Articulating options for coupling rods

[97xx]

I have a set of double-layer etched N/S rods for a 6-coupled loco to fabricate, in 00 gauge.  I will have one (rear) fixed driven axle and intend to compensate the front two with hornblocks and a wire and tube typical arrangement bearing on the axles.

 

Currently the rod etches are not cut into two rods (so you could solder them up as single solid rods if you had flangeless centres wheels).

 

Could someone advise me whether it is best to articulate:

1. By having a halved joint at the crankpin (and thus a 'dummy' rivet at the 'real' point of articulation), or,
2. Using the 'real' joint point as the articulation using a rivet?

 

Everything tells me to do 1 as this will be stronger if less truly prototypical.

 

However, I'm sure that this is a well-trodden path for the experts... Thanks!

[doilum]

Working in 7mm I have built kits with the second option but these tend to be a triple laminate. I might have concerns over the support for the joint with just two. When scratch building it is usually option one as it allows me to get away with just a double lamination or, better still, file the rods from a single piece of solid bar.

Edited November 9, 2020 by doilum
Additional information

[Rob Pulham]

I would suggest whichever method you choose that you make up a third lamination to support the joint from both sides. By coincidence I  have just done the  same exercise in 7mm with  three layers of etch. See the GCR Class 5A thread in this forum.

[Miss Prism]

Method 2 is theoretically better because the articulated joint can be made tighter than a normal running fit, whereas in method 1 movement of the one rod to another is subject to 2 running fits.

 

[5050]

I tend to articulate on the middle axle.  I think I did use the rivetted joint method once but found it so much of a faff I didn't bother again.  Not experienced any strength problems (in 4mm P4) but, if there is only one layer of metal available (ie a one piece solid rod), I make up another layer with NS strip or scrap kit etch, using the one piece rods as a jig for drilling holes and then cut into the required sections and solder layers together - making sure I solder the correct layers together!  I file to shape if necessary after all the bits are soldered together.

[Michael Edge]

Overlapping on the middle crankpin works fine - it was done often enough in full size practice after all. Making a separate knuckle joint adds an additional point where an error can occur. Three layers are better but two are sufficient.

[97xx]

Great, thank you.

 

Yes, good point re additional potential error with a knuckle - which usefully reminds me not to cut the rod etches until after I have used them on the chassis jig as axle spacing guides.

[MarkC]

Option 1 for me

[doilum]

54 minutes ago, 97xx said:

Great, thank you.

 

Yes, good point re additional potential error with a knuckle - which usefully reminds me not to cut the rod etches until after I have used them on the chassis jig as axle spacing guides.

Use the etch rods and a bit of scrap etch to make a datum rod. This gives you something to go back to if problems arise later. It is my starting point when scratch building.

[Miss Prism]

2 hours ago, 97xx said:

Yes, good point re additional potential error with a knuckle - which usefully reminds me not to cut the rod etches until after I have used them on the chassis jig as axle spacing guides.

 

It's an age-old argument between 'making rods fit the chassis' and 'making the chassis fit the rods'.

 

Much will depend on hornblock methodology. Or the absence of it.

 

 

[doilum]

3 hours ago, Miss Prism said:

 

It's an age-old argument between 'making rods fit the chassis' and 'making the chassis fit the rods'.

 

Much will depend on hornblock methodology. Or the absence of it.

 

 

Scratch building: definitely in the chassis fit the rods camp!