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Slip gauge question.

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Tifa 857216/01/2022 23:27:58
33 forum posts

I've been given a subsatntial slip guage set. A very greatfully received freebie.

Dozens of guages, made in the UK, certified, imperial and in a nicely made quality wooden box.

But.....the previous owner hasn't stored them very well, and on a few there's some surface rust.

My questions are.....are they now junk? And if not, what's the best way to clean and preserve them please?

Any advice would be good.


Emgee16/01/2022 23:39:37
2404 forum posts
285 photos

If the rust is not on the measuring faces there should be no harm done by using some removing agent, if the rust is on measuring faces then removing any amount of material will put the gauge out of spec.


Paul Lousick17/01/2022 00:16:30
2009 forum posts
711 photos

What level of precision do you work to ? Do you measure with a vernier caliper or micrometer ?

They are probably OK for most hobby applications where you do not need toolroom accuracy.

Tifa 857217/01/2022 00:26:11
33 forum posts
Posted by Paul Lousick on 17/01/2022 00:16:30:

What level of precision do you work to ? Do you measure with a vernier caliper or micrometer ?

I use both.

But I'm not good enough to be one of those super precise guys!

Aware that the damage has already been done, now at a bit of a loss as how best to tidy them up.

Brasso/soft cloth? Probably shoot the accuracy out of the window, but providing I mic up every time before use, and don't rely on the stamped sizes?


Edited By Tifa 8572 on 17/01/2022 00:26:51

John Ockleshaw 117/01/2022 03:03:04
53 forum posts
7 photos

Hello Tifa,

Try to get some inhibited phosphoric acid, may be rust remover from automotive paint suppliers.

It converts the rust to iron phosphate, which can be scrubbed off with a nail brush.

It does not attack the parent steel. It offers no rust protection so keep your gauges oiled or vaseline coated.


Pete Rimmer17/01/2022 06:47:46
1219 forum posts
63 photos

However you clean them unless youuse emery they will be more usable than they are now. They may not wring but you won't be able to measure the difference even with a micrometer.

I'd be tempted to give them a couple of minutes dip in citric acid and rub with a coarse cloth. Wash and dry them thoroughly.

John Haine17/01/2022 07:03:46
4622 forum posts
273 photos


Michael Gilligan17/01/2022 08:04:55
20057 forum posts
1040 photos
Posted by John Haine on 17/01/2022 07:03:46:


dont know

Please, please; please look at my post timestamped 20/10/2021 22:44:03 on this recent thread:


… and, most particularly, follow the link to the SEM image.


John Haine17/01/2022 09:34:34
4622 forum posts
273 photos

Well I wasn't aware that some grades of Scotchbrite have abrasive powder included, but I am pretty certain that the grade they put on the back of "non-stick safe foam pad washups" does not. It will give you a way to gently remove the rust whilst hardly touching the steel surface. Another possibility is to use a glass fibre brush though it may be a little more aggressive.

Neil Lickfold17/01/2022 09:35:54
835 forum posts
166 photos

A photo of the worst rusted slip will help as to what the best way is to recover the gauge. White vinegar and salt can help to get rid of light rust. It can be micro lapped on a lapped flat piece of artificial granite square sample piece, and use 0.5 micron diamond. It will require a holder to push down onto the block, so you are distorting or lapping it on a strange shape. Seldom do damaged slips wring correctly again. They will still be useful for lots of things however. I would stay away from things like wet dry paper or even Scotchbrite.

Clive Foster17/01/2022 09:36:00
3103 forum posts
107 photos

For all practical purposes slip gauges with smooth but non wringing surfaces can be stuck together with a heavy oil or light grease. Sparingly applied and worked to extrude excess.

It will produce a positive tolerance build up but for two, three or four blocks joined together we certainly aren't going to notice.

I have a truly disgusting set of slips, found loose in the box of bits that came with a used lathe, which I use to set up the turret style bed stop on my lathes. More than good enough and I don't worry if one does take up temporary residence in the chip tray.

I also have brand new metric and imperial sets of Weber slips obtained on a whim at a price too attractive to pass up along with the two E-Bay "some wring together" bargain sets I'd previously gotten which work well enough if oil assisted.

As I also have some nanometre precision Heidenhain probes it might be interesting to set-up some tests to see exactly what the relative accuracy of the sets is in practice. I suspect the poorer sets would give rather better account of themselves than might be expected from casual thought.

But life is too short. If I put the exercise onto the to-do list now it will get to the top around 2050.


Michael Gilligan17/01/2022 10:18:51
20057 forum posts
1040 photos
Posted by John Haine on 17/01/2022 09:34:34:

Well I wasn't aware that some grades of Scotchbrite have abrasive powder included, but I am pretty certain that the grade they put on the back of "non-stick safe foam pad washups" …


yes That was the whole point of my post John

Similar to the situation with “loctite” … merely referencing a trade name is not enough !



P.S. __ This patent from the 60’s demonstrates a previous interpretation of ‘Scotcbrite’

Edited By Michael Gilligan on 17/01/2022 10:47:59

Bob Unitt 117/01/2022 10:30:36
202 forum posts
33 photos

I'm a believer in Evapo-Rust, which turns the rust into a black deposit without attacking the underlying metal, green Scotch-brite then removes the deposit leaving a clean metal surface.

Incidentally, for those that don't know (I didn't till I started turning wood), there are different grades of ScotchBrite with different grits, see -

For lightly-rusted small intricate parts I used Evapo-Rust followed by a fibreglass brush, although I'm not sure how abrasive that would be on a slip-gauge.

