As I said, I have come to the understanding that coupling rods that are jointed on a crank pin aren’t a good idea, and the way to go is to articulate them using a pivot adjacent to the centre crank pin boss. That’s the way they did it on the real thing, and the O4 came with articulated rods that proved easy to get running smoothly. Unfortunately as far as I am aware, the only assistance available for producing coupling rods for the J10, and hence avoiding a total scratch building job, is the Gibson universal coupling rods etch. This produces a reasonable looking set of rods, but they are jointed on the centre crank pin and are thus unacceptable. Previous experience also suggests that when assembled as intended, the results were a bit flimsy.
The question is, can one use the Gibson offering as a stepping stone to rods that are articulated as per the prototype and a bit more robust as well. The fact that I’m posting this should suggest that the answer to that question is probably, yes.This is the Gibson Fret
The thing about these “universal” coupling rods is that you normally start from an existing chassis, with the axle centres established, and build the rods to fit what you have. The rods are made from a two layer etch, and you can have plain or fluted depending on which way round you mount them. No part has more than one crank pin hole. Using the chassis plus some reduced end axles as a jig, you put a fluted and a plain part back to back to fit between the ends of one pair of axles, then solder them together, finally adding the boss ends to make up the thickness. When using this etch to make jointed rods, the process is rather different. I produced rods to measured axle centres and I shall be using the rods to set the axle centres on the chassis.
To articulate a coupling rod, the best way is to build a forked joint. To me this suggests a three layer construction. The Gibson etch provided the two outer layers, so all I needed to was make a central core from Nickel Silver (N/S) strip and, for the pivot, use a small valve gear rivet. The rivets are not obligatory, I had some in stock so I used them, but a couple of brass pins would have done the job. This drawing illustrates where I’m planning to go.
Firstly I found two strips of N/S wide and long enough to make the core layer of the new rods. They came from the edge of a N/S etch. I sweated these strips together, and carefully marked out a centre line, or more accurately an off centre line because the lubricators on the rods stick out further on the top edge. I then marked out the wheel centres along the rod centre line, drilled them 0.5mm, and opened out the hole to 0.95mm. I also fretted away some of the excess metal.
You will see from the picture of the etch that it contains a good representation of the articulation pivot points. I drilled through all these pivot points 0.5mm and all the crank pin holes 9.5mm. I used a combined crank pin/articulation pivot boss from the etched to establish and drill out the articulation pivot point on the rod core strips. Finally I cut part way through the core strips between the centre crank pin hole and the articulation pivot hole. The following picture shows one of the resulting embryo rod cores, once I had delaminated it from its twin.
As a matter of interest, all the metal pictured in this post is N/S, no matter what it looks like. The background to this picture was blue but this seems to have foxed my camera and I can’t be bothered to correct the colour balance!
Because I have recently got extravagant and splashed out on an Avonside Works Chassis Pro jig, I used these coupling rod cores to set up the axle centres on the jig. But fear not you can also set up the chassis from the finished rods in the traditional fashion.Getting the soldering iron out
Next we have to overlay the Gibson etch components on to the core. I used Carr’s 221 tin/silver solder, which I find runs well on N/S and gives a very clean finish. I had expected to change down to 188 or even 145 solders as I added details, but in practice I found it easy to do the whole job with the 221 stuff. Flux was Carr’s Red Label
The J10 rods are plain, so the fluted components will be fitted to the back of the rods. I began by fitting the plain overlays on the front of one end of the core, starting with the overlay with the articulation pivot point in it, and adding to it one of the separate end bosses. The overlay needs to be trimmed to the correct length. The bit I cut off is in the following photo.
You can see that, to get everything strait, I pinned all the bits together on my trusty wooden block. Once I was happy, I tack soldered the overlay in the centre, hence the unsightly splodge of solder there. The metal pin through the separate crank pin boss was removed and replaced by a wooden cocktail stick. That end of the rod, and about half way down the overlay, was soldered up neatly. Then I removed the other pins and finished the soldering job, making very sure I didn’t get any solder beyond the cut in the core between the centre crank pin hole and the pivot point. Then I re-drilled the crank pin holes from the core side through the new overlays. This makes sure that even if the overlay wasn’t aligned perfectly, the crank pin hole remains centred on the one in the core.
Then I turned the core over and put the overlays on the back. If you have a good look at the Gibson etch you will realize that the matching centre crank pin boss/articulation pivot point is attached to a fluted rod overlay at the articulation pivot end. This overlay will end up on the back of the other half of the connecting rod, so I had to separate the boss/articulation pivot point from the rest of the overlay. This boss is to be soldered to the end of the core I was working on, along with another fluted rod overlay with end boss attached. This also needed to be cut to length. Again pins through the crank pin holes and the pivot points ensured everything was lined up properly, before the overlay was tack soldered to the core in the middle. I replaced the pin through the centre crank pin hole with the cocktail stick and carefully soldered on the boss/pivot point, again not getting solder past the cut in the rod core. Finally I pulled out all the pins and soldered it all up neatly.
