Copenhagen Fields & TFW’s workshop

[Tim Watson]

Work on the wavy, cascading, front running plate for the NER 4-6-2 class has been started. It is quite a challenge to keep such structures level and so the foundations are made from three pieces of 1.4mm thick brass silver soldered together: this will represent the valence on the edge of the running plate.  Cutting in the concave form at the front of the running plate was achieved using an old steel finishing bur (they used to be used in dentistry) the surface irregularities were then tidied up with a fine round file.

The components were set up a charcoal block ready for heating up, held in place with pins from broken drills. The solder paste can be seen in the middle joint - the other had been made previously. Powder borax flux is also added. The flame I use is a little gas torch - similar to the ones used to burn crème brûlées.

Removed from the block and cleaned up. The rebate at the front of the concave forms will take the 5thou nickel silver running plate tops: these will have the fine details on them and, of course, the driving wheel splashers. 

The smoke box saddle will be bolted through at the front, not surprisingly, It will be a solid lump of brass. In fact, I suspect this engine will weigh in heavier than Mons Meg. 

Finishing with a bit of an arty shot with the running plate approximately held in place. There are sacrificial stiffening spacers that will be cut away once the back end is complete.


Tim

[Tim Watson]

Sorry to be a bit repetitive but after a productive session today the running plate core now complete for the Skittle Alley: now becoming an exceedingly long locomotive.  The rear section was bent up and butted up to the middle. The hole in the stretcher is to take a locating pin when silver soldering.
 
As before, the components were set up on the charcoal block and held in place with pins from drill shanks. 
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In this photo the solder has just flashed: the flame and residual hot charcoal are visible.

After cleaning up, but before removing the stretchers. 
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These were removed with a fine diamond disc.

Now set up on the engine. 
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Whilst this has part of the engine represents a good deal of work, it does give a solid foundation for the loco body. If it were etched, a sacrificial assembly jig would help in construction (as with Valour). If it were 3DP it would be simple to make. However, neither would be as strong as this solid brass assembly. 

The valence will be reduced in height by 0.2mm when I have fresh pair of eyes. 

Tim

[Tim Watson]

Duplicated post.

[Dave]

Tim you shame us all I can't believe that is 2mm scale, just amazing.

[nzpaul]

Fascinating as always Tim. I'm curious about the flexibility of the chassis. It appears to be a 2-10-0 as far as rigid wheelbase goes. Do you build in any sideplay for cornering purposes, or is CF big enough to allow a long rigid engine?

Paul

[Tim Watson]

It will effectively be a 2-2-6-2, Paul. The front bogie wheels will be a pony truck with the back bogie wheels free to go up and down with a little side play. This is because the clearances behind the cylinder and slide bars would be too tight for a conventional bogie. The rear wheels will act as a radial truck with a long pivot.

Copenhagen Fields has a minimum radius of 600mm (2’) on the main running lines which is quite adequate for most stock. The rule that a foot radius for every millimetre of scale is quite a good one for trouble free ‘scale’ running: e.g. 4’ radius for 4mm scale.

Happy New Year everyone!
Tim

[Tim Watson]

After a great deal of fettling and fitting the running plate core is now fixed solidly to the chassis for the Raven NER 4-6-2 class. It had to be lowered quite a distance, compared to the starting position, and was also reduced in thickness by 0.25mm. 

There are two 14BA fixings, one at the front, one at the rear. The body is live to one side of the engine. It was important that the rear fixing could give stability and so a thin strip of very thin PCB was soldered to the top of the ‘insulated’ frame where the stretcher sat.  The fixing bolt was then well greased up (as well as the associated tapped hole) and some cling film wrapped around the body section. Slow setting epoxy resin was then placed on top of the spacer, the body positioned and the bolt tightened up through the epoxy resin; squeezing it between the cling film and the chassis - effectively making an insulated bed for the body to fit onto. The whole assembly was cooked under a couple of hot spot lights for an hour. 

The body was removed from the chassis well before the resin had completely cured and any excess trimmed way with a scalpel.

The clear resin doesn’t show the seating very well, but it does give a nice solid fixing for the rear bolt. The wheel clearances are obviously fairly tight  and so accurate fixing for the body is essential, if scale widths are to be maintained. 


I have worked out how the bodywork will be made: mainly as subassemblies, to ease the painting in NER livery, which was slightly more complex than the LNER style. That being so the smokebox saddle and boiler could be next or maybe the radial truck at the back. Just need to make my mind up… I must say how enjoyable it is to be making an engine from scratch again. I find the problem solving the best bit.

