A Pair Of Quick Change Gearboxes

John Crammond Recounts Making and Fitting a Pair of Home-made gearboxes

Many years ago, I was struggling through a rather uncertain period and worried that I might have to part with my faithful old Myford Super 7 that I’d bought secondhand in 1970. Presented with the possibility of being lathe-less I decided to make a machine of my own, and over the next few months patterns were made for all the major components and cast in iron at Birchenlee Foundry in Colne Lancs. At that time, this was run by a wonderful gentleman called Mr Slinger who I was horrified to learn some years later had lost his life in a road accident. I’m not sure whether the Foundry is still operating, but I always feel a tinge of saddness that of the thousands that once were the cornerstone of our Industrial Revolution, only a tiny handful still remain.

To cut a long story short the lathe was finished and as the mandrel ran in the time-honoured configuration of large twin opposed Timken rollers at the front and equally robust ball races at the rear, rigidity and hence performance was excellent. Ironically my circumstances improved and the threat of losing my Myford evaporated. My home made lathe continued to perform impressively as a backup machine when I came across an article on Quick change gearboxes, written by Mr Alan Buttolph appearing in the winter 1990/91 MEW. In it he describes the construction of a box predominantly based on the Sparey plans that may possibly still be available from MAP (I believe plans and castings for a development of the Sparey design, the ‘Machin’ gearbox, are available from Hemingway). Like Mr Buttolph I too had considered the Sparey box but had discounted it because of its bulky size. However Alan had persevered and redesigned the whole using 28dp gearing in place of the 20dp ones. This effectively shrunk the dimensions to 6” long by 4.5” wide and high, resulting in a very compact box of similar size to Myford’s own.