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I just recently purchased an old, 1945 era, cast iron craftsman table saw off Craigslist for $25 with the intent to clean it up and restore it. You get what you pay for and it’s heavily rusted. I’ve been reading all over the internet about different methods for removing rust (elbow grease, scotch pads, vinegar, electrolysis, etc) and to do a thorough job I think they’ll all require dismantling everything down to the bone first. Hoping to skip that dismantling step I was wondering if it would be a good idea to submerge the entire machine in electrolysis to remove it in one fell swoop. Worth pointing out the motor/anything electrical is separate and wouldn’t be submerged.

Any reason I shouldn’t? Any bearings/etc that would be damaged by it? Other reasons you can think of?

Similar question: would it be safe to submerge it all in similar derusting solutions (vinegar, etc)

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Hoping to skip that dismantling step

Let me dash that hope first (sorry!) you're going to need to do some dismantling.

You have to do some, and to do a really thorough job you have to take it down to individual pieces. Not doing this (with anything, even something as mechanically simple as a hand plane) is doing a half-assed job of it.

The reason you need to do at least some disassembly is that all rust-removal processes require access to the rust. And nothing can magically reach inside the gap between a nut and its bolt, or any screws and the threaded holes they go into1. Two pieces that only press together tightly can be treated for days or weeks and have the rust between them be completely unaffected.

So to do this properly you need to separate things.

I was wondering if it would be a good idea to submerge the entire machine in electrolysis to remove it in one fell swoop.

No. It won't work, at least not the way you're visualising.

Apart from certain technical difficulties trying to do this on something of this mass, electrolysis has a certain line-of-sight effect between the part and the sacrificial electrode(s). While this problem can be exaggerated by detractors of the method it is undeniably a factor, and it means that internal surfaces, hollows and of course the small gaps I mention above will get little or no rust removal while the externals get clean.

What to do instead?
For something of this size I suggest a molasses bath as a cheap, safe (for you and the rusty object) and effective alternative. Here's how effective:

Molasses bath before and after

For large-scale rust removal like this molasses solutions are hard to beat in terms of cost effectiveness. Other than the smell2 the only real downside to this method that I've seen is in the speed. It's slow. But why be in a rush?

Some notes:

  • As with all rust removal processes it's a very good idea to clean the thing reasonably well before you start. Brush off any loose rust while you're at it. Most important with chemical rust removal is to degrease as much as you can because any significant oily or greasy surface deposits will slow or prevent the chemical from being able to act on the iron and steel.

  • As with all chemical solutions molasses solutions are more effective at higher concentrations. You'll read various dilutions given online (10:1 and 11:1 seem to be popular) but my experience and that of others has shown it still works far more dilute than this — 20:1, possibly lower. Which is handy for something of the size you're dealing with!

  • As with all chemical reactions it goes faster at higher temps but it's not vital that the solution be kept warm, a molasses soak does continue to work in the cold. I've had continued results at maybe 2-5°C (35-41°C) on a cold windowsill in an unheated room, however it is noticeably faster in the summer.

  • It's a relatively slow method at the best of times. For heavy rust deposits think weeks not days.

  • Your molasses solution can be used many many times before it's exhausted, some even suggest indefinitely. I've never had the chance to test this out myself but I have kept a bath going for over two years and other users report they've had theirs up and running for much longer.

  • In the US a common source of molasses cheap in bulk is at somewhere like a feed store.


1 If there even is one! Bad rust tends to have closed this gap, which is precisely why rusted bolts and screws are so hard to unscrew (even when they go into wood, where there's no "rust weld" effect).

2 Some people don't mind it so much but it is strong and if you don't care for it will be a little off-putting. But you don't have to be around it much because as soon as the thing is fished out of the solution you'll be moving it to one side and hosing it off.

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  • Molasses probably works because of the presence of Oxalic acid -- any acid would work to some extent since iron oxide is a base. Soaking things with rhubarb leaves would also do the trick! I've never tried molasses because I need fewer reasons for critters to visit my shop or basement, and I hear it's a bit slow. Evapo-Rust makes a gel formula that is good for derusting larger objects that aren't convenient for breaking down and soaking. It works by a process of chelation, so it is a bit faster. I imagine the cleanup would be easier, as well. – jdv Jan 14 at 16:35
  • There are different mechanisms posited for the way molasses works, some claiming it's a natural chelator — some point out that Evaporust smells a little like molasses. I've never bought any so have no idea if this is so. Other say the process of fermentation of the solution produces phosphoric acid (not that it's there beforehand). However, I don't think that can be right because you can use straight molasses for derusting surfaces, which strongly suggests whatever the active process is it's not a byproduct of the fermentation. I suspect myself that it's more complex than anyone realises. – Graphus Jan 15 at 6:55
  • Evapo-Rust doesn't smell like much, but it certainly does not smell of molasses! One hint that chelation is happening is if you see interestingly coloured crystals on the objects. Chelation will sometimes cause bright yellow (or off-white) oxides to recrystallize out of the solution (which can just be wiped off if it ends up on the objects in the bath), These colours correspond pretty closely to the various mixed oxides and phases (maybe hydrates? -- my organic chemistry is weak) that iron oxides can form when reforming bonds. – jdv Jan 15 at 15:13
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If the blade tilt and elevation work or can be freed, cleaning the top with fine (220 or so) and random orbit sander, I worked well on mine. I really do not know if it would damage the bearings probably not good for them but??? you would defiantly have tore lube the threads on the tilt and elevator shafts. I am assuming that it is a "100" series they are a fine saw the rip fence is not good. I have 2 100 series saw and use it to do fine woodworking motor upgraded to a 2 hp new rip fence and miter gauge, The bearings may have to be replaced not hard just a little tedious. It beats any new saw you can buy for $800 or less.

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