Gauge Blocks

Jason,

According to Wikipedia:

The minimum conditions for wringability are a surface finish of 1 microinch (0.025 µm) AA or better, and a flatness of at least 5 µin (0.13 µm).

^MichaelG.

Edited By Michael Gilligan on 01/11/2014 18:57:52

Michael - I think that my photos show that your "cheese" exists, I am having difficulty in understanding the point you are trying to make.

Rik

Rik,

My point is that there appears to be widespread confusion in this thread.

Andrew made the entirely valid point that there is an "oil film" on each surface of a "wiped-clean" slip, and that the nominal thickness of the slip is reckoned to include one of these.

I don't think that either of us has suggested applying a thick layer oil ... it simply needs to be recognised that the film exists.

MichaelG.

Forgive me for laughing and I know that I contributed to this thread but Jack only asked what they are for. Bet he regrets asking.

PhilH

Just in case any Brit. is concerned by the use of NIST as the Authority ... here is a page from our own National Physical Laboratory.

MichaelG.

.

P.S. ... good point, PhilH.

And to the OP Jack Foreman 1:

"Can someone please explain what Gauge Blocks are?
And what are they used for?"

What do you think of it so far?

Rik

Well someone who bought a set recently got a manual with them and sent me a copy.

It runs to 174 pages

Nearly as long as this post and twice as long as waiting for Crown solo paint to dry.

Are ceramic slips a different size from steel ones as no oil film need be present? Just giving the pot a stir!

Mike

It ensures the surfaces are free of dirt, you could use water but it would promote corrosion, you could use a degreaser but that would remove any surface corrosion protection.

The assumption that the presence of oil will affect dimensions is bunk, if the metal has close enough contact to "wring" it will do so, if something is preventing intimate contact it will not "wring"

I spent an entire Summer Holiday calibrating micrometers to ISO 9002 for IMI Leeds

.

Nick,

Did you look at the NPL page that I linked earlier ?

[quote] It is found that phenomenon of wringing occurs due to molecular adhesion between a liquid film (whose thickness may be between 6 to 7 x 10-6 mm) and the mating surfaces. [\quote]

Whether 6 to 7 millionths of a mm is relevant depends upon what you are doing; but both NIST and NPL do make allowance for the film thickness.

MichaelG.

Hey lads

As a metrologist I can assure you that removing the oil is correct. The slip gauges ring together due to there surface finish which stops air from entering between them. There are three types of gauge block or slip gauges. Workshop,Reference & standards.

Slip gauges have very little use outside a metrology lab because of temperature when you handle them. Although they are used with sine bars it depends how accurate your tolerance is. If it is in tenths and you handle them you will blow your tolerance. The gauge blocks are set for 23 Degrees C and your fingers are approx 37 C. The main use for the slip gauges is for calibration of measuring tools but are occasionally used in the workshop with the ambient temperature in mind..

Regards

Larry

Edited By Larry Coleman 1 on 08/01/2015 11:04:35

I don't follow that? If I understand correctly, for slip gauges to be wrung the surface finish needs to be better than about 0.025µm, or 25nm. Let's assume that we achieve a 10nm finish and it is Rz rather than Ra. I think that a nitrogen molecule is on the order of 100pm, or 0.1nm. So two orders of magnitude smaller, so I don't see how air (mostly nitrogen) can be totally excluded?

What happens if you try and wring slip gauges together in a vacuum?

Andrew

Gentlemen,

When I did my apprenticeship over forty years ago we had a very good toolmaker turned apprentice instructor who could be very pedantic in what he did or said but you couldn't fault him, one of the best.

He taught grinding etc mostly and when we had to use Slip Gauges/Gauge blocks he drove a routine into us, when opening the box you cleaned each slip to remove the oil before they were rung, after using them you wiped them over with a lightly oiled cloth to remove finger prints and dirt before they went back in there place in the box, when in use they had to be kept on a piece of Baize away from your work unless being used.

Martin P

Well what you say is correct in some ways but I assure you that the surface finish on a good set of slip gauges do not need oil on them. In the metrology lab when I worked for Hawker De havilland we had the most sophisticated metrology lab in Australia and the slip gauges were checked by optical flats which are polished quarts slabs and were viewed under sodium light. Both the slip gauges and the optical flats were extensively wiped clean of any oil with a special cloth. Yes Andrew the finish is that good. Slip gauges should not be left rung together for long periods.

There is a process called metal flow and they can be difficult to separate without damage. This is why air craft parts have a shelf life. I have never seen it in the lab but I have seen it in aircraft parts many times.

In regards to the vacuum I have never tried it even though we had a good vacuum chamber for environmental tests. That would be interesting & when I get my orthoclave working I will see if a suction cap will work in a vacuum.

Larry

If folks follow up some of the references given earlier they will see that it is impossible to wipe a surface completely free of oil with any kind of cloth. There will always be a molecular film left that will make a tiny (sub-optical) difference to the thickness and probably contributes to the adhesion process. I doubt that any of us in our hobby-lives will ever find a situation where a wipeover with a clean rag before use wouldn't be good enough.

Neil

If you look at a ground and lapped surface under a strong microscope it appears to be like a mountain range, if it had oil on its surface then any molecular film would fill the gaps allowing the larger raised area to be "oil free" after a clean.

Martin P

This argument. Re oil film on slips seems at least 90 years old.

Npl tests in 1924 explored the effect of different oils of minimum thicknes
And looking at the difference in height of a given pair of blocks....
See attached

It seems the oilfilm may reach zero thickness on the high spots of the finish and more in the valleys. .how the high spots of one slip interact with the lows of another slip might also add to the "grip"..
The effect of air pressure on wringing was also explored...
And at 0.5 psi the force to pull apart tge slips exceeded 30 times that from the air pressure.
..will attemp to post extract

Edited By jason udall on 08/01/2015 17:49:35