Michael Gilligan17/01/2022 10:51:28
20057 forum posts
1040 photos

Too late to include this with my last edit:



SillyOldDuffer17/01/2022 11:23:43
8469 forum posts
1885 photos
Posted by Tifa 8572 on 16/01/2022 23:27:58:

Dozens of guages, made in the UK, certified, imperial ...

But.....the previous owner hasn't stored them very well...

... are they now junk?...

Depends what you use them for. In tip-top condition slip gauges provide the very high level of accuracy needed to calibrate micrometers, go/no-go gauges and to make precision jigs and fixtures etc. They support the American System of Manufacture in which parts are manufactured within given tolerances and guaranteed interchangeable.

In professional use, it's vital that slip gauges be accurate. They come with a certificate, and are periodically re-certificated to confirm that ordinary wear hasn't taken them out of specification, which it always eventually does.

Slip gauges must wring together. Wringing detects faults like dings, scrapes, bending, rust etc. If slips don't wring, they ain't accurate! And even if they do wring, it's possible than one or more slips in the set is worn, and this can't be checked at home. Likely that old sets bought on ebay are out of specification even if they look perfect. All bets are off if they've been stored badly. Rust and any form of abrasive cleaning are death to an American System slip gauge.

But slip-gauges is reasonable condition might still be useful. As far as I know, no-one on this forum works to tolerances. Therefore owning certificated slip gauges is unnecessary! However, a set of uncertificated gauges could be useful for checking the calibration of our rougher instruments: even a degraded set of slip gauges is probably 'good enough' to assure ordinary digital calipers and thou micrometers are close.

Not good enough to confirm tenths micrometers. If uncertificated slip gauges are used don't pretend they prove your instruments are formally accurate though - the slip error is unknown! Luckily, being deluded about the true accuracy of our kit doesn't matter much because Model Engineers mostly make by fitting.

In the worst case, old slip gauges make useful shims and spacers. Or an interesting conversation piece.

On the subject of fitting, "quite interesting" to experiment making stuff on a lathe with simple tools, such as a steel-rule and spring-calipers.

Say you want to fit a 1" diameter spindle into a 1" diameter hole. With good eyes, a spring caliper can be set to within ¹⁄₆₄" and used as a comparator to turn the spindle. Then the hole can be bored slightly small, and opened up stage by stage until the spindle fits into it. Slide fits are easy. Judging push and force fits needs practice, but it can all be done without fancy measuring equipment.

Most things are done this way in my workshop except I get closer to 1" with a digital caliper, DRO or micrometer than with a steel-rule and spring caliper. Better measuring saves time rather than improves accuracy. I get to with about ±0.02mm / 1 thou by measuring, then I fit. What I don't do is turn the spindle to 0.998" ±0.0005, and bore a hole to 1.000 ±0.0005, and then guarantee by accurate measurement that they'll fit together!

Although I occasionally make jigs and fixtures, they're to save time on repetition work. I make them with ordinary care using ordinary methods and they're far short of tool-room standards.

In the Duffer Workshop, second-hand slip-gauge sets fail my 'fit for purpose' test. Certificated slip-gauges fail my 'Value for Money' test. And having decided I don't need slip-gauges, I spent the money on something else...


Rik Shaw17/01/2022 12:10:41
1480 forum posts
398 photos

The condition of my slips were suffering a little when I acquired them as well but I treated them to a little bit of brasso on one of those green washing up pads and that made them look a lot better. As for accuracy after such treatment?

Unless you are doing a lot of high precision grinding / lapping you need not worry. All you want now is a nice vernier height gauge to make your slips so much more useful as long as they are not jammed in the T slots on the milling table embarrassed.


peak417/01/2022 13:22:24
1671 forum posts
175 photos

Here's quite a useful little video on gauge blocks by Dan Bailey

One way of cleaning de-burring Jo blocks is to use a stone supplied by one of the block manufacturers, but that will likely cost as much as a set of second hand blocks off ebay.
This video is also worth a watch, on precision ground stones for the home workshop.

I've been meaning to make a set myself, having now fettles a little Herbert grinder; I've got some stones in stock to try, but currently suffering from inertia on that one, as I still need to make an arbor for my diamond wheel, and then a wheel dresser etc. etc.

Mr Gotteswinter's stones are not available for shipping to the UK post Brexit, so you'll have to make your own.

If you don't fully watch either of the latter two videos, note that these stones are not designed to cut on a flat surface, in the same was as a sharpening stone would, and they should also be used dry.


David Colwill17/01/2022 14:04:03
774 forum posts
40 photos

I have made precision ground stones and find them very useful. However for gauge blocks I find a small ruby stone (very cheap off ebay) seems to work very well. It is very hard, seems to be very flat and does not scratch the surface of the gauge block. As to the blocks you have, even worn they are very useful as packing and for other setups. I always pick up odd junk ones when I see them.



Samsaranda17/01/2022 15:17:45
1396 forum posts
5 photos

Is jewellers rouge any good for cleaning slips? Dave W

Howard Lewis17/01/2022 15:38:50
6005 forum posts
14 photos

For slip gauges, NOTHING abrasive should be used.

In a Calibration Room, both temperature and humidity are controlled, and the item is allowed to "soak" for at least 24 hours to ensure minimal temperature effects, before being checked.

As manufactured gauge blocks are accurate to within a millionth of an inch, which is why the conditions under which they are checked are so carefully controlled.

Their accuracy is FAR beyond what we can, as hobyists, attain.

If rust is present, it should be removed chemically, using phosphoric acid, citric acid or acetic acid, (Vinegar),

This will affect the rust far more than the clean steel.

If you use an abrasive of any sort to remove the rust, you might as well use your Micrometers as G clamps. the damage to the accuracy might well be of the same order.

It just depends on how much respect you have for precision items.


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