Material for coupling rods

[Joe McKeanParticipant @joemckean81940]

I'm about to place a order for some materials and was wondering if there was a preference on what grade of steel to use for the coupling rods on a 3.5 gauge steam locomotive.

I was going to order BMS (080A15) but thought I would check to make sure.

Joe

[Joe McKeanParticipant @joemckean81940]

[Nigel Graham 2Participant @nigelgraham2]

No special preferences for the connecting and coupling-rods on a model locomotive, and they normally are made from mild-steel.

I think most builders do use BMS but remember it can distort when machining along its length releases the stresses locked up in it.

No reason you could not use hot-rolled mild-steel to reduce that risk, other than perhaps it needing more cleaning up.

[Phil PParticipant @philp]

Or if you have an open hearth fire in your living room, you can chuck a few lengths of BDMS in before you go to bed and then leave it to cool slowly overnight and it should be nicely stress relieved in the morning.

Phil

[Nigel Graham 2Participant @nigelgraham2]

You may as well buy hot-rolled steel bar in the first place!

Stress-relieving BDMS like that won't guarantee it staying straight, but it should be fairly easy to straighten.

I did use the solid-fuel stove in my first home, for over-night annealing the differential gears for my steam-lorry's axle; using an ex-British Leyland front-wheel drive unit modified to suit.

[Phil H1Participant @philh196021]

Joe,

BMS worked perfectly fine for me but the coupling and connecting rods were for Rob Roy which is relatively short.

I experienced absolutely no distortion and no other problems. I used 1" x 1/4" bar which is a bit wasteful but it allowed me to get some nice clean 1/2" diameter 'corners' to start the profile and allowed me to grip the bar in my vice during the chain drilling process all along the edges. However, it still took ages to clean up the edges on my small Chester milling machine.

Phil H

[Nigel McBurney 1Participant @nigelmcburney1]

I would use round bar, far more choice of material,virtually no distortion,leaded mild steel gives excellent finish,I have made con rods for full size stationary engines from en 1 A leaded and got execellent results and finish.I remember an ME article back in the 1970/80s where a top class modeller liked stainless coupling/con rods and othe valve gear for 5 inch locos and made them all from round free cutting stainless bar.OK it requires more machining at the roughing out stage but it worth it.I used carbide tips which have chipbreakers for the roughing out this avoids lots of strings of swarf,then finish off with HSS tools.

[KWILParticipant @kwil]

Ground flat stock aka guage plate is good starter?

[Nigel Graham 2Participant @nigelgraham2]

Gauge-plate? No, no at all for the connecting-rods. It is hard stuff to machine, and gives no functional advantages there.

Use it for the guide-bars maybe, and it is a common choice for the expansion-links; but not for anything else.

Leaded free-cutting round bar – yes, and I think a limited range of square sections is available, possibly easier and less swarf-generating for basically rectangular-section parts.

'

(I am using BMS for my wagon engine's guide-bars and eccentric-sheaves, with cast-iron crossheads and eccentrics; and may use the same respective combination for the expansion-links and die-blocks.)

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