Electrolytic Derusting

Post date: Jul 20, 2015 12:59:14 PM

I bought a table saw that had been neglected. I saw (get it) this as an opportunity to try electrolytic de-rusting. Here is a picture before the process and a picture of it suspended in the bath. Also shown is an ATX computer power supply that I "converted" for use as bench supply. It supplies 5V to the bath. A 3lb box of washing soda was used in the bath. A 20 x 30 inch stainless piece of sheet metal was used as the anode. The table top was connected as the cathode. I used beam clamps to attach the power supply to the electrodes. I have been running 20A through the bath for about 5 days. I started with the whole saw top, but pared it down to just the center section for the last half of the time to get it done first and thoroughly.

I hooked an ammeter inline with the power supply to monitor current through the bath. It is pretty important. Without it I am sure I would have overloaded the power supply. I adjusted my current DOWN to 20A by using the resistance of the steel chain. I kept moving it up the chain until it got down to 20A. The bath is a frame of 2x4 lumber with a tarp thrown over it.

If I were to do the power supply to bench supply conversion all over again (and I won't), I would have used an old power supply fan and housing instead of the junction box. I would also recommend anyone thinking about this conversion to use an ATX extension cable to provide the connection to the box. Reasons? Because and old supply will have the fan already mounted, has ventilation slots already, and it is the exact same size. The ATX extension cable only costs about $2.50 on ebay delivered and saves A TON of soldering to pins, which in my case, broke off later. The fan is needed to dissipate the waste heat from the resistors used to load the power supply to keep it happy. Without it the junction box gets uncomfortably warm (140F). I have 5.4Ω connected to the 5V side to keep about an Amp of idle current. I have 3.6Ω on the 3V line, and I have 21Ω on the 12V line. Total dissipation inside the junction box was about 14W. The box is a 4-11/16" square x 2-1/8" box.

I am also putting new bearings into the saw. They took about 1/2 hour to remove from the saw. They took about 20 minutes to put in. Very easy.

The results of about 4 hours of of work cleaning the "black rust" off the saw and then applying Johnson's paste wax to seal the cast surfaces in can be seen below. The sun makes it look a little better than it does in real life, but it is worlds better than what I started with. Some of the pits in the top were as much as 0.015" deep. Although the purists and archaeologists would not recommend it, a fine wire brush to reach down into the pitted areas to clean the black rust out helps a lot. I found they were too deep and small in diameter to get it all with the 3M metal finishing pads. Areas that just had surface rust on them cleaned very easily with the finishing pads. No more effort than washing a cast iron pan with stuck on egg. I ran about 15-20 Amps through each of the three sections of table for at least 2 days. I found that I dipped them and cleaned them about 3 times. I don't know if the intermediate cleanings were really needed. I just couldn't keep from messing with it and checking its progress.