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Best material for a crankshaft?

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Mark Gould 114/01/2019 07:27:01
114 forum posts
64 photos


As the title says, we have reamed the main bearing of our steam engine and we are wondering what material to use for the crankshaft. As we have reamed it 13mm I am assuming we need a precision ground piece for the best fit? And where does one buy a piece?

What would be the best material to use? Tool steel? Silver steel?



JasonB14/01/2019 07:37:03
15743 forum posts
1646 photos
1 articles

Well Ideally you would have sourced the material first then made the hole to suit. I assume you are going for a built up crankshaft rather than cutting from solid.

12mm and 1/2" Precision Ground Mild Steel are readily available and would be fine for your No1 but as you have gone for 13mm Silver Steel (drill rod) would be the best option for a ground finish. Bright Mild Steel tends to be a little undersize so not ideal as you already have the holes otherwise they could have been bored to fit.

EDIT what is the bar in the last photo of the engine that you posted and what is the fit like?

Edited By JasonB on 14/01/2019 07:38:45

Iain Downs14/01/2019 07:39:10
478 forum posts
361 photos

I claim no particular knowledge in this matter, but I've recently built a crankshaft and crankcase (well nearly finished) and have used silver steel for the crankshaft.

I've used silver steel is that this appeared to the most consistently used material in the online and printed matter that I've come across.

The reasons behind this appear to be a combination of more hardness than most steels, but still being easy to work with (which tool steel would not be).

It's very easy to buy on eBay from a variety of vendors. The rods I bought were around 1 thou under nominal size and within microns of the actual size from end to end.

I'm sure people who know will jump in with better reasons (or probably alternatives), but that's my 2.5 penn'orth.


Mark Gould 114/01/2019 07:54:22
114 forum posts
64 photos

Jason, Iain,

That is a 13mm piece of what I thought was silver steel but turned out to be quite soft. I was under the impression that a crankshaft should be made of a hardened and ground material but my newbie status is on full display here, I simply don't know enough about the different metals yet or of their properties to make an educated decision.

I see your point on boring the holes only after getting the material. Almost as if I am going at this bass-ackwards.

Thanks again for the advice Jason and Iain, I will take a look on eBay too.


JasonB14/01/2019 08:01:18
15743 forum posts
1646 photos
1 articles

In the as bought state silver steel will not be a lot harder than plain mild steel so you may well have some.

For your No1 there is no need for exotic steels, hardening or ground surfaces.

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