The contact points of our Harbor Freight spot welder had gotten too pitted and damaged to work. I had no luck getting replacement parts from anywhere, so I made a replacement set. I used TechShop San Jose's lathe to make the parts.
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Step 1: Load Copper Rod Into Lathe With Collet Closer
I bought a nice copper rod from McMaster-Carr - it wasn't cheap, but it was less costly than a new spot welder. The piece was 3/4" in diameter, so I used a 3/4" collet to hold the rod.
Step 2: Cut Thread Side to 8mm
The threaded part of the tongs that the tips screw into are 8mm, so the plan is to cut the copper shaft to 8mm.
Step 3: Cut Angled Tip
Using a triangular cutter, I shaped the front of the part to resemble the bad one I had taken off.
There is no need to part the piece, as it will pop off when you get mostly done shaping.
Step 4: Thread the Back Side
I used a die to thread the back side. Shiny!
Step 5: All Done!
Install the tips and weld! The originals had flats to use a wrench to install them, but a pair of pliers or vice grips works fine.