Copenhagen Fields

[65179]

12 hours ago, CF MRC said:

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)

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. 

Once the spokes were in position a minute drop of very 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. 

The wheels were then given a coat of NER green: they are looking a bit vulgar in this photo. They will hopefully look better when the rims and hub are black. 

 

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

 

Tim

 

 

 

 

Avert your eyes now all you purists:

 

 

Less conspicuous in mucky black?

 

I realised some time ago that I'm not going to get everything I'd like to build done in my lifetime using the available wheels let alone altering them all.

 

Builders of MR, LMS and GC locos will be very busy with the piercing saw and the polystyrene given the latest version of the 8.5mm tender wheel has only 10 spokes 😉

 

Happy New Year everyone!

 

Simon

Edited January 3, 2023 by 65179

[Caley Jim]

If you speak very nicely to the wheel centre designer, I'm sure correct wheels could be provided. As far as I understand it's just a matter of changing one parameter in the CAD file. 

Jim 

[CF MRC]

I’m not quite sure the new type 5 wheel manufacturing process is ideal for small diameters (<7mm) as the 3DP stainless steel is a bit heavy around the hub and rim.

However, they were just right for the large driving wheels on the Skittle Alley as these locos had thick tyres  (I did trim the spokes a bit though). 
 

Tim

 

Edited January 3, 2023 by CF MRC

[queensquare]

1 hour ago, Nick Mitchell said:

 

Tony Wright observed that the pony wheels of my 9F had the wrong number of spokes - it nearly cost me the Groves Trophy in 2019!

At least it’s the correct gauge!

 

Jerry

[bécasse]

2 hours ago, Nick Mitchell said:

 

Tony Wright observed that the pony wheels of my 9F had the wrong number of spokes - it nearly cost me the Groves Trophy in 2019!

You just have to persuade him that, unnoticed by the average enthusiast, a few locos of the class had a non-standard number of spokes and it was one of those that you had modelled. Regrettably you hadn't brought the photographic proof with you!

[CF MRC]

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

Tim

Edited January 3, 2023 by CF MRC

[Caley Jim]

On our fortnightly group Zoom meeting this evening I mentioned to Nigel your issue with the bogie wheels.  A file already exists for 12 spoke 3ft diameter bogie wheels.  All the chief shopkeeper has to do is order them!

 

Jim

[CF MRC]

I’m not sure that there would be room for two more spokes Jim, if the size is maintained as is. From a conversation I had with Alan Smith, I think there are limitations on the stainless steel 3DP resolution. I also suspect the demand for the 12 spoke wheels would be a bit feeble.

 

Tim

[Chris Higgs]

22 hours ago, CF MRC said:

I’m not sure that there would be room for two more spokes Jim, if the size is maintained as is. From a conversation I had with Alan Smith, I think there are limitations on the stainless steel 3DP resolution. I also suspect the demand for the 12 spoke wheels would be a bit feeble.

 

Tim

 

Sounds like something that could be made as a one off limited run. There are a number of other wheel types that a single batch might be justifiable, but not as a permanently available item. I can also imagine someone of your experience Tim could machine up your own wheels from the 3D printed centres. The size of these prints is pretty small so a very small batch size is possible.

 

There are indeed limits on minimum thickness that can be printed that are higher on these metal materials than can be achieved with plastic.

 

Chris

[Nigelcliffe]

Minimum batch for the stainless wheels is one sprue, which is 25 wheels for small bogie wheels, 16 for larger bogie wheels and 9 for larger driving wheels.  Can be a mixtured set of sizes if wanting a sprue for a single loco (someone has to do the CAD).   
Thereafter is the cost of handling one sprue, which requires a conversation with the shop keepers - clearly its cheaper if the machining is setup to do a run of identical sprues than a one-off.  

 

I've pushed the 3D print spoke/hub wall thicknesses as far as I can with the supplier.   The designs get tweaked as things are learned - most now have the spokes sweeping up towards the hub rather than a step, and the crankpin is being changed to help the machining steps (new parts about to get into shops).  If someone can offer alternative suppliers, they'll get investigated. And if someone knows what they're doing with CAD they'll do a better job than me (self-taught make it up as I go along). 

 

Resin 3D printing (in domestic/hobby) machines will give finer spokes if someone wants to setup to do it, some of the "engineering" or "abs" resins are likely to give good results.  Downside of resin is that it's non-conductive, so designs need shorting strips adding for split-frame pickup.  

 

Each spoked wheel done for the shop has been a compromise -  how many spokes, which railway, crank-in-line?  etc..    I've done them by quickly trawling prototype lists where I can find them.  And a mix of railway companies.   If wanting exact spoke count, then ask for a single sprue to be done (and expect a higher price for the one-off).   

 

A 12 spoke 8.5mm bogie/tender wheel, with beval rim (intended for Black 5, because the old type wheels have sold out), is in the shop ordering process, image from CAD below.   CAD for a different beval, or no beval, would be very quick to produce.  

 

[CF MRC]

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. 

The test track was actually a section lifted from Chiltern Green forty 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

 

 

Edited January 6, 2023 by CF MRC

[Chris Higgs]

Hi Tim,

 

What is the reasoning behind making the loco a 2-2-6-2? Following your advice on 0-4-4s I made my chassis kits so they could (as an option) be built as an 0-4-2-2, which helps a lot with weight balancing issues, but had not thought about it on something more conventional like a 4-6-2. With this arrangement you seem to have a rather long rigid wheelbase.

 

Sorry if I missed this somewhere higher up in the thread.

 

Chris 

[73c]

Think your find that's a 4-6-2 @Chris Higgs

[Sithlord75]

The block has one axle, the next axle isn’t in the block, then the 3 drivers and the trailing axle - so I can see where @Chris Higgs is coming from. 

[CF MRC]

The reason for this arrangement is the proximity of the slide bars to the rear bogie wheel.

On a 4-6-0 there is less of a problem with using a conventional bogie because the overall wheelbase isn’t very long. However, on a pacific the trailing wheels cause an issue in terms of swing at the rear end. That is why Hornby have flange-less Cartazzi / trailing trucks on their pacifics.

The coupled wheelbase on a pacific is usually quite short and adding the rear wheel of the bogie doesn’t make the wheelbase unmanageable.  If it were on a bogie it would very likely kick into the cylinders and slide bars on a tight curve so they would have to be wider or chewed out at this point.  Having that rear wheel horizontally restrained make life simpler - it is what Denys Brownlee did on his Flying Scotsman and I had to do on my Stirling 8’ single - which has virtually no clearance at the front end on the prototype! The front pony on the Skittle Alley  can steer round a curve more easily than a bogie would do: the frames will be quite vestigial at the front to allow this to happen. 
 

Hope that long winded explanation helps to explain the rationale?

 

Tim

[65179]

As you say Tim you can get away with it with a 4-6-0. My B16 just has a fixed pivot for the front bogie with the bogie itself having a slot with a very gentle arc for this to move in. It just about goes around 2ft curves. However the restriction is due to there being very little side play for the coupled wheels not the bogie wheels catching on the slidebars/crossheads. If I built another I'd move the splashers out 0.5mm to allow a little more play.

 

Simon

[Chris Higgs]

2 hours ago, 73c said:

Think your find that's a 4-6-2 @Chris Higgs

 

Not the way Tim has built it. Similarly the W1 was often classified as a 4-6-2-2 rather than 4-6-4, as the rear traling wheels formed two independent truacks, rather than a bogie.

 

Chris

[Jol Wilkinson]

By moving the front bogie pivot aft you can alter the amount the front and bogie wheels move compared to each other. The further aft the pivot point is towards the rear axle the less it moves in relation to the front axle.

 

Hornby Dublo Pacific's had, IIRC, a pivoted arm fixed to the chassis behind the bogie. This link was loosely rivetted to the centre point of the bogie. The bogie swung from side to side on this link and also pivoted about it's centre. Presumably that's what  helped them around 15" radius curves at TGV speed.

[Chris Higgs]

59 minutes ago, CF MRC said:

The reason for this arrangement is the proximity of the slide bars to the rear bogie wheel.

On a 4-6-0 there is less of a problem with using a conventional bogie because the overall wheelbase isn’t very long. However, on a pacific the trailing wheels cause an issue in terms of swing at the rear end. That is why Hornby have flange-less Cartazzi / trailing trucks on their pacifics.

The coupled wheelbase on a pacific is usually quite short and adding the rear wheel of the bogie doesn’t make the wheelbase unmanageable.  If it were on a bogie it would very likely kick into the cylinders and slide bars on a tight curve so they would have to be wider or chewed out at this point.  Having that rear wheel horizontally restrained make life simpler - it is what Denys Brownlee did on his Flying Scotsman and I had to do on my Stirling 8’ single - which has virtually no clearance at the front end on the prototype! The front pony on the Skittle Alley  can steer round a curve more easily than a bogie would do: the frames will be quite vestigial at the