Crankpins?

[ron]

Hi Everybody
I've just finished turning a set of loco crankpins from silver steel, should these get hardened and tempered or left as they are?
Ron

[chris vine]

Hi Ron,

Some people say harden them, I think Tubal Cain used to say that it did not make any difference?

One thing to watch out for is if there are any holes which need drilling to locate a return crank for outside valve gear.

For what it is worth I hardened mine.

Chris.

[baggo]

hi Ron,

most of the construction articles I have read say to leave the silver steel unhardened to avoid making the crankpins brittle and liable to snap off (although I wouldn't have thought this would happen under 'normal' use). Silver steel left in its natural state is pretty tough stuff and should wear well. I did read an article by Keith Wilson in which he related the story of trying to straighten a hardened silver steel crankpin that was slightly out of square. He 'tapped' it with a hammer to straighten it and it snapped off like a carrot! After that episode he always left them unhardened.
Another article suggests avoiding the use of hard phosphor bronze for the connecting/coupling rod bushes with silver steel pins as the bronze can 'pick up' on the steel and cause scoring. The authors suggest using gunmetal bushes to avoid this. One of the softer leaded bronzes would also be suitable.

John

[John Lee]

Left as they are Ron,

If you harden them, you will be left with scale which will take your tolerances out, and it might well distort them as well. The George Thomas book "The Model Engineers Workshop Manual" has a chapter on this.

To save the investment.. in small diameters silver steel (or drill steel to our colonial friends) is hardened by the drawing down process by dies almost through and through.

John

[simonwass]

Although I've used silver steel for crankpins without trouble, I have been told not to use it as it isnt good in shear, which crankpins always are.
Simon.

[ivanj]

I have used stainless steel and brass bushes for what it is worth. Pump shafts are often made like this and they survive.

Ivan

[Shawki Shlemon]

Hi
For crank pins I use silver steel ,no hardening. I have used hardened silver steel ( quenched in oil ) as inner shafts for roller bearing's on a four wheel bum seat which has been used for 20 years without any problems .I am 90 kilos and there is 10 Lt of water tank under the seat .I have replaced worn wheels once but not bearings or shafts . One can do either using correct methods.