Jack, gauge blocks are extremely accurate and certified components made from high grade tool steel or ceramic. They are normally used as a means of setting or checking measuring equipment. For example they will allow you to check a micrometer, or even set the postion of a DTI in a height gauge etc.

Google is your friend incidentally.

Gauge blocks can also be 'wrung' together to create lengths not available as a single block. This can be useful for setting sine bars, or for calibrating, or checking, specific dimensions. It is important that the gauge blocks have a very thin coating of oil before they are wrung together. See this thread on 'practicalmachinist' which also includes links to some manufacturers notes:

**LINK**

Regards,

Andrew

Andrew,

Thanks for posting that link …

The NIST "Handbook" linked within that thread is a valuable reference.

[also available via the Wikipedia page on Johannson]

MichaelG.

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For the sake of completeness … here is the NIST page

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Edited By Michael Gilligan on 30/10/2014 08:33:27

Edited By Michael Gilligan on 30/10/2014 08:35:31

Edited By Michael Gilligan on 30/10/2014 08:48:08

If you search on Ebay for "slip gauges" you will usually find second hand sets for about £40.They can be made from ceramic or tungsten carbide as well as the usual hardened steel. The big advantage of the carbide or ceramic sets is that these do not go rusty. Sizes can be from 0.020" to 4" on the imperial sets. Normal sets start from 0.100".

The usual sectional size is about 9mm x 35mm but gauges blocks can be square (made by "Precise" ).

Slip gauge prices have reduced a lot over the years. I remember the early sets were over a £1000.

Length standards have not changed much over the last 70 years and slip gauges are still widely used as the reference standard.

A set of slips will last a few lifetimes and will not depreciate in value if they are not abused.

Edited By Dinosaur Engineer on 30/10/2014 13:42:04

Edited By Dinosaur Engineer on 30/10/2014 13:42:35

Edited By Dinosaur Engineer on 30/10/2014 13:44:06

Edited By Neil Wyatt on 30/10/2014 16:38:08

Dino,

Put a space between a quote and a closing bracket.

Neil

Michael is right – slips should be "wrung" together without oil for the reason he gives.

Rik

As explained above Gauge blocks / slips are used to measure to very precise dimensions. In a full set of imperial there are normally 81 blocks plus two protective slips and in a metric set there are usually 88 blocks + two. I have seen and actually own sets with larger numbers of blocks however with a standard set you can combine blocks together to make any size going up in .0001 imperial or .001 (or finer) in metric up to the capacity of the full set. Normally there are standard sizes 1" 2" etc or 25mm 50 mm then there are increments of smaller amounts .1 .2 etc then even smaller units .01.02 etc. So by using the correct combination any size can be wrung together. When a good undamaged slip is wrung to its neighbour due to the lapped surface finish the slips "stick" together and can only be parted by using a twisting motion NO OIL should be used. Immediately the slips are finished with they must be separated. If left for a long period it will be found that they cannot be parted without considerable damage rendering the blocks useless.

A type of gauge block was first developed by Joseph Whitworth of screw thread fame when he was standardising the inch measurement using them he developed a micrometer measuring to 1 millionth of an inch accuracy. The Government of the day showed no interest in these and they were ignored for years. However on the outbreak of the first world war it quickly became apparent that an easily transported system of gauges were needed in order to produce weapons, shells, bullets etc. in factories all over the country to a standard size so that they fitted together. So the government imported a large number of sets from Johannson in Scandinavia hence the name joey blocks sometimes used by the more mature engineers.

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

Andrew,

I was always told to ensure that the surfaces of the slips were clean i.e., free from grease, oil and finger marks before wringing the slips. I can understand them being oiled when they are returned to the box. I think the main idea was to ensure that there was nothing between the slips to ensure accuracy. In addition, the slips do not need oil or any other lubrication to wring.

Interesting.

PhilH

It may be chapter and verse, but possibly from the wrong songsheet.

The quotation above relates to the preparation and cleaning of gauge blocks for comparative calibration using an electro-mechanical comparator with LVDTs. In the comparison process individual gauge blocks are compared with a block of known length. Wringing is not mentioned, or used in the comparison process.

Appendix B in the link given makes for interesting reading. The tentative conclusion is the wringing force is due to a liquid layer. And the thickness of this layer is accounted for in the calibration of the block.

Regards,

Andrew

LVDT = linear variable differential transformer – a pretty nifty linear displacement sensor capable of resolving down to nanometres, although I used them on the more prosaic task of measuring suspension ride height on racing cars.