Gauge Blocks

[John Stevenson 1Participant @johnstevenson1]

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.

[Mike PooleParticipant @mikepoole82104]

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

Mike

[Nick HulmeParticipant @nickhulme30114]

Posted by Andrew Johnston on 31/10/2014 10:05:57:

So why does Starrett recommend wiping the mating surfaces with a cloth impregnated with a light machine oil, wiping the excess oil off with a second cloth, and the wringing the blocks together?

Andrew

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

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Nick Hulme on 28/12/2014 17:15:39:

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.

[Larry Coleman 1Participant @larrycoleman1]

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

[Anonymous]

Posted by Larry Coleman 1 on 08/01/2015 10:59:41:

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.

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

[martin perman 1Participant @martinperman1]

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

[Larry Coleman 1Participant @larrycoleman1]

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

[Neil WyattModerator @neilwyatt]

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

[martin perman 1Participant @martinperman1]

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

[jason udallParticipant @jasonudall57142]

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

[JasonBModerator @jasonb]

I'm just glad that I don't have a set of gauge block and have to spend half the day deciding what rag to wipe them down with each time I use them.

No wonder we get so little posted in the Work in Progress section of the forum

J

[jason udallParticipant @jasonudall57142]

Sorry …***//PATIENCE EXCEEDED IN FORUM POST///**..
Cant get photo into message…just look at my album about slip guages…

[Anonymous]

Posted by JasonB on 08/01/2015 17:48:46:

I'm just glad that I don't have a set of gauge block and have to spend half the day deciding what rag to wipe them down with each time I use them.

No wonder we get so little posted in the Work in Progress section of the forum

J

Oh dear, I've got two sets, imperial and metric; but that's not the reason I don't generally post in the Work in Progress thread.

Andrew

[Jerry WrayParticipant @jerrywray14030]

If anyone has a technique for completely removing the layer of oil from metals I would be pleased to hear it. I have tried to remove the last mono-molecular layer when I worked on food and pharmaceutical packaging, but without success.

Any tips, the nearest we have come is washing in toluene followed by ultrasonics , using water borne and solvent borne methods. Unfortunately the water miscible systems involve wetting agents which themselves leave behind a film.

Jerry

[jason udallParticipant @jasonudall57142]

Jerry…try the techniques used in thermal deburring……atmosphere of O2 at 300 bar…apply ignition. …

[Larry Coleman 1Participant @larrycoleman1]

All very interesting comments.

When working in the Met lab the slip gauges were used to check and calibrate Go & No go gauges for production purposes. Now what we are talking about here is a temperature controlled room where both the slips and the gauge being checked were placed in a ultrasonic vapor degreaser filled with freon 13 and then wiped clean with a disposable cloth. now if there was any oil left on either component after that it was so insignificant to even guess.

After use they were wiped with an oily rag to remove any human skin acid and placed back in the box for storage.

I agree with Andrew about his thoughts on Nitrogen getting between the blocks without an oil film but wring two of these blocks together and try pulling them apart, With master blocks you will not succeed.

Also optical flats which are used to check the blocks do not have any oil film on them and you have to ware special gloves to handle them. they are made of special optical glass or quarts crystal. place them on the surface being checked and switch on the sodium light and you will see black rings where there is any ware.

But to get to the point the amount of oil on the surface would be so insignificant it is really not worth talking about. Now don't forget temperature plays a big part and I dought if you will ever use or see gauge blocks outside a Met room.

Larry

Edited By Larry Coleman 1 on 09/01/2015 09:54:40

[MuzzerParticipant @muzzer]

At the risk of collectively losing the will to live, IIRC the Van Der Waals forces can be sufficient to provide significant cohesive forces between (sufficiently) smooth parallel faces. In the extreme it is possible to join surfaces of similar material without the need for adhesives. The force is inversely proportional to the cube of the distance and obviously also proportional to the area. The "weak" VdW forces are more long range than the direct interatomic forces holding the atoms together.

Microscopically, the surfaces of even the finest pair of gauge blocks will be fairly rough but with enough surfaces in close proximity to generate some degree of VdW pressure. There is clearly some gap size at which they begin to come into effect and it looks as if the very fine end of the gauge block quality range (master blocks?) may be in that zone. The effective gap will be a function of the surface roughness and the residual crap (oil etc) left on the surfaces. Of course, if the surfaces are not almost perfectly clean, there will be surface tension and other effects resisting the wringing movement as a result of oil and contaminants.

Sitting in my armchair with my flak jacket on…

[Jerry WrayParticipant @jerrywray14030]

Oh No! Not van de Waals forces! There has been much correspondence amongst physicist disputing the existence of these. Perhaps we should all back-off until we have read the latest research papers, Then we might be able to take a view.

For the uninitiated these forces have been in dispute for at least forty years.

Jerry

[MuzzerParticipant @muzzer]

You'd better write to all the schools and universities around the world to let them know then, as it's been taught for many decades – and continues to be. When in Rome…

Merry

[Jerry WrayParticipant @jerrywray14030]

I bow to your greater knowledge.

Jerry

[Jerry WrayParticipant @jerrywray14030]

I bow to your greater knowledge.

Jerry

[Neil WyattModerator @neilwyatt]

> van de Waals force

Eye Level?

[jason udallParticipant @jasonudall57142]

Lets tryagain

[jason udallParticipant @jasonudall57142]

[Author]

Posts