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coupling rods and crankpins in gauge O live steam

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Chris Kaminski29/06/2021 13:37:12
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In bigger gauges coupling rods are bronze bushed and run on steel crankpins.

Wear (when it happens) is to the bushes, which can be easily re-bushed when needed.

In gauge O there is no space for bushes.

LBSC makes coupling rods from "steel strip" and says:

"...There is no need to bother about bushing such weeny rods for the first kick-off....If in the course of time they should wear and begin to rattle, they can easily be taken off, drilled out and bushed with a scrap of bronze in a few minutes..."

Evans suggests that crankpin holes in the coupling rod should be case hardened (with silver steel crankpins).

Eddie Cooke says:

"...I case-harden as the fitting of bushes would require a large hole to be drilled, which would leave very little metal round it. Hardened eyes will outlast umpteen bushes and are easier to make..."

Clarry Edwards, similarly says:

"...Crankpins are silver steel and coupling rods filed from 3/32" mild steel... the ends sre case hardened..."

So in summary the recommendation seem to be:

silver steel crankpins, mild steel coupling rods (no bushes) with case hardened ends

My question is about wear of such a combination?

Will the cranpins wear before coupling rods?

Would it be better to harden crankpins as well?

I realise that majority here will have experience of bigger gauges, but it's worth asking the question...

IanT29/06/2021 15:05:31
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I don't build in '0' Gauge Chris - but assuming the coupling rods are fairly simple in nature, I'd tend to go for silver steel (hardened) crankpins and 'soft' coupling rods.

The reason being that it will probably be easier to remove (and repair) the coupling rods (if indeed they do wear!) than remove and replace the crankpins. I wouldn't 'bush' them as such either. I think I'd try just brazing over the worn hole, filing it down flat and then re-drilling it back to the original size (easy if you keep & use the original drilling jig).

So, personally I'm with LBSC on this particular one - but I'm sure the G0 'Gurus' must have known what they were talking about too. In the end, you'll just have to take your pick!

Regards,

IanT

br29/06/2021 15:20:08
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As Ian T on this one, and this was the norm on Hornby, Bassett- Lowke. Bowman, etc on the majority of their 0 gauge engines. My current ACE locos are not bushed.

The higher priced models had bushes and sorry to disagree but there is space to fit bushes in 0 gauge - it just invoves some afine machining.

bill.

Chris Kaminski29/06/2021 16:04:31
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Posted by IanT on 29/06/2021 15:05:31:

....I'd tend to go for silver steel (hardened) crankpins and 'soft' coupling rods...

thank you @IanT

I am not questioning "Gurus" wink - just trying to understand reasoning ...

Like yourself, my thinking is that coupling rods would be easier to replace/re-bush than replacing crankpins,

Hence my question.

Of course LBSC is not really a good recommendation - his designs (especially in smaller scales)

whilst practical, were overscale, oversize, over loading gauge and would not be acceptable today (things have moved on since his days...).

On the other hand, chaps like Clarry Edwards or Eddie Cooke have great record of building many beautiful live steam models in gauge O, so I do not doubt their expertise... just trying to understand how does it work.

Chris Kaminski29/06/2021 16:11:14
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Posted by br on 29/06/2021 15:20:08
...

thank you @ br

Like I said in my reply to IanT, things have moved on since the days of Basset-Lowke and Bowman.

ACE locos are electric? not live steam? (unless I am missing something) so not really like for like comparison to what I am talking about?

Yes, you are right bushes are possible.

The main argument against them in live steam model is the one Eddie Cooke offers:

"...Hardened eyes will outlast umpteen bushes ..."

Now, I guess he is right (I do not doubt his experience and expertise), but I am querrying the effect of case hardened coupling rod eyes on soft crankpins?

br29/06/2021 17:22:55
697 forum posts
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It matters not wether steam or electric, the motion is the same for both . You are splitting hairs, as not part of your original question.

Also have things moved on since BP and Bowman? The motion , which is your original question, is the same engineering and principles as it was 50 years ago.

Hardened eyes will outlast umpteen bushes is spot on.No guesiing involved.

bill

PS you are correct in saying ACE trains are electric , so you are not missing something.

I have hornby and bowman without bushes, some are 70 yeasrs old from my youth, still original and no signs of wear. I could not say if the rods are case hardened .  I suspect the operators such as ourselves will wear out before the engines . wink

Edited By br on 29/06/2021 17:23:38

Edited By br on 29/06/2021 17:45:06

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