TFW’s workshop

Discussion in '2mm Lounge' started by Tim Watson, 11 November 2017.

  1. Tim Watson

    Tim Watson Western Thunderer

    After a day demonstrating fine scale stuff at the MRC, Keen House, yesterday, I now have Valour running with the connecting & coupling rods in place. The wheels and chassis are chemically blacked, so they shouldn’t need to be removed any more.
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    Demonstrating wheel quartering live, on camera, is surprisingly stressful; I can demonstrate dental operative procedures much more easily.

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    Tim
     
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  2. Tim Watson

    Tim Watson Western Thunderer

    I wasn’t quite happy with Valour’s coupling rods as, on filing away the etched cusp, they came out too skinny, especially when compared to the beefed-up connecting rods.


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    So I have fitted strips of 5thou nickel silver to the top and bottom of the rods.

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    This makes them much stronger; especially over the pivot joint and also closer to the chunky GC appearance.


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    Much happier now. Anyone who has the etches from me could avoid this extra work by filling the cusp with solder and being less fastidious with the filing.


    Tim
     
    Last edited: 21 July 2019
  3. Tim Watson

    Tim Watson Western Thunderer

    The self trimming tender for Valour has made some progress over the last few days in Cornwall. The etched components fit together reasonably well, assuming that the slots are opened up a little and the tabs thinned down.

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    The top of the sides are soldered up from two components to give the beading - this is quite clever, but a little bit tricky.

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    I have cut out various parts of the tender internal structure to make room for the motor and flywheel, which will be attached to the chassis. It was probably easiest to solder the side sheets on at this time.

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    The tender top will have a variety of details added such as the water scoop mechanism covers, bulkheads and toolboxes.

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    Tim
     
  4. Tim Watson

    Tim Watson Western Thunderer

    The self trimming tender is designed to make the fireman’s job easier by the use of gravity. A better name might be a ‘hopper’ as it looks rather like a grain store. The etches make up this complicated structure with a bit of judicious filing and fitting, certainly nothing a bit of solder won’t sort out.

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    The top is still loose and is a good passive fit. It will probably stay that way until I have the chassis and motor in place.

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    It is really easy these days, working with small 8mm diameter x16 mm long motors. Quite a far cry from 40 years ago when we started squeezing Portescap 1219s into tenders.


    Tim
     
    Last edited: 2 August 2019
  5. P A D

    P A D Western Thunderer

    Hi Tim,
    Looks good.

    As the motor is so small, is it not possible to put it in the loco with the gearbox and avoid the need for the shaft drive from the tender?

    Cheers,
    Peter
     
  6. Tim Watson

    Tim Watson Western Thunderer

    That is an option nowadays, Peter. That is what I did with Mons Meg. However, with Valour I wanted to keep the back end of the boiler and firebox filled with heavy metal. The motor is very light and doesn’t help in the traction department. The weighted tender body will probably also weigh onto the back of the engine. UJs are not a problem in 2mm scale and, once spinning, 10thou wire is all but invisible.

    Tim
     
  7. Tim Watson

    Tim Watson Western Thunderer

    The tender chassis and motor mount have made good progress this week.

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    The 8mm Tramfabrik motor has an old fashioned ‘stay alive’ brass capacitor on the end. The outer shroud of the UJ has not yet been made for the ? shaped drive shaft.

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    The motor mounting block is bolted to the chassis, taking care, of course, to avoid shorting out on the frames. The reason for the strange shape will become apparent.

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    Obviously, the coal space will have a cover over the motor & flywheel.

    Tim
     
  8. Tim Watson

    Tim Watson Western Thunderer

    The tender frames as etched in the kit have a half relief for the springs and a clever fold-up system for positioning the side valance at the same time as the frames, as can be seen at the top of the picture.
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    However, I wanted to widen the distance between the frames by about 0.5mm to give the tender chassis a bit more space for freedom of movement. I was also not overly keen on the half etched ghosts of the axle boxes & springs. So I turned the frames round and cut out a strip of 0.85mm thick brass, 1.9mm wide, to make up the valance. These strips were soldered on to the running plate, giving it a bit of extra strength. The frames were then soldered on to these, again giving a much stronger structure. (The loose tender top is not quite seated home in the second picture.)
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    This increase in rigidity of the tender sides has allowed me to tidy up the insides of the tender rather well.
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    I may hang the tender on the back of the engine to increase traction which has caused me to think about arrangements for allowing the tender chassis to run semi-autonomously - I do enjoy working out these sort of challenges. The tender body is currently very light, but there is plenty of room for some brass or copper tungsten weights.


    Tim
     
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  9. Tim Watson

    Tim Watson Western Thunderer

    After a bit of pondering, the tender and engine are now coupled up. The tender chassis is free to move up and down at the front, being restrained by a pin, but can pivot / rock at the rear. The body weighs down on the back of the engine via a very precise coupling which moves sideways easily but has very little play vertically.

    The tender - engine coupling looks quite simple.
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    The back pivot is a domed shape, tapped 12BA, that engages in a dimple in the PCB of the chassis stretcher - effectively a ball and socket with a bolt through it.
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    Soldering this brass turning to the tender body was easily achieved using the 12BA HSS tap to locate it in the hole (this was also tapped). Soft solder will not stick to high speed steel - but as a precaution it did have residual cutting fluid on it.
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    The front end pin was a 14BA bolt soldered to the body work, running in a hole in the PCB stretcher, visible in this dismantled shot. The bolt was surrounded by a shouldered tube to give a smooth surface, as can be seen. The length of the tube was long enough to give generous vertical movement of the front of the chassis.
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    The shoulder is designed to just accommodate a 20thou thick draw bar and 8thou washer, with a 14BA nut and lock nut (as insurance) to hold it all together.
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    The end result can be seen in this photo: holding the engine in thin air, by the tender.
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    The loco has similar pivot arrangements. The fall plate from tender to engine will also be used to stiffen up the joint in the vertical axis. The tender chassis should track OK, as it has quite a bit if weight on it with the motor mounting block and flywheel, whilst the tender body will have more weight added to it to help adhesion. If it all proves unnecessary, then the fixings can be converted to a rigid system with ease; but tricky to engineer these sort of things retrospectively.

