After becoming reasonably good at welding, I discovered that I really needed higher amperage than the Lincoln 175 was giving me. Particularly for welding aluminum. I sold the Lincoln and bought a used Thermal Arc welder. Unfortunately it did not come with an Amptrol. So, rather than spending $150-250 to buy one, I spent 3-4 days making one.

IMG_5766.jpg Ideally, I would have used gears to turn the potentiometer, but that would have meant spending money..

Also, I was too lazy to draw up a picture, so I made a couple mockups of the pulley arrangement first..

IMG_5769.jpg Since I didn't have a working lathe at the time, I made the pulleys on the RF40. Although getting everything lined up properly was a pain, actually making the pulleys was pretty straightforward.
IMG_5770.jpg IMG_5773.jpg Here's the turning tool that I ground out of high speed steel for cutting the groove in the pulley.
IMG_5777.jpg IMG_5783.jpg I made most of the pieces out of scrap metal I had laying around. The U bracket is a piece of square tubing with one face milled off.
IMG_5784.jpg IMG_5790.jpg The piston is a piece of 1/2" drill stock with slots milled in either end.
IMG_5793.jpg I used a piece of 2" square aluminum tubing cut in half for the side plates. IMG_5794.jpg
IMG_5796.jpg I originally tried using steel picture-hanging wire to go between the pulleys but it proved too stiff. IMG_5797.jpg
IMG_5800.jpg IMG_5801.jpg
IMG_5805.jpg Ultimately I used nylon picture-hanging wire, although eventually I got some very fine throttle cable wire which worked very nicely. IMG_5820.jpg This block is for the spring tensioning.
IMG_5822.jpg IMG_5824.jpg
IMG_5826.jpg IMG_5829.jpg The axle to hold the pedal-plate was hard to make because I used M6 screws in 3/8" stock which was hard to center on the mill.
IMG_5831.jpg IMG_5832.jpg
IMG_5833.jpg All assembled. IMG_5834.jpg It we even works so far!
IMG_5835.jpg I used a DB9 printer cable with one end chopped off for the signal wires. Here I'm soldering the leads to the pot. IMG_5836.jpg I made a cable clamp from a piece of shim stock folded over so there were no sharp edges.
IMG_5838.jpg Ready to weld!

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Text, photography and layout by C.S. Mo
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