the plastic. This works much better.