Restoring a Vernier Gear Caliper

Good morning all, could I please ask for some advice about de-rusting and preserving a set of gear calipers I bought recently.

As you can see, they are dirty but also they have minor rust marks.

Do I:

1. Leave well alone, just oil them and store them in VPI paper

2. Clean them in say IPA or brake cleaner, oil and store as above

3. Selectively scrub at the obvious rust and then oil etc.

If option 3, what is appropriate abrasive? I'm thinking 1000 grade wet or dry glued to one of those coffee stirrer sticks from Starbucks. Steel wool is another possibility, scotchbrite seems to me to be a bit too aggressive.

Your advice please?

Thanks as ever Simon

Superfine steel wool and WD40. But not around the etched lines and numbers.

The numbered and lined scales can be rubbed on a piece of fine wet rub paper stuck to a glass plate, or on a nice new flat oilstone. I just fixed up my old M&W 6" toolmaker's ruler this way. Came up like new.

Nice bit of kit BTW, and worth lavishing a bit of care upon.

Edited By Hopper on 06/05/2017 11:06:14

Citric acid and hot water Simon, I decided to try this routine after reading forum posts of people raving about it, they're not wrong, I've wasted years of my life hunkered over sandblast cabinets & rotary wire brushes, but this stuff really is the dog's nuts, it's cheap as chips and can be tipped down a drain when spent, so good in fact I'm starting to run out of rusty bits to clean

Test it first though, to make the citric acid does not dissolve the black etching/marking material in the engraved lines and numbers. That;s why I used the oil stone on my ruler, it polished the main surface but left the black lines and numbers untouched.

I like to first coat or soak the disassembled tool or part with paraffin oil and then try and remove as much loosened oil and rust as possible, Depending on the degree of rusting and the nature of the surface to be cleaned that can mean anything from steel brushes, various grades of sandpaper and/or steel wool, to scrubbing with an old toothbrush.and working into corners with toothpicks. In the case of a precision tool like you gear calipers I often use a diamond sharpening card to clean off the surface rust. Unless the etching is very fine it won't be disturbed by the diamond card. Be aware however that the surface appearance will be changed from the original since you are now undoubtedly using a different grit and if the original is a pickled finish you will be changing it You may also be surprised to find that the original non.bearing surfaces are not particularly flat so as you work over them the newly finished areas expand in patches until the whole surface is leveled. If you are not willing to completely level the surface the resulting look will be most peculiar. Rather than that it would probably be best to just get off the surface rust with the gentlest treatment possible. As Hopper suggested you can use an oilstone to finish. I use razor hones quite a bit for final finishes. Should you use oilstones on flat surfaces they should be flat, not difficult to do using the three plate method. With a pair of oilstones you can get all four large surfaces flat with a little persistence, or even all twelve surfaces if you are so inclined, using nothing other than the stones themselves. I don't care for abrasive papers for anything past initial rust removal. I at least find it too easy to slightly round off corners if the paper is just laid on glass. Gluing the paper down is troublesome and doesn't give me the flat abrasive surface I would like. .Be very conservative when it comes to the actual measuring surfaces and bearing surfaces. If they are still true with only a slight bit of rust certainly nothing more aggressive than 0000 steel wool to just clean off the surface rust is called for. You will find wire brushing does a nice job in cleaning the knurled surfaces of the adjustment and clamping screws. As Hopper mentioned, citric acid has the potential to lift the filling out of the graduations and the numbers. While refilling the etched markings isn't particularly difficult, if you have left rust pits and rough areas on the surface, it is likely that they will to some extent get filled along with the engravings and you will have quite a time trying to remove the unwanted filling while leaving the filling in the engravings in place. As a final step I like to take the disassembled parts, gently heat them to drive off the surface moisture, coat them with a microcrystalline wax, let dry, buff and reassemble. The wax treatment seems to give good protection but only if the surface moisture is driven off first. Otherwise you may find rust redeveloping. Wiping down with lanolin is also a good approach as long as the tool is not kept on a surface that wicks the lanolin away. Have you ever tried Camphor in your tool boxes? I find it effective and far more convenient than keeping every individual tool in VPI. If you have any less valuable tools with a bit of rust, perhaps even an old sawblade or a trowel lying about, you might try some of the above approaches, citric acid, sandpaper, stoning, or steel wool and WD40, and see which give you a pleasing result, before starting on a somewhat rarer item.

Well, than you all for your expertise, and for such exhaustive advice.

I have gone for the conservative conservation approach, gentle abrasive and cleaning with solvent. Here's the results so far:

I think (though I'm not sure) that the graduations are engraved not etched, and I don't think they are filled. Under a hand lens I can see that they are indented into the surface, but not by much and they seem to be a change in texture more than a contrasting colour. In any case I could foresee difficulties as suggested in possibly etching the surface finish - so I have gone at it gently with 1500 grit wet or dry used mostly dry but wet where it needed a bit more attack, and clean with brake cleaner. The W&D paper was a thin strip glued to a lolly stick, this gives a good compromise between being too flat and only touching the high spots or rounding the corners of every surface.

I cleaned the knurled surfaces with one of those horrid mini wire brushes in a Dremel.  Saying to myself as I did so "please don't let this catch and throw it across my workshop..."

For the time being I've just oiled the caliper again to reduce the chance of my sticky finger prints rotting the surface, but I'm keen on George's micro-crystalline wax idea. It's a lot more practical than trying to keep things wrapped up in VPI paper.

So I think I'm going to quit while I'm ahead, maybe coat the caliper with something but I've done as much abrading and scrubbing as I want to. They'll never be new, but at least they are readable. I just need to re-calibrate the zero's for the vernier scales - I took both off to clean underneath them and I haven't got then absolutely bang on the right position again yet.

Many thanks for the advice, as ever the expertise available is second to none.

Rgd Simon

Edited By Simon Williams 3 on 08/05/2017 12:02:24