Let's Make Robots!

Plexi Bender 800 (aka Plexiburn Gnomeatron)

Hopefully, bends plexiglass for robot making.

After seeing a video of Jeri Ellsworth's plexiglass bender, I decided I wanted to make one.

I had an old baking pan that was retired and just waiting to become a project. I used that as the base, since Jeri's version scorched her benchtop. I included a power switch and indicator, and a 10 amp fuse as well. Other than that, it is basically the same.

Aluminium u-channel is used to hold the heating coil from an old hair dryer. I got mine for free from craigslist.org. It was a 1600 Watt dryer, and I took one of the two main coils. So I figure my bender will run at about 800 Watts. Thus, the Plexi Bender 800 is born.

But will it work? The plaster of paris that insulates the coil from the u-channel is still drying. I should let it set for 24 hours. Luckily (?), I'm feeling a bit under the weather tonight, so I should be able to sleep through a lot of the waiting.

I'll post an update after I test it. If it works well, I will post detailed instructions (possibly on Instructibles.com) on how I made it. I took lots of pictures during the build.

Update 2011-04-13... Later that same day

With some practice, I found I can use the Plexi Bender without modification.

Above is the servo mount for Why Tri. It came out really well, if I do say so myself!

Update: 2011-04-13

I tested the Plexi Bend 800 this morning, and it definitely bends plexiglass. Unfortunately, it also melts plexiglass. Sometimes, it sets plexiglass on fire!

Some practice with the bender taught me some things. I can make bends without melting the heck out of the plexi if I hold it higher above the coil.

In the picture above, the smaller piece of plexi at the bottom of the picture shows my first two bends. These two were laid right on the u-channel, and practically melted all the way through the plexi.

The larger piece has a set of bends where I started lifting the plexi above the heating coil. The bend at the top-left was the last bend, and you can see I managed to bend it without any bubbles or deformations.


So the bender does work, but needs some improvement.

Needed Improvements

In the picture above, you can see that the heat of the coil actually caused the aluminium u-channel to expand. Since the u-channel is mounted with screws at each end, it bowed upwards in the middle. I need to cut mounting slots instead of round holes, and allow the u-channel room to expand.

Most importantly, I need to be able to vary the power sent to the coil. I'll have to check into the best way to do that. I have a couple of high power variable DC power supplies, but they need repair. I'll either need a dedicated way to vary the power on the Plexi Bender, or I need to fix my power supply and use its variable DC output (up to 37 Amps) to run the coil.

Working Well

One thing I'm very happy with is that the thermal insulation between the coil/u-channel and the baking pan works great. The pan was just warm to the touch, while the aluminium of the u-channel was hot enough that it dented when I pushed it back into place with a tool after shutting off the coil. The two pieces of wood were only an inch or two away from the u-channel, and they were only warm to the touch.

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Actually, that article explained it:

"The drop in voltage required for the DC fan motor is achieved by connecting the low wattage heaters in the heater box in series with the fan motor leaving the high wattage heaters connected in parallel or non-series to the motor."

I sort of expected that, but it was nice to see it confirmed.


Note to self: This blog from The Mechatronics Guy has some good info.

I really have to get back to this project some time soon.