Slip gauges

[Jed MartensParticipant @jedmartens56976]

Thanks chaps, that's an impressive collection of advice in just 24 hours.

I appreciate the arguments for and against buying second hand, and I have no doubt that there are bargains to be had. But I don't have the experience to judge the quality of a second hand slip gauge, and given their role as a reference, I want to have confidence in them.

The gauge holders look interesting, and I can see how they would be useful. The holder itself appears simple to make, but am I correct in thinking that the jaws (placed either side of the gauge block stack) need to be of similar accuracy to the blocks?

Based upon the above advice, my feeling is that this 47 piece set will be more than adequate for my needs – cheaper than the ones I listed originally, and just the 5 micron block below 0.01mm accuracy.

47 piece set

Again, many thanks for all the input.

Jed

[not done it yetParticipant @notdoneityet]

My view is that while a single slip gauge should be within the tolerance one can work too, umpteen together have a cumulative error, so the stack may be different to a single slip of that thickness.

Obviously one uses the minimum number of slips for any particular thickness, but one or two missing slips in the set can increase the number required, thus increasing the total error. Even with errors like that, temperature and any other faults, mine are better than I can (generally) manage – or need.

My set is imperial, old and includes a mix of more than a single name (although by the same manufacturer). Still more than good enough for me! Not yet used them for more than checking my other measuring kit, so far.

To be honest, I think think they are a necessity for a machinist doing work for third parties, but for most ‘internal’ work for ‘one offs’ us hobbyists undertake, making the parts to fit each other is as easy as, or easier than, making the individual parts to a tight size specification.

An example is using the key, as a check for slot width being as good as using a slip gauge. The important part, for us, is to ensure both key slots (internal and external) are the same. Even making a stepped key might be good enough for us non-perfectionists – but not for someone buying in parts from several sources, and expecting them to fit with minimum fettling, would be unacceptable.

[Tony Pratt 1Participant @tonypratt1]

Posted by Phil H1 on 15/12/2019 09:32:51:

I am finding it quite difficult to think of a model engineering or home hobby application that would require slip gauges but they are really nice if you happen to have a set.

My slips are a collection of carefully deburred, bright mild steel off cuts that I also use for packing the milling machine vice. My precision surface plate is a piece of worktop protector (granite I think) from Wilkos.

Phil H

Most engineered components will only work with some degree of precision/tolerance/interchangeability, if you are happy to work as you do fair enough but other engineers will see the value of & use slip gauges.

Tony

[Enough!Participant @enough]

Posted by Phil H1 on 15/12/2019 09:32:51:

I am finding it quite difficult to think of a model engineering or home hobby application that would require slip gauges but they are really nice if you happen to have a set.

I guess you don't have a sine-bar either?

[Neil WyattModerator @neilwyatt]

Posted by Martin Thomson on 14/12/2019 23:05:19:

My top three bits of advice for metrology, would be:

Never trust a single measurment.

Think about temperature.

You're probably reading it wrong, check it with another tool.

Welcome to the forum Martin, a very useful first post.

Neil

[Howard LewisParticipant @howardlewis46836]

I have a set of slips, rejected from work as too worn even for shopfloor use. Now. not all will wring together.

I still take care of them, since they are probably still of greater precision than the instruments normally used for measurement in my shop. For most of the time they live in a lobby, inside the house, and are only taken into the workshop when needed.

The 0.1 Protective slips are always used at each end of the pack, to avoid wear on the other slips.

Since they started life with accuracy within a millionth of an inch, they suffice for my work in an environment that is not closely temperature controlled, and most certainly not humidity controlled.

Howard

[Robert Atkinson 2Participant @robertatkinson2]

Be careful, metrology can be addictive. I have caught it for electronics (81/2 and 71/2 digit voltmeters, Kelvin Varley dividers Atomic and GPS frequency standars and high resolution counters, Various precesion standards).
Fortunatly have not caught it for physical measurments but used to work with XYZ "robots" with 1 micron (0.001mm) resolution. Those needed thermal compensation. We (well me mostly) used a Rennishaw ML10 laser interferometer to confirm their performance. I do have a small surface plate and a old set of slips though. Nothing wrong with using them for setting up, marking out etc as long as you don't fool yourself as to the accuracy you are acheiving. Everyone should have at least a couple to verify other devices like micrometers and verniers. They don't have to be perfect, if you look after them they will be effectively constant and will allow comparative checks. If your micrometer said it was 14.98mm for years and now reads 14.80 it's likey your mic is wrong if you have 2 slips and the mic says they are both wrong, its 99.99% sure to be the micrometer (unless you have sat rubbing the slips together or warmed them up).

Robert G8RPI.

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