The cube and plate is a very challenging - some would say notorious - training exercise used in the engineering industry. The two parts have to be made predominantly by hand filing, without the aid of machinery, and must fit perfectly together. Another internationally famous firm has used it as a "passing out" test, but at RSAF it was, for many years, the introductory exercise used to teach apprentices the art of filing, handwork and basic metrology (the science of precision engineering measurement). A high degree of hand/eye co-ordination is essential and the skills are much the same as those required by "Gun Lock Filers" prior to the introduction of the "interchangeable" methods of production in 1857.

The cube starts as a rough lump, sawn off a piece of `black' steel bar, that is, just as it comes from the rolling mill.

The first stage is to file one face perfectly flat and test it against a "surface plate", a high precision flat surface. Then the second face has to be filed both flat and accurately square with the first. The complexity and difficulty of the task increases as each face of the cube is produced in turn and all six must eventually be perfectly flat, precisely square with all the adjacent ones and exactly the same size to within a few ten thousandths of an inch in all three directions, all over each pair of faces. If you did not achieve the very exacting standard demanded, you were made to start again!

The plate started likewise, rough cut from a piece of `black' steel plate. A surface grinder (for some the first introduction to machine tools) was used to grind the two faces perfectly flat - then it was handwork again. The outside edges were filed similarly to the cube. The central hole was marked out using precision instruments, cut out roughly by drilling four rows of holes and chiselling, then finished by hand filing to the same high standards of accuracy as the cube. The cube had to fit exactly in the hole every possible way round.

The "gold standard" was that only blue light should be visible between the plate and cube, indicative of a fit closer than "half a thou" (0.0005" or 0.012mm.). In practice that was almost impossible to achieve in every orientation, but some would achieve it in some of the many ways the cube and plate can be assembled together and most would get it to within about "a thou" - one thousandth of an inch (0.025mm.) all round.

We do not have one of the originals but, in 2006, former RSAF apprentice Ken Dee has made the cube and plate now displayed in the Interpretation Centre on the former RSAF site, using the authentic methods. In fact, not having a surface grinder in his garden shed workshop, he had to do the plate as well as the cube entirely by hand filing That he can still do it, 57 years after he made his first one, in 1949, is a clear demonstration of how very well engineering skills were taught and learned at RSAF!