BMS , Bright Mild Steel or BDMS (as it used to be called, the D standing for Drawn) is sized by passing it through a die that induces stress in the outer surface. Machining one side will tend to unbalance the stress forces, resulting in distortion. My assumption is that silver steel is manufactured by annealing ( to make sure it is in the soft state) and then grinding whereas, presumably, PGMS is just ground enough to bring it to size (can anyone confirm?)

If you are prepared to machine the whole surface yourself then black bar should be distortion free.  BMS is usually a thou or two under the nominal size.

HTH

Rod

Edited By Roderick Jenkins on 24/08/2015 12:40:21

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John,

That's an E.W. Cowell [of Watford] tailstock adaptation, and they were supplied soft.

… I bought mine, new, from N. Mole & Co. [a.k.a Amolco]

MichaelG.

Roderick Jenkins and Michael Gilligan:

Thank you both for your helpful comments. I recall the lobate silver steel point from some years ago, the problem being that the out of roundness could not readily be detected by a micrometer; rolling the bar on a flat surface would give an indication, however.

A quick google suggests that some "precision" ground bar is indeed centreless ground and I notice that the manufacturers of silver steel emphasise the precision of their product so I think the point about the grinding method is unresolved. My impression is that industry would want to use the quickest and cheapest method. I did see references to the annealing of silver steel.

I like the black bar suggestion although I think that I would have difficulty in buying a short length and therefore I will probably go for silver steel and try to obtain an assurance about its roundness.

I feel I have to point something out. Centreless grinding is used rather a lot for 2 reasons. It's convenient and in terms of roundness tolerance and repeatability more precise than between centre work. It can also be arranged to work up to shoulders and to produce tapers. Convenient largely relates to the ability to easily hand long lengths.

On the other hand if people want to believe otherwise that's fine by me. I just happen to know why it is sometimes favoured for mass production work. A similar idea is used in other areas as well.

John

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That's very classy, John

MichaelG.

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That link supports what i say, they can achieve better tolerances on cylindrical grinding than on centreless and remember that these are best tolerances and you will pay dear for them.

However this thread is degenerating, as usual, into the realms of theory.

As regards the OP then a length of silver steel will be more than good enough for the project IF it is available in the size required. One example is the Super 7 which has a barrel size all of it's own.

I did go back and read the original article and saw no note about lobed material, material moving under stress and I dare say that if you peruse the post bag press of the day, none of these items would have been mentioned.

I wonder why that was ? Was it because people just got on with things [ probably judging by the articles of the day ] or writing a letter was too much trouble whereas penning a reply via the t'internet is far easier.

John Stevenson:

I have had a Myford lever feed in amateur use for several years and much prefer it to the standard screw feed. My lever needed overhauling to remove play in the bearings and I have also fitted it with an improved, longer handle with more comfortable grip. The positive experience with the Myford was one reason for wanting to modfiy my larger lathe and I did think about a scaled up lever feed but felt it would be unsatisfactory partly because I couldn't see how to design a linkage that would give me the length of barrel movement that I want. I shall not be emulating the superb Cazeneuve although I do plan to incorporate the capstan within the body of the tailstock rather than hang it off the end.

Good point about the Super Seven barrel: mine is 1.115" diameter which is certainly not a standard size for silver steel. I have ordered a length of 1.5" material for my project and the supplier assures me it will be round and that I may return it if proves otherwise.

Can you tell us how your combined screw and lever feeds contrive to co-exist?

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If I need to apologise for mentioning that Silver Steel can (occasionally) be slightly lobate, then here goes:

… SORRY …

It was just a passing comment; I wasn't trying to start WWIII.

MichaelG.

I have some PGMS I bought from Reeves when they were in Marston Green. I'd say without doubt it was centreless ground. There is still a bit kicking about, a little rusty now. Size was accurate but I feel the finish wasn't as good as it could be.

There was also a company that bought in really precision ground silver steel even better than what Stubbs used to produce and that was also centreless ground and unusually straight. They did this in a few sizes mostly in the smaller sizes up to 1/2in for one of their customers – they also sold off cuts of everything at 10% over scrap ;-( then got bought out and all of the offcuts were binned. They just loved telling model engineers that.

No need to apologise Michael. I just mentioned that area because it's one that people sometimes get carried away with. No WWII as far as I am concerned. Don't start worrying about straightness.

John

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I've never seen any like that Rod. My stock was bought from a place that was disposing of it and it's all nice and smooth and shiny and no markings at all. The PGMS I mentioned had a wide very coarse spiral running along it. Visible rather than measurable really. I think they mostly sold it for use on pulley spindles. Sadly missed as they sold a lot of very useful stuff. From memory they sold PGMS in their usual 3ft lengths.

A little while ago I bought some of the precision ground bar that is sold for use on CNC machines. I understand it's more of a tool steel and is also heat treated. I wanted it to replace the spindle on my boxford's countershaft as I fitted new bearings and expected it to be very accurate but it was more undersized than I expected. Not bad to machine. It's been on and off the machine, currently off. I have a bit of a pulley problem. I couldn't help making it longer than needed – over head drive but suspect that will have too many other problems really.

I do have an odd sort of interest in centreless grinding. My father was a large company's metal removal expert. He watched my growing collection of tooling at home with interest. During the WWII he was a toolmaker and talking one day about the problems of hardening and grinding at home he said why not make yourself a centreless grinder. It seemed they were allowed a lot of freedom in the ways and means department during the war as there was more interest in getting jobs done – they had even been made some out of wood. The DTI used to borrow him to help sort other companies problems out – when they were actually interested in keeping UK manufacture going.

John

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