Jointed Coupling Rods - Advice needed

[BetweenTheTunnels]

Evening all,

I am scratch-building a Gresley J50 0-6-0T .. my thoughts are turning to making the coupling rods, but as im using High Level Kits CSB to give some springing to the wheels, there is a need for the coupling rod to flex slightly (I think).  I am therefore assuming that like the original, the coupling rod needs to be made from two separate pieces so that they can have that +/- 0.5mm deflection if needed.

 

My query is how do people do this, and specifically how to join the two? I had thought of a nut behind the rear piece with a very small BA screw through to give a slight pivot point, but the nut will stop the wheel turning.  Any thoughts or advice would be welcome please - I have had a search through rmWeb, and although there are plenty of topics that include talk of coupling rods, none that I have looked at so far seem to answer my query.

 

Richie

[brossard]

Wizard models should have coupling rod sets that can be articulated.  I've done them myself with Comet chassis kits, but many, many many... years ago.

 

You could try these:

 

 

I've tried CSB and I wish you luck with that, I found it all to be a faff, but that's me.  I much prefer compensation which is easy and works well.  Iain Rice's Etched Brass Chassis Construction was my bible.  It's outdated now but still worth a read.  Copies can be found second hand, but you're not having mine.

 

John

Edited September 8, 2023 by brossard

[Grovenor]

Generally there are two main options,

1.  Make the joint on the centre crankpin with each rod half thickness at the crankpin, make the protoype joint just cosmetic.

2. Make the joint where the prototype does.

    a. If using two layer rods make a half joint as 1 above fixed with a pin soldered to the rear half or riveted.

    b. If using 3 layer rods solder a pin to the centre layer then fit front and back layers round it and solder the layers together.

Either 1 or 2 will work, experienced modellers tend to prefer 2. 2b makes a very nice joint if you can get appropriate etched rods.

Etched rods can be had from Alan Gibson, Bill Bedford, Lanarkshire Models and Supplies and no doubt others.

[Izzy]

This will probably be controversial but I long ago gave up pivoting coupling rods and now leave them solid. Indeed I solder up jointed ones in the main as those fitted to a lot of RTR are so poor they have a bad impact on running qualities, (I say this as the person who first designed the above universal rods that Gibson produce). The reasons are mainly because you don't actually need much play/movement to get differential axle movement, just making the rods a nice easy/loose fit on the crankpins is enough, and it's often difficult to keep jointed rods accurate, that they keep the same crankpin distance over a full wheel rotation. This can become a real pain if the drive is off an outer axle which is often needed with a model loco, having serious impact on running qualities per revolution. It can be achieved but frankly isn't worth the hassle.

 

Bob

[Brassey]

You can use a valve gear rivet instead of a pin.

[garethashenden]

Pivoting the rods on the crankpin is much easier and what I would recommend for the first time. Pivoting them on the prototype's joint is more accurate, but harder to set up and there's more risk on soldering everything solid. When you pivot them on the crankpin they can stat as two separate pieces. The wheelbase seems to be 7'3"+9'0", so Alan Gibson part 4M88 would be appropriate. You make no mention of scale and gauge, but the High Level parts suggest 4mm. 

[MikeTrice]

High Level Kits do a chassis for the J50 designed for CSB. Worth considering?

[brossard]

If you're working in 00 (or any gauge really I think), bear in mind your gearbox will have to get between the hornblocks on the driven axle.  I struggled with this even with reduced profile hornblocks.

 

John

[BetweenTheTunnels]

Hi Chaps,

Thanks for all the responses, and the various thoughts. Apologies I thought it was in my signature, but it doesnt seem to be showing.  Im scratch-building this in 3mm scale, so I think the Gibson rods and Wizard Models options will be overscale.  I think I might go with the suggestion made by @Izzy to start with and make a fixed coupling rod, and see what the movement and options are.   I did consider that but, having not done this before, I felt it might be a case of ruling out any benefit of CSB on the wheels. If that doesnt give the end result, I think my next step will be to go for a pivotted rod on the middle axle crankpin.  I can make the rods look as though there is a joint just before even if there isnt in reality.

 

The gearbox im looking to use will be the HLK one thats designed for 3mm - ive forgotten the name of it now, but doing the sums I think it should fit ok.  I was debaiting whether to have the gearbox drive to an intermediate gear, then separate gears on the middle and rear driving axles - a bit like the old ringfield assembly, but I concluded it was likely a lot of a hassle for very little (if any) gain.  Unless anyone can see any benefit Im missing?

 

Thanks to everyone for their thoughts/feedback so far

 

Richie

Edited September 9, 2023 by BetweenTheTunnels

[Nick Holliday]

As a 3mm modeller, you are probably aware of this company https://www.3smr.co.uk/locoscomponents.html . They do an etched chassis for the J50, including the coupling rods. From memory, I think they are rigid, but at around £7 each, a couple of them would provide you with enough parts to make a jointed set if the rigid approach fails, and also give you a generous collection of useful frame spacers of different sizes for other projects. (I think reduced at 75% from a 4mm etching)

[BetweenTheTunnels]

Hi Nick,

Thanks, yes I was aware of 3SMR and the etched chassis (although I hadnt thought of getting one or two for the rods!).  My whole ethos behind scratching building the J50 is to prove i can do it.  There are other locos I want to build and run, for which there isnt any kits or parts available, and they are more complicated than an 0-6-0T!  My reckoning being if I can scratch build this and get it to look right and run well, then i should be able to build on that knowledge going forward.  Famous last words and all that, but hey we've all got to start somewhere!