Copenhagen Fields & TFW’s workshop

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Tim Watson
GER D14 4-4-0 'Claud Hamilton'
Posts: 309
Joined: Mon Oct 24, 2016 11:37 am

Re: Copenhagen Fields & TFW’s workshop

Post by Tim Watson »

A block of copper tungsten does present some challenges electrically for split frame pick up. This was resolved by cutting a slot for 7/8s of the length of the block. The slot was then filled with 24hr epoxy resin, with styrene ‘shuttering’ temporarily glued in place to constrain the resin. Once this had cured the remaining 1/8 was cut through and this section filled in with epoxy resin. It’s a technique I used for Mons Meg’s carrying wheel trucks, but the idea is based on the old fashioned way to make Hornby Dublo three rail wheels insulated: cut alternate spokes - fill with epoxy - then do the same to the remaining spokes. 
[URL=htps://hosting.photobucket.com/images/p707/strq0672/CA4E7E89-15C0-4BBE-A3B7-CE860E916577.jpeg?width=960&height=720&fit=bounds]Image[/URL]
The front axle does not have an external muff (as usual with 2mm scale wheels) but an internal 1.1mm diameter glass-fibre-reinforced  epoxy resin rod. The half stub-axles were drilled on the lathe to accommodate the internal rod (before my escapades with the styrene spoke replenishment). The rod will eventually be fixed with more epoxy resin, set to the correct back to back. The advantage is a scale diameter axle visible from the front. 
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The T nut can be seen in the background; this helps to control the ride height of the ‘bogie’ frames. I may use the 12BA bolt head (not visible) to locate a recurved spring to act on the centre of the rear bogie wheel muff to help its tracking. 

Tim
Tim Watson
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Re: Copenhagen Fields & TFW’s workshop

Post by Tim Watson »

The Raven NER 4-6-2 class has now run as a 4-6-2, albeit with the radial trailing wheels bouncing along for the ride. They will need a proper truck to control them.  The handmade bogie wheels were worth the effort. 
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https://youtu.be/-JhHM42VPMg

As ever, the phone picks up the noise of the mechanism rather well.  I have now sourced some 1/2” brass for the boiler; 3” of that should work wonders for adhesion.

Despite what some people say about them, I think that this engine will look rather elegant when complete. 

Tim
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Re: Copenhagen Fields & TFW’s workshop

Post by Hatfield Shed »

Tim Watson wrote: Tue Jan 10, 2023 11:43 pm ...  I have now sourced some 1/2” brass for the boiler; 3” of that should work wonders for adhesion...
There's an advantage with the length of the prototype and the drive line layout you have employed, ability to put the centre of mass above the centre coupled wheel. Is there a weight bearing on the couled wheels you are aiming at for adequate traction?

The model loco will look well enough, the smaller tender than that to which 'we' are accustomed to see behind pacifics: that might take time...
Tim Watson
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Posts: 309
Joined: Mon Oct 24, 2016 11:37 am

Re: Copenhagen Fields & TFW’s workshop

Post by Tim Watson »

All locos on CF have to be capable of pulling decent length trains, so they are simply made as heavy as possible. With a solid brass boiler this engine will easily tick the boxes. It may even be heavier than Mons Meg (engine weight 120g) which has shifted 26 carriages on the MRC test track, but that loco has the benefit of another pair of wheels.

Tim
Tim Watson
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Re: Copenhagen Fields & TFW’s workshop

Post by Tim Watson »

The last few days have seen the radial rear truck made on the NER 4-6-2 class. Looking at the works drawings, the virtual pivot point for this is just behind the middle axle, so this is where I located it, as the engine would not have a true radial-truck slide-way arrangement. 

The main components consist of the ash pan which acts as the bearing block for the back axle. The muff for the axle is 2.5mm diameter, and tapered at each end so that it can slide through the horn ways in the frames on an arc of movement.  The muff is full wheel back-to-back width to give it plenty of grip on the stub axles.  The front pivot is attached to the ash pan block using two, 0.6mm diameter, steel rods held in appropriate holes drilled just above the damper opening, with equivalent holes on the front pivot block. 
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The two rods allowed the radial arm(s) to pass either side of the gear wheel and are relatively stiff. It also allowed the pivot point to have a fine adjustment for radial length and then being  soldered in place. 
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The mounting for the pivot bolt is a piece of high density Tufnol made as a tight fit in the frames and then secured with 24hr epoxy resin. The insulating block is tapped 14BA and there is a bolt screwed in from the top (visible in this photo) that acts as a stop for the actual pivot bolt which approaches from the underside.
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The end result is a radial action which maximises the movement of the wheels, but in a well controlled manner, giving a smooth transition through curves. 
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The hole in the bottom of the ash pan is not to improve draft but to allow access to the lubrication point in the gear head.
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Having GA drawings is very useful when working out how to make a loco and I find it fascinating working out where everything goes. 
Image

Tim
Tim Watson
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Re: Copenhagen Fields & TFW’s workshop

Post by Tim Watson »

The main mechanical components of the NER 4-6-2 class are now complete. The final tweak was to add a couple of re-curved 33swg phosphor bronze springs on the rear axle of the bogie.  The wires are held in place with solder, but are located in holes drilled in the frames. 
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These springs have stabilised the front end by working not only as a downward forcr on the axle but also damping side play from acting on the sides of the central muff. They will also give excellent current collection.  Considering the great length of wheelbase on this engine it rides steadily through the reverse curves at slow speed without binding.  
https://youtu.be/5tWdtTl_S_0

