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Fixing the "Vomit Comet," Part 2.




The second instalment in this ongoing saga has been three years and two international moves in the making; thankfully the end is nigh, with no casualties as a result of a chassis catapulted in anger across the room. An update for those who didn't read part 1, I am slowly working through an 14xx conversion kit from the 2mm association for the Dapol model, designed by Chris Higgs in order to produce my first steam loco for use as an branch passenger train on the groups layout St Ruth and my own layout(s). Last time I had got to the point of fixing the motor, I did eventually get around to attaching the gears and wheels and painting that version, but the result was a chassis that still had a severe limp at one of the two speeds available, hence it seemed like a good idea to start again (again) rather than writing up yet another failure.


Hopefully writing up the trials and tribulations up will be a help to someone starting from fresh in the future anyway.


7. Too much time drinking beer, still


After the predictions from the last time I wrote about this kit, I have changed. I now drink Gin and Tonics too. In fact it helped more than once to go and have a beer instead of trying to muddle on with some infernal problem. Listening to the archers used to be a good excuse for a break too, but it’s gone all eastendersey now instead of the relaxing nonsense it used to be.


8. Go away and build some other kits.


I think this is possibly the most important step. The last time I had built the chassis, with the combined experience of a couple of BR 4 shoe chassis’ for vans and a mineral wagon starter kit. I’ve now gone through close to 40 wagons and a couple of coaches before starting this time. I have also invested in a temperature controlled soldering iron, and whilst I don’t usually vary the temperature, I think the feedback from the iron helps to control the amount of heat into the piece.


9. Strengthening.


Last time, the attempts I had made to give a little more rigidity to the chassis, after making it banana shape, involved soldering brass rods to the inside faces of the chassis sides, but this hadn’t really worked too well as there was still an weak point around where the spacers were placed. Taking inspiration from the more recent of Chris’ chassis, I took the last iteration of the chassis (MK7 or whatever, I lost count,) straightened it out, filed off some of the more protruding bits and used it as an overlay on a new etch. It helped to keep the new sides on the etch keeping them flat whilst sweating the two together using the bearings as alignment pins. If I was starting from scratch, I’d advise myself to buy two of the kits and do this again.


10. Simpson springs


I tried Simpson pickup springs again on the new chassis, using the same wire I used in the previous attempt. This time, however I drilled the bearings out to 1.55mm to give a little ’engineering tolerance.’ I also didn’t bother to fit springs onto the pony wheels, given that they should be relatively easy to retrofit if pickup becomes a problem later on, and liable to damage during the assembly process.
I tried to fit top acting wipers to the driving wheels, but in the end they were causing too much resistance on the wheels when testing. Possibly because there is very little room to fit them on the side frames meaning that they had to be sprung greater than they would otherwise be if attached above the wheel.


11. Assembly


Having overlain the chassis, the supplied assembly jig was now useless as it would not fit in between the slots. The association chassis assembly jig was pressed into service to help keep everything square. However all is not as simple as it seems, as pointed out on the VAG some time ago, the central spacer on the jig is designed to set the spacing for PB frame material and not for the PB Bearings (which were coincidentally, just about, protruding through the double thickness chassis.) This was solved using a piece of square tube of approximately the correct dimensions with a perpendicular(ish) hole drilled through the middle. It would be nice to get a new pair of spacers to fit the jig turned on a lathe, to get everything entirely square and accurate but this’ll do for now. The spacers were then soldered underneath and on the top, wicking the solder up to meet the sides of the chassis creating a, on the whole, more solid joint than just attaching to the folded tab on the top.




12. Motor and gear selection.


Chris suggests using the Association flat can motor for all of the kits, however having heard many good things from Jerry and Ian, this time I plumbed for a Nigel Lawton micromotor. It’s true that not many motors would fit in the 14xx body, the Faulhaber 1016 wouldn’t fit, but the micromotor does and seems to handle a chassis with more stiction at lower speeds better than the flat can motor. I used a quality engineering approach to attach the motor to the chassis again this time, it’s epoxied onto a piece of plasticard epoxied onto the chassis. It helped to runs some volts though the motor whilst there is still some plasticity to the glue to get the worm and shaft all aligned with minimal binding. As the motor is closed there was no need to worry about paint getting into the internal mechanism too.
I originally used the now discontinued imperial 30:1 imperial worm set and in the spirit of starting again I replaced this with the metric 30:1 set with a brass worm gear, which seems to have solved the meshing problems seen in the previous incarnation along with a more diligent assembly of the etched gearbox. After pushing the driving gear onto an new muff I epoxied it in place which stopped it from skewing, or at least to a lesser extent, as I believe that this was the primary issue behind the bad running in the first place. I think it helped to only push the gears onto a muff once, as after this I think there is too much horizontal slop, which means the gears don't mesh properly together.
The modifications to the chassis spacing meant that it was necessary to file back a part of the gearbox supports and reverse the order of the spur gear and wormwheel gear, but all’s well that ends well.


13. Coupling rods and crankpins.


In stripping the old chassis, I took the precaution of removing the old pins from the wheels and starting again with these too. This time I used the flanged crankpins instead of the normal crankpins in an effort to keep them square to the wheel from the outside face. After fitting these it was time for another polish. I only managed to stab my hand with the crankpin once whilst it was spinning in the minidrill…
On the last assembly, I had decided that the old coupling rods were irretrievably bent, so new ones were fashioned from the generic stainless steel coupling rod etch from the association. Unfortunately there weren't 14mm spaced rods on this etch, so a hole was drilled through the coupling joint in one of the pannier sets. I think that this bodge may have resulted in a spacing that may have just been a tad off still, so these were retired with the arrival of a completely new etch.
The new coupling rods were sweated together with a thin layer of solder between each of the layers, copious flux, pressure to ensure that all were aligned flat and plenty of heat. The holes in the coupling rod were then opened out slowly with a reamer until they were close fit on the crankpins with minimal slop. Rather than shortcutting to get to a running chassis underneath the body, with insulation washers, this time I kept the crankpins at the original length. Once happy that everything was running along nicely, I soldered the turned washers on and used the edge of a thin track file to cut the rest of the pin off, with the minimal of displacement.


14. Quartering jig.


It’s worth every pound in my opinion. Yes the wheel s will still need a little adjustment afterwards, but the wheels will be safely pushed on without distorting the chassis or crankpin square-ness which I was extremely careful about in this build.




15. Lubrication.


Having applied some power to the wheels, I was astonished to find everything moved as it should. I then ran it up and down my test track on full speed for an half an hour or so, (more in amazement than actual planned running in.) I’d probably put some oil on the gears straight away next time as there were some suspiciously bright spots on the worm gear following the initial run in. Strangely, slow running improved a hundredfold after I had applied some oil (I think I shouldn’t have used bicycle chain oil, but it’s all I had and seems to work fine.)


And so that’s it… probably not some of the best practices in loco building, but I managed to get a chassis to work smoothly at an reasonably low speed in my opinion, without resorting to a backhand deal with a deity.


A small drawback that was found after finishing, possibly as a result of using the flanged crankpins, was that the coupling rod washers were fouling the body when it was sitting down on the chassis correctly. This was rectified by cutting the body around the crankpins giving them clearance but upon reflection was probably caused by the use of the flanged crankpins over normal ones.
I also made some modest improvements to the Dapol body: filing off the bottom of the boiler, replacing it with a piece of brass tube, gluing on the etched bufferbeams and replacing the handrail on the boiler, hence it looks a little more like a reasonable likeness to the prototype. I don’t really want to do too much more though, renumbering to 1419 (or 1434 if I want to stick the top feed on) adding some of my personally mined coal and touching up the new paint is probably all I will manage without a complete repaint and the dreaded lining.


Stuffing as much tungsten putty into every orifice available in front of the centreline also seems to enhance adhesion to the rail and may even mean that it can pull a couple of autocoaches along quite happily. It may also mean that the rail doesn’t have to be completely spotless to ensure that something moves. I don’t think it’s going to be the next yard shunter on St Ruth, but as long as I don’t have to follow it with a finger on the branch passenger run, I’ll settle for that!



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A very nice write up.  Glad that perseverance finally paid off, she looks lovely.  I look forward to seeing her trundling back and forth on St. Ruth next time you're back in the UK.


As an aside, neither Jerry or I bother with the resistor supplied with the Nigel Lawton motor (I don't think John Greenwood does either).





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Looks good. How many etches did you get through in the end? I lost count.


Resistor... me neither.


Maybe a nice simple pannier next?

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Thanks Both, I'll forego the resistor next time too methinks. still just a couple of bits to get around to before I bring it back. Just the two sets of etches, soldered and stripped many, many times.


Maybe a nice simple pannier next?


Isn't there a race on between John and Steve?


Best Regards.



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I just noticed that your blog doesn't appear in the RSS feed on the 2mm website. It really should.


If you drop a mail to [email protected] (Nigel) then he will add it.

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Isn't there a race on between John and Steve?


There was.  I think John won - his pannier has been seen running on St Ruth.  Steve's J94 was having another rebuild last time we spoke (it may even be a new chassis kit), and Steve is having a bit of a dalliance with things somewhat larger too.  I don't think any drink has been provided to the winner by the loser yet though :-)

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There was.  I think John won - his pannier has been seen running on St Ruth. 

Pity he hasn't written it up then!


I just noticed that your blog doesn't appear in the RSS feed on the 2mm website. It really should.


If you drop a mail to [email protected] (Nigel) then he will add it.


Would this mean a commitment to write more than once per year?



Now I know why these chassis are selling so well - you are consuming multiple examples!


why buy one, when you can get two, to support your friendly association...


Best Regards



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Don't feel too bad about the progress of your loco. I bought a Langley 14xx & Autocoach kit back in 1983.  I still haven't finished it.  Most of the intervening period was spent doing step 8.



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Good choice with the Gin Tonics - although I drink less of them since leaving Spain.


As ever, good to read your updates Chris :good:

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