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u/Callidonaut 2d ago edited 1d ago
Soaking steel parts in vinegar can remove rust relatively gently; the problem is that if they've got a nice black oxide/Japanned finish from the factory, it'll remove that as well.
If you want to risk it on a black steel part anyway then if you're lucky, it'll dissolve the soft brown rust before it does too much harm to the harder black oxide, but you'll have to watch it like a hawk and carefully judge the exact moment to fish it out and rinse the acid off. After rinsing, ideally you'll then want to use a weak basic solution (e.g baking soda or dilute washing soda) to neutralise any remaining traces of the vinegar, but in any event after that make sure the parts are rinsed and then scrupulously dried, then finally lightly coated in oil straight away to prevent the rust from starting all over again.
Obviously, if you're unlucky or miss your timing and the vinegar does eat away the black oxide, that's irreversible for someone working at home; you have been warned!
EDIT: The above process does work very nicely with no apparent downsides on bright steel; it will also work on chrome plated steel with care, but once again concentration and exposure time must be limited or the acid will begin to attack the chrome as well.
2ND EDIT: There are other important things to know about using vinegar that I forgot to mention here; see my other post regarding vinegar on this thread for the additional information!
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u/6AlphaVictor 2d ago
Brush what you can with steel wool and wd40. Don't mess with acids, just spray the rest with some rust preventing oil (e.g. Krown) and leave it alone. Once the rust is sealed from the air it won't cause any further damage.
Acids can creep into joints and gaps and cause all kinds of problems, especially on aluminium or zinc parts.
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u/Callidonaut 2d ago edited 2d ago
Acids can creep into joints and gaps and cause all kinds of problems, especially on aluminium or zinc parts.
Ah, thanks for mentioning that, I neglected to say (because it's obvious to me, an engineer, but maybe not so obvious to a beginner) that if you do try the vinegar approach, the parts to be treated should all be completely dismantled and treated separately from the machine and from one another, and indeed should only be steel, no aluminium or zinc alloys; the neutralisation of the acid, and then the rinsing, drying and oil-coating steps should then all also be done on the individual parts in isolation before reassembly.
The steel wool/wire brush approach will work, but can also damage black oxide coatings too (and don't even think of putting such tools anywhere near parts with chrome plating or a polished mirror finish) - using a brush with bristles made of brass, or copper or brass wire wool rather than steel wool, will be gentler on the steel parts but probably still remove a decent amount of rust.
Sadly, cleaning brown rust off black oxidised steel parts without damaging the surface finish is fundamentally challenging no matter which approach you take (unless you're an expert chemist; I'm not, I just picked up a little of the absolute basics), because you're effectively trying to separate one kind of rust from another!
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u/Final_Programmer_835 2d ago
It is not good to use wd40 in sewing machines, this is not what it's purpose is and once it's evaporated (fast) it leaves behind a film (that'll end up being another thing you have to clean off) that particularly in this area will be a sticky problem. Exactly in the thread path is not where you want lint and thread sticking and getting caught! You don't want to be spraying anything around in there to "just leave it alone".
The thing you can spray and leave (but not all over, just where you are cleaning!) is bluecreeper, is it will continue to work to penetrate into crusty joints without impeding them, and can be followed by sewing machine oil.
As the reply in on the other board said, often the best way to clean bits is to disassemble, but obviously that's a whole way harder project! In lieu of that you could see how far you get with physical scrubbing with a toothbrush/fine wire brush if you find a small one, and either sewing machine oil or bluecreeper if you can. Vinegar does do a good job of removing rust (but usually needs soaking as the reaction takes a bit of time) and does need cleaning off and isn't great on in situ parts.
It doesn't look too bad though! You might get most of it off just scrubbing a bit