Tim
Tim Watson
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Re: Copenhagen Fields & TFW’s workshop

Post by Tim Watson »

This is what you call a boiler!
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The boiler band positions were marked on the boiler using a gramophone needle held in the lathe (turning the chuck over by hand), moving to each position by dead reckoning (a digital readout helped). These witness marks make it much easier to position the lining transfers/boiler bands. 
[URL=htps://hosting.photobucket.com/images/p707/strq0672/F1ECEE91-6DB6-4770-8D0E-337BC72AF107.jpeg?width=960&height=720&fit=bounds]Image[/URL]
The engine currently weighs in at 105g. When the firebox, smoke box saddle and cylinders are added it will probably get nearer to the weight of Mons Meg (120g). 

Tim
Tim Watson
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Re: Copenhagen Fields & TFW’s workshop

Post by Tim Watson »

Some days you make a silly mistake which, by trying to fix your way out of it, wastes an inordinate amount of time. On the boiler for the long engine I milled away 1.5mm too much in the throat plate region of the firebox. I thought this could be remedied by soldering-in a packing piece. I did this but it was all looking a bit too scruffy, so I made a new boiler; which is what I should have done in the first place. 

The new boiler was shaped correctly this time and the separate firebox sides and top milled from a lump of brass to bolt to the rebate in the boiler.
[URL=htps://hosting.photobucket.com/images/p707/strq0672/1F9BBE88-3681-4281-9515-64B9BFE04F43.jpeg?width=960&height=720&fit=bounds]Image[/URL]
The sides are 0.5mm wider than the boiler and have a just-perceptible curve to them.
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The whole assembly was then silver soldered together. The poor fit at the foundation ring and footplate will be covered by forward side extensions from the cab.
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It is a very deep firebox, but that visual effect will be masked by the lower side pieces that will be part of the cab assembly. 
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She weighs 109g now. Smokebox saddle next. 

Tim
Tim Watson
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Re: Copenhagen Fields & TFW’s workshop

Post by Tim Watson »

Does this prove that 2mm scale modellers are nuts?
Image

Tim
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Re: Copenhagen Fields & TFW’s workshop

Post by Atlantic 3279 »

You're building a broaching loco to remove any obstructions to a larger loading gauge? :lol:
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Tim Watson
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Re: Copenhagen Fields & TFW’s workshop

Post by Tim Watson »

The bit of hex brass bar was drilled out and then bored to be a good fit on the smoke box. 
[URL=htps://hosting.photobucket.com/images/p707/strq0672/0176B918-6A30-45FA-A9E0-E27BF21BF8B3.jpeg?width=960&height=720&fit=bounds]Image[/URL]
The advantage of the hex bar is that it is easy to hold in a chuck and can be parted off to the required length. The front face was very carefully marked out for the two holes that would be the radiused corners of the smoke box saddle. I use a gramophone needle ground to a pyramidal-shaped tip. That way it is easy to ‘drift’ the centre mark to where it’s needed, rotating the tip to deepen it in the correct position. 
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The marked up block was easy to set up in the vice - an advantage of using the hex stock. It’s a bit difficult to visually ‘spot’ a 2mm drill in precisely the right place, so the drilling position was checked using a 0.7mm drill. The brass plug was a precaution against any lateral distortion when drilling with the larger size. 
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Once satisfied with the centering the holes were drilled at 2mm diameter. 
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The sides of the holes were milled away. 
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The side of the holes were used to guide a file as it cut down to the final position. It’s always useful having sharp files with safe edges. 
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The excess hex bar made a good handle as the base was carefully reduced in depth to maintain the correct height of the boiler and smokebox.
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The unwanted parts of the bar were removed using a diamond slitting disc and the flange smoothed into the up right part of the saddle. This was also rebated at the sides to take the scale frames that are above running plate level. Image
She’s beginning to look like a Skittle Alley now.
Image
Bit of a long post this one, but I thought some of my ways of working might be of interest. The next job will be to get it all bolted together. 

Tim
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Re: Copenhagen Fields & TFW’s workshop

Post by Atlantic 3279 »

Interesting certainly. To my cost conscious mind, the fact that most of the chunk of hex bar actually goes to waste was initially a concern, but then you are working in a small scale, so the waste is small.
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Tim Watson
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Re: Copenhagen Fields & TFW’s workshop

Post by Tim Watson »

Enough left over for another one! Lumps of brass always get used up in my workshop. It’s also useful to have a handle for working on smaller parts.
Image


Tim
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Re: Copenhagen Fields & TFW’s workshop

Post by Pebbles »

Why not make up two saddles, might become useful at a later date.
Tim Watson
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Re: Copenhagen Fields & TFW’s workshop

Post by Tim Watson »

One of the attractions of using the hex brass was that if the first one was unsuccessful I could have another go…
Not much to show for today’s efforts, but the long engine is bolted up together at the front end.
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It will need a couple of bolts at the fire box end to hold the boiler really well, but it is pretty stable already.
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I expected to have clearance problems with the frames, but it all just clears and the rigidity of the components will prevent any unwanted contacts. Even so, the wheels needed clearance cutting into the boiler cladding (as per prototype).
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Most importantly, it still works.
https://youtu.be/IuYy1q6CgBU

Tim
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