Tim

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[Tim Watson]

Well, I changed my mind. The front bogie wheels had been giving me pause for thought as they are of typical NER pattern 12 spoke at 3’ diameter.
(Photo courtesy Blandford 1969 from RMWeb)
The Association only makes a ten spoke wheel at that diameter. 

There is a school of thought that says you never see the spokes when the wheels are going round. That is perfectly true, of course, but it somewhat irritates me to see the wrong wheels under an engine, especially when they are so characteristic of a particular railway. I have made wheels in the past and was resigned to turning up some steel blanks for the purpose. It then occurred to me that the ten spoke wheel could easily by converted, so eight of the spokes were cut out with a piercing saw: one cut near the hub, the other at the perimeter. 

The cutting scars were filed away and the hub reduced in size as well as the rim: I wanted the spokes to be as long as possible - many model wheels are too heavy in these areas. 

The ten replacement spokes were made from 10thou black styrene cut into a small rectangle that was very slightly trapezoidal in shape. This gives just a slight friction fit between the hub and rim. Setting up these spokes was easy, they were in essence a clock face. The penultimate styrene spoke can be seen ready for placement on my finger tip. 
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Once the spokes were in position a minute drop of ultra low viscosity cyanoacrylate adhesive was flooded into the end of the spokes, using a fine pin. Super glue can be slowed down in ‘going off’ by placing a drop onto a plastic bag to pick up from. Once set, the spokes were trimmed to shape using a scalpel and an ultra sharp chisel. 
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The wheels were then given a coat of NER green: they are looking a bit vulgar in this photo. The wheels will hopefully look better when the rims and hub are black. 
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Worth all the effort? A few hours work - what do you think?

Tim

[nzpaul]

Worth all the effort? A few hours work - what do you think?

Tim

Well, we can't question your commitment to making it as accurate as possible. Your display of skill is inspirational, not just to me I'm sure.

Paul

[Atlantic 3279]

I'm impressed. Presumably one has to avoid being at all heavy-handed when cutting out the original spokes, when handling the skeleton wheel, and when installing the new spokes in order to avoid finishing up with a wheel that doesn't run true? How on earth do you get the new spoke lengths just right to be a good fit when the "trueness" (or not) of both the hub and the rim have been achieved by hand filing?

[Tim Watson]

The landmarks of the hub and the steel rim gave a good indication of where to file to. The brass was actually quite strong, even with only two spokes remaining: my previous hand made wheels have used a steel core and so are a bit stronger. Any minor variations in spoke length were accommodated by trimming the spoke itself. Concentricity is never compromised, because the styrene exerts negligible force, but the wheels are handled gently until complete.

Tim

[Tim Watson]

There are an awful lot of spokes for such a small wheel.

Tim

[manna]

G'Day Gents

Unbelievable workmanship.

manna

[Tim Watson]

Work has continued on the front bogie / pony truck for the long engine. The rear bogie wheels have a vertical slot to move up and down. The front pony truck started out as a lump of copper tungsten (heavy alloy - upside down in this photo).

The 12BA rear pivot and axle hole were drilled in the roughed-out block so that the whole engine could be tried out on my test track minimum radius, before committing too much effort. 
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The test track was actually a section lifted from Chiltern Green 40 years ago and is substantially below the 600mm radius on CF. It all fits on the curve, but I dare say there will be some squealing - especially with a solid 1/2” diameter brass boiler sitting over the top. 

There is a lot of work to finish off the ‘pony’ truck, but at least it now looks a bit more joined up at the front. 

Tim

[Tim Watson]

Today’s saga sees the pony block trimmed into a functional relationship with the chassis after a good deal of milling and filing. The frames at the front of the bogie are open, with the springs, front axle boxes and associated keeps visible. 

In order to make the frames thinner at the front from the inside I used a sharp file, but had a piece of brass underneath to support it and act as a runner so producing a neat rebate, by filing on the side. 

The end result then gives space for the front guard irons. These were made from brass, as copper tungsten is a bit brittle in thin section.  It’s always easier to make small pieces with a handle and then chop it off. 

Copper tungsten does not soft solder but will take silver solder, as can be seen with the components pinned down on the charcoal block. 

The ‘pony’ set up can be seen with the pivot comprising a recessed 12BA T nut.  The head will be flush with the bottom of the bogie, once ride heights etc. have been finalised.

The guard irons are very small, but quite a critical visual part of the bogie. The spring detail is probably just sufficient to give the impression of its function. 


Tim