7mm On Heather's Workbench - a baby Small Prairie

Discussion in 'WR Action' started by Heather Kay, 2 August 2017.

  1. Heather Kay

    Heather Kay Western Thunderer

    Ta. Yes, it’s the camera angle. The brackets could be tweaked a little forward, though. I’ll ponder that for tomorrow's fun and games. ;)
  2. Dog Star

    Dog Star Western Thunderer

    No and that is correct.

    The motion bracket is a lap joint to the frame stay, the joint being behind the hanging bar.
    Peter Cross likes this.
  3. Peter Cross

    Peter Cross Western Thunderer

    Thanks that's handy to know. It just looked a long way out, from the angle of the photo.
    TommyM and DrIain like this.
  4. Heather Kay

    Heather Kay Western Thunderer


    Things were looking good. I worked out that the PRC detailing set included the nut thingies on the ends of the cylinder casing. I fitted them, filled the odd hole here and there, and fettled a little bit. I sorted out the connecting rods, and assembled everything on the chassis to see if it all worked.

    I had managed to achieve a lovely smooth crosshead action. Clearances didn’t look too bad. One thing, however, came to bite me in the rear: the slidebars, which I had fitted making some assumptions, were too short. The crosshead was peeping out the ends with the crankpin at full back position. Oh, bother. That would explain why I had to move the cast bracket locations.


    So, here we are at coffee time on Friday morning. I’ve decided, reluctantly, to substitute the PRC slide bars for the JLTRT ones. The PRC ones are lovely, but very soft, and I am worried further fiddling may cause breakage. I’ve also trimmed them short a couple of millimetres, albeit inside the cylinder block, and making things right there will be a chore. Some careful filing will commence shortly, after my shot of caffeine and chocolate biscuit.
  5. Heather Kay

    Heather Kay Western Thunderer


    The little-known, and sadly entirely unsuccessful, Churchward 0-2-0T. With the intention that the type should be able to traverse very tight radii on bucolic branchlines, it was found impossible to balance the thing successfully, not helped by water sloshing about in the tanks.



    After a morning of careful filing, the replacement bars are in, and it looks like this is going to work. The driven axle has been fitted, and the crossheads attached to the connecting rods, to manually roll the wheels about to test. Apart from a mild tight spot here and there, it all looks good. I need to reattach one motion bracket, and then reassemble the cylinder block, but I think that’s a satisfactory outcome.

    Sometimes, there is simply no alternative to sorting out problems save by essentially starting again.
  6. daifly

    daifly Western Thunderer

    It's been done already!

  7. Heather Kay

    Heather Kay Western Thunderer

    Ah, the joys of S7 tolerances.


    I set about crankpins and nuts today. The leading crankpin nut has to be recessed, and my starting point was a set of cast CPL nuts. Plenty of careful filing, some careful countersinking, some more filing, drilling a couple of tiny holes so the nut can be tightened with fine tweezers… and this is where I’ve got to. Barely a fag paper between the slide bars and the crankpin nut. The front wheels have almost zero sideplay, too.

    You would be correct in thinking I could skim some more off the back of the nut, make the countersink deeper, and all manner of other things. I will have to do that anyway, but I think it highly unlikely there will be space for the crossheads to fit even so. It’s those coupling rods that are exercising me at present. They’re so resolutely flat and wide. They need to be scalloped on the backs to clear the wheel bosses. You can see in the photo I’ve got two washers in there to give the clearance. Here’s my conundrum.

    The PC rods could be machined out a mill or so. I’ve checked their five year old site - pleased to note they shall be attending the Reading Trade Show in December 2013! - and they don’t seem to specify scalloped rears. I could, finally, fall back on the etched rods, but as far as my brain cell can see they wouldn’t be easy to make up with a correct knuckle joint, hinging rather on the crankpin itself with cosmetic knuckles. As I’m driving the centre axle, perhaps this won’t be a problem. They would at least, be plenty thin enough to give me more space where it’s needed.

    Time for some consultation and cogitation.
  8. Peter Cross

    Peter Cross Western Thunderer

    Have you tried the crosshead and conecticon rod on there. To me it looks like the crosshead will be Infront of the crankpin. Or at worst only the very rear end of it. I could well be wrong but I would be checking before going to far. Are the slide bars parallel to frame or is it photo moving things out of line.
  9. Heather Kay

    Heather Kay Western Thunderer

    I have tried, Peter. Sadly, they do interfere with each other. :(
  10. Peter Cross

    Peter Cross Western Thunderer

    Oh bu@@er. I must admit I have spent time in the past thinning down things, only to find I could of done less than half the work to make it work.
  11. adrian

    adrian Flying Squad

    They don't need machining - just a few minutes work with a 6" file would do the job - a half round needle file just to blend it back into the boss.
    Heather Kay likes this.
  12. Heather Kay

    Heather Kay Western Thunderer

    I might have a go at that. It’s just holding the things properly where my technique falls down.