Once the soldering was done, I completed the cut through the rod core and pulled out the other end leaving a nice forked joint. I re-drilled the crank pin holes, from the front this time, again to ensure the crank pin hole will be in the right place. Finally I filed the core back to the outline of the overlays. After all that, I ended up with half a finished connecting rod as in the next picture, which also shows that the process of fitting the laminates to the second half has begun.
Cutting the overlay on the second half to the correct length needed care, but pinning it all down to the trusty block helped. I also learned that filing a concave end on the overlay by the articulation pivot point improved things, but only after taking this picture. I ensured the overlay was central on the core by aligning it with the articulation pivot hole. Before doing the others side, I filed the core back to the profile of the overlay for a short distance at the articulation pivot end. By doing this, I could line up the second overlay with the first without difficulty. The next picture shows this has been done, and there is the trusty cocktail stick in use. It should be vertical, but the hand that normally holds it upright is otherwise engaged in holding the camera, and, in turn the viewing angle of the camera is exaggerating the degree to which the stick is leaning. Diversion re the virtues of cocktails, or at least their sticks.
I’m a great believer in the use of wooden cocktail sticks when trying to align holes I want to keep open, in things I’m trying to solder together. E.g. when soldering on a retaining nut. Being pointed the cocktail stick fits through the hole to start with, then the heat of soldering burns away the bit of the stick which is wider than the hole. This gives a parallel wooden plug through the hole which both stops solder going where you don’t want it to, and ensures the hole is properly aligned. When fitting a retaining nut in this way, the hole in the plate needs to be the tapping size for the bolt that fits the nut. The last stage is to run a tap through the nut and the plate it is solder too, giving a continuous threaded hole through both. Back to coupling rods
Having re-drilled the crank pin holes from the back, the final side of the second half of the rod was made up of a separate crank pin boss from the Gibson etch, and the fluted overlay I cut off the crank pin boss/articulation pivot earlier on. I aligned the boss to the crank pin hole in the core rod with the cocktail stick, one end of the overlay to the boss, and the other with the filed away section of the core rod. This was about the only operation in the whole job where three hands would have been an advantage.
You should be able to work out how I finished the rest of it by now.
The articulation pivot holes needed to be opened out to fit the crank pin rivet (0.75mm). It was hard to drill a clean hole full size, so I drilled 0.7mm and finished off with a taper reamer until the rivet fitted. I still needed to clean some swarf out of the fork joint, so I used a spare bit of N/S as a file/chisel. Rivet the two halves together and bob’s your auntie. The picture shows a completed rod mounted back on the Avonside chassis jig to show that the axle centre dimensions are still correct. Theological diversion
You need to have spares of the rivets. They are devotees of the Great Carpet God and tend to fly off the workbench and seek sanctuary with him. I remain a believer in the GCG, even though it is some years now since I regularly modelled in a room with carpet on the floor, and became aware of the tendency of small metal parts to sacrifice themselves to this particular deity. In my house today, the GCG’s latest incarnation inhabits the cork tiles of the room in which I model, but he is still surprisingly adept at hiding those things which fly to him. My wife is the GCGs chief acolyte, and never, ever throws away any small metal fragments revealed when washing the kitchen floor.Final Thoughts Various
Once I’d done one set of rods as described above, the only thing left to do was the second set, remembering that connecting rods are normally handed and the second set will be a mirror image of the first.
Being a believer in the P4 “getting it all right” mantra, I filed off the fluting on the back of the rods, but even I began to think I was wasting my time.
The point about this whole forum thread was an attempt to convince other modellers that CSB’s were the simplest and best way to go when building loco chassis. I regret that postings like this do rather point to the personal pleasure I take performing rather than avoiding some quite fiddly construction tasks. This may be seen as undermining my original message. So I would like to point you all to a new section Russ has posted on the CLAG website called “CSB Gallery”
. This is devoted to pictures and notes illustrating many peoples’ implementations of CSBs. I think this gallery of photos is just the thing for showing people what can be, and is being, done with CSBs.
Having got the connecting rods finished, the next step must be to sort out the chassis frames. These will need quite a lot of thought, and possibly physical attention, before we are ready to start actually fitting CSB fulcrums etc. I haven’t started this yet so the next post could be some time coming. Until then, here is one final picture for you to be going on with.