Slip gauges

Definitely in the 'nice to have' pile. I haven't got one, but I'm regularly tempted to replace my random collection of 'parallels' (things like ball race outers and bits of ground stock) with a set of proper parallels. Some past-it slip gauges for £30 would eb a great alternative for my agricultural engineering...

Neil

Maybe I can give some useful advice here... Whilst I play at making models in my own workshop, my real life job includes proper high precision metrology. I wish I could make stuff even close to the accuracy I can measure, but well, maybe one day...

Whilst you don't need slip gauges/gauge blocks for everyday work, with some knowledge they can be very useful. I wouldn't be without my sets. Even simple stuff like using a slip to offset a part from a stop is so useful.

You can build some very useful tools out of blocks. Simple stuff like ringing several block together is obvious, but added abother one on either end gives you a go gauge. Adding a 5 micron block gives you a no-go gauge.

I gnerally wouldn't recommend trying for micron accuracy as you'll never get that level of accuracy in the home shop. 10 micron (0.01mm) accuracy is already fooling yourself to be honest. Cheaper sets that don't claim higher accuracy are fine, then maybe add a couple of 5 micron blocks ( they'll be 1.005 actually).

I have several scary expensive sets of ceramic gauge blocks with sub micron accuracy - they live in a temperature controlled metrology lab. Simply touching them ruins the measurment for a few hours. Seriously, temperature is such an issue, I can tell if someone is just standing near to surface plate. If you're trying for micron accuracy outside of a temperature controlled environment you are wasting your time.

You can buy sets for holding blocks as shown by someone else above. They're great if you can find them but usually they're ridiculuously expensive and actually you can make them yourself as they don't need to be super accurate. The real accuracy is given by the blocks you use. One day maybe I'll get a nice antique set on ebay...

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.

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

I have aquired a lot of equipment over the years,including a good calbrated set of slip gauges,(at no cost) very occasionally used for measuring piston ring grooves on my stationary engines,I certainly would not buy a set,for a lot of work a set of Hoffman rollers in conjunction with a good little used set of feeler gauges is more than adequate for home measurement. Hoffman bearing co used to sell sets of very accurate hardened rollers,occasionally the s/h tool dealers have a set for sale,Slips should only be used on toolmaking work or inspection ,mainly in toolmaking where the parts are hardened and ground or setting up say a sine bar to measure precise angles. too much use on say rougher surfaces eg milled will cause wear on the slips.The measuring surfaces on slips should never be touched to avoid finger marking ,pick them up by the edges,if used to control stops on machine tools the narrow wear slips should be used on each end of the pile of slips though one is wasting time and effort and fooling oneself as most mill stops are not very accurate ,except perhaps when using a very good continental Deckel type mill.

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

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.

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

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

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

Neil

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

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.