    Having consulted, it looks like we may well headed along the etched route if filing doesn’t work.
  13. Ian@StEnochs

    Ian@StEnochs Western Thunderer

    A block of wood and a few small nails through the crank pin holes into it will hold the rods while you file. Get a decent sized file too, at least 8” 2nd cut, with a proper handle and keep it away from steel and white metal. Don’t waste time with needle files except for the radius at the boss.

  14. simond

    simond Western Thunderer

    Or solder it to a bit of sheet brass, and screw that to a bit of wood.

    More cleaning up to do afterwards, but a secure grip that won’t damage the rods.

  15. Heather Kay

    Heather Kay Western Thunderer

    Okay, I’ve been assessing things.

    The jointed PC rods can be filed back to give the scallop. However, the knuckle joint also needs to be thinned down as it needs to pass the centre wheel boss, which will probably compromise it. It’s a simple lap joint, not slotted like the real thing.

    I have another set of PC rods which hinge in the crankpin. The same issues there with the centre joint area and wheel bosses.

    The etched rods have holes too big for the bushes, and that’s before I even think about removing cusps. Oh, fudge!

    What do I do now? I’ve run out of ideas.
  16. simond

    simond Western Thunderer


    I feel your pain. Some suggestions, more in hope than certainty;

    You don't need to care about the middle joint, if you can thin the leading crankpin enough, you can get clearance behind the crosshead. If the middle crankpin is a few tenths outboard of the leading one, nobody will be able to see, and it won't matter a jot from a geometry point of view.

    So, I would not modify the centre or trailing crankpins, rods or whatever, but simply use a Slaters bush with flange to the wheel for the coupling rod, and another flange outboard for the connecting rod.

    I'd stick with the Premier rods.

    How thin can you make the rod where it crosses the leading wheel hub?
    I think you've already recessed the rod where the crank-nut fits, I did this on my 1366, and used a Slater's bush, arranged so the flange and bush were fully within the thickness of the rods. DLOS also did this, he made a nicer "more professional" job of it than I did, he machined the holes in the crank nut and made a peg spanner to tighten it. I use filed notches & tweezers!
    Can you put an axle in the lathe, and skim the front of the wheel around the hub? If will still need to be proud of the rim, but I guess a few tenths can be taken off there. Youll probably have to deepen the countersink in the wheel to get the screw in deep enough, possibly also the countersink in the axle ends too.
    How thin can the flanges on the back of the crosshead be - I'd guess 0.25mm might be tight but do-able?
    Can you thin the slide bars sideways a little? A few swipes with the file may gain another tenth or two? But that might suggest that you'd need to make the crosshead slots thinner too, otherwise it will be free to move in and outboard, and that's more difficult.

    hope this helps
  17. Heather Kay

    Heather Kay Western Thunderer

    Simon, thank you. All sorts of grist to the mill.

    Some of your suggestions will be attempted shortly.
  18. Ian@StEnochs

    Ian@StEnochs Western Thunderer


    If you decide to use the etched rods, and often they are better looking than milled ones, it is quite easy to bush the etched holes with a piece of brass tube. I often do this for a number of reasons.
    It gives a better bearing surface than multi layer etch.
    It gets over the ‘hole etched too big’ problem.
    It strengthens the joint, especially if one needs to counterbore for a recessed crankpin.
    It is easy to compensate for holes etched at the wrong centres. To do that I set up the chassis jig with the axle hole centres and then using the reduced end rods with short pieces of brass tube slid on and the rods adjusted to fit before soldering and cleaning up.

  19. Heather Kay

    Heather Kay Western Thunderer

    Thanks Ian. I thought of that, but of all the brass tube stock I have, nothing was the right size.



    I’ve taken a bit off the rear, so far, of one leading coupling rod. A nick was needed out of the back of the leading oil pot to clear the boss on the down stroke. I’ve also run a file a few times across the back of the crosshead casting. I have to say, I think I’m winning. I can roll the chassis along and everything works. A little more finessing, and I think I will call it a success, and repeat on the other side.

    Before I head off to the bench again, a thank you to everyone for their suggestions and explanations. My black dog had taken up residence sometime yesterday, and I was not in a very happy place this morning. Persistence is beginning to brighten the mood, and I feel much happier about things now I’ve got this perisher sort of working at last. I have intimated to some of you off the forum that I really don’t enjoy working with locos. Making them look nice is fine, but making the things run tests my patience sorely. Once the current crop of them in the queue has been dealt with, I shall concentrate my efforts on coaches, where I feel I am able to cope with most things.

  20. Heather Kay

    Heather Kay Western Thunderer


    I shall sleep soundly tonight!