    Tim
     
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  10. Tim Watson

    Tim Watson Western Thunderer

    After cracking on with the UJs, Valour is now powered from the tender. These are the standard ? type for my locos. The end cap with the hole in it helps to keep the UJ in one end: it will be pushed fully home when construction is more complete, to be behind the coal space opening.

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    It ran well enough under power and, after gapping the PCB in the correct places and connecting the motor leads, it should be good for dragging itself along the tracks.


    Tim
     
  11. adrian

    adrian Flying Squad

    Impressive - although there seems to be a little oscillation in the drive system. Presumably this will be tuned out by tweaking the loops at the end of the drive shaft.
     
  12. Tim Watson

    Tim Watson Western Thunderer

    Plenty of tweaking yet to come Adrian, but pleased it went straight off with no drama.

    Tim
     
    adrian likes this.
  13. adrian

    adrian Flying Squad

    and why not - it's an impressive build. I remember my Dad scratch-building a Valour but that was in 7mm scale with plenty of mass and room to stick a nice motor in the firebox. I think at that time we were splitting efforts in that I'd build the tender and he built the loco. The tender was straight forward but for the loco the entertaining bits IIRC was getting the front footplate fall plate looking right and the windows in the cab and the front spectacle plate being the tricky areas to capture the look of the loco not forgetting the nice little flare at the bottom of the spectacle plate onto the footplate.
     
  14. Tim Watson

    Tim Watson Western Thunderer

    Valour can now pull itself along the test track. Pickup is currently (ouch) only from the tender. The flywheel imparts about a revolution of the driving wheels when she is stopped from a reasonable speed.


    I am very content with the running, with the tender picking up well on its own and the body riding steady and stable. There isn’t any significant weight in the engine, whilst the tender is very rattly with little weight to bear down, so performance should improve with more weight from both.


    Tim
     
    Last edited: 6 August 2019
  15. Threadmark: Annoying noise
    Tim Watson

    Tim Watson Western Thunderer

    I wasn’t happy that Valour was noisier than it should be, but at certain speeds it would quieten down. I traced the noise down to the fact that the motor has quite a bit of end play on the shaft and the back of the flywheel was slapping the bearing face at certain speeds. The flywheel was removed (by putting the soldering iron on it at 450 deg C to kill the Loctite) and was then advanced down the shaft by less than 0.5mm. She now runs with just the rumble of the gears and also free-wheels better. Noise = inefficiency.


    Tim
     
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  16. Tim Watson

    Tim Watson Western Thunderer

    It’s only a small part of the total, but getting an engine with a front bogie to track correctly requires a means of supporting and restraining the front end, whilst at the same time allowing the driving wheels to maintain traction.


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    This little pin, spring and curved slot should do the trick for Valour. The bogie side frames are made up in layers from the etch and the pivot is actually a 14BA bolt, with the threads reduced in the turning areas so as to reduce friction. The slot is tapping width for the bolt, which screws through it into the shouldered brass pin which also restrains an N gauge coupling spring for downward pressure and a little side control. A washer is soldered to the spring to prevent it insinuating itself through the slot. I think it is advantageous to have the bogie slot at the bottom of the stretcher, rather than the top, as it will give better stability.


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    The central brass pin is located in the PCB spacer between the cylinders and soldered to it’s top and bottom sides, respecting electrical neutrality of course.


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    It is evident that clearances have had to be made for the bogie wheels, which are scale size at 7mm, but of course with oversized flanges. Experience has shown that clearances need to be far more than you might think!


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    Having the bogie on the front begins to give Valour a racy look. The white muffs will be replaced with a scale axle at the front and a small black muff at the rear.


    The video shows the bogie in action.

    Tim
     
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  17. J_F_S

    J_F_S Member

    I like it - just the way it should be!

    Excellent stuff here as ever.

    Best Wishes,

    Howard
     
  18. Grahame Hedges

    Grahame Hedges Active Member

    Mind boggling micro-engineering excellence. Super stuff.

    G
     
  19. Tim Watson

    Tim Watson Western Thunderer

    Thanks for the kind comments. Moving on to the engine bodywork, that clever Mr Easton uses a cradle to support the running plate. This makes it pretty simple to assemble. I did, however, use my own piece of larger 5thou NS sheet for the change in direction of the running plate behind the raised cylinder section - this will get trimmed to size later on. The supplied squiggly bit was just too small and fiddly.

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    Similarly, the front steps were made out of 5thou strip, being much easier to hold as well as being closer to scale thickness: they are quite large and thin on the real thing. The strip is held in place but notched where it needs to break before soldering into place.

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    The piano front between the frames was made from som 0.6mm thick NS filed to shape: it took quite a while to get it nice and snug.

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    Will soon separate the running plate from the jig and offer it up to the chassis. Kits certainly speed up construction.


    Tim
     
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  20. Tim Watson

    Tim Watson Western Thunderer

    The running plate is now mounted on the chassis with three bolts to locate it. She now begins to look like an engine.

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    Thin double sided PCB, tucked up behind the valence, has been used to insulate the front running plate from the cylinder assembly. The smoke box will bolt through the PCB.

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    Tim