Slip gauges are small pieces of metal that are made to be a very precise thickness. They come in sets containing an assortment of sizes so that they can easily be placed together to make any required thickness. Sets are either imperial of metric.
Each slip gauge has a very highly polished finished. This has the strange property that any two surfaces can be “wrung” together and they will stick together. This is done by cleaning the two surfaces. They are put together to form a cross. They are pressed together and then twisted so they are both in line. Any number of slips can be wrung together.
A set of slip gauges can be of different grades of accuracy. But any set will probably be good enough for a model engineer. Their usefulness will be more dependent upon their condition.
Fig. Set of slip gauges 467
Any measuring tool is never perfectly the supposed value it is meant to be – there is always some error however small. The problem when adding slip gauges is that the errors all add up. Of course some error are negative whilst others are positive. But to be sure that the overall length is within the acceptable range it means that the individual error of each slip gauge has to be exceedingly small. This means that slip gauges are individually, easily the most accurate standard of length in the workshop.
Slip gauges come in sets made to certain standards. It is likely that the lowest grade ie “workshop” is quite accurate enough for any home workshop.
Slip gauge accessories
Slip gauges are sold in sets. A whole set fits into a single box. however it is possible to get a set of accessories that are designed to be used with a set of slip gauges.
The main item in such a set are holders. These are designed to hold a group of slip gauges that have been wrung together. For convenience holders are provided to hold up to 1inch or 25mm of slip gauges, then from 1 to 2 inches of slip gauges etc. There are also parts which have pieces that project out when held. These are semicircular. When measuring the radius of these together have to be added to the thickness of the slips in the holder. Consequently a set will be either metric or imperial.
fig set of slip gauge accessories
Fig. slip gauge holder 699
In this case there are two ends on the outside and two slips in the middle. These ends have very accurate semicircular bits that stick out. The radius of the ones in the picture is 2mm. The inside distance is that of the slips. The outside distance is the same plus 4mm.
On a well used set the ability of the slip gauges to wring together can be limited. A holder can be useful in such a case.