In my last article about how I made a safety valve bonnet, I mentioned that I was given the challenge on the basis that I had done some spinning but that I could not use this process because the cover was not round. Well, I have since been made aware that not all members are familiar with the process of spinning and it was suggested that I might like to pen a few words on the subject.

Spinning is a forming process which can replace beating or pressing. It is the shaping, in a lathe, of a disc of metal over a relatively cheap former, known as a ‘chuck’, by means of pressure applied with a hand held tool. Owing to the large forces needed, the tools are held on a rest with a number of holes in it. A peg can be dropped into these holes to form a pivot point against which the tool can be rested. The tools themselves are some 34” long in order to obtain the necessary leverage without tiring the arms. The chuck is turned from hardwood and the blank is held firmly against it by a backing plate pushed up with the tailstock. The blank needs to be annealed and, depending on the depth of the spinning, re-annealed at intervals to prevent ripples and cracks from developing.

My first challenge in the process of learning how to spin metal was to obtain some tools. This proved impossible so I made them up myself using handles turned from ash with ½” dia. silver steel ends inserted (Figs.1 & 2). These were polished and suitably hardened. Steel tools are used for non-ferrous work and bronze tools for steel. I then made up a revolving centre for the tailstock with interchangeable back plates. Spinning is carried out at high speeds and I was concerned about the blanks being thrown out so most of my back plates have a central spigot to prevent it. So far so good. Then it was the moment of truth. I turned up some simple chucks, cut some brass blanks and just had a go.

Then it was the moment of truth. I turned up some simple chucks, cut some brass blanks and just had a go. I achieved enough success that I am now happy to have a go at anything I can fit into the lathe. I have since made up an egg-cup for a present, stainless steel cylinder covers for a 7 1/4” Gauge A3, a brass sump for the fuel tank on our lorry and also the fuel tank ends. These were 15” diameter and 16SWG steel and were done on a Colchester. I attempted those with some trepidation but they were fine in the end.

I think the best way to explain this process is with a series of pictures so I show here a sequence taken during the making of an end plate for a cylindrical fuel filter. The finished diameter is 3 ½” and the depth ¾”. Fig.3 shows the annealed blank held against the chuck with the back plate. The back plate is supported with a taper roller bearing but for only occasional use, a normal lathe centre will do. Fig.4 shows the blank being lubricated with a bar of soap being held against it while it rotates. This is used because the spinning process is high speed (1000prm in this case) and any lubricant tends to be thrown off. The soap sticks quite well but does need to be reapplied at intervals
		Figure 5 shows the tool being applied to the job. I usually start with the first push working from the centre outwards to bed the blank onto the chuck. The next push is from the edge inwards. This helps to maintain the plate thickness. If all sweeps of the tool are outwards then the material tends to thin. After two or three sweeps pushing the metal a little bit each time, annealing is required. After a couple of annealings, you end up with Fig 6 where the brass is beginning to lay down nicely.
		Fig.7 shows it in the finished position ready for parting off. Care must be taken not to push the brass down too hard or you will end up drilling the chuck out of the back! After parting off (Fig.8) and a little bit of attention with a piece of emery, you end up with Fig.9.
Quite complicated shapes are possible with this process, particularly if chucks are used which are multi-part. I have only been able to give a very small taste of the process here. However, for those interested, may I recommend the excellent book, ‘Metal Spinning’ by Reagan and Smith available from Camden Books. This gives a much more detailed explanation and warns of some of the pitfalls with explanations of how to get out of trouble. It also makes the somewhat disconcerting statement that you can tell how long a spinner has been working by looking to see how many fingers he has left so should you decide to have a go, be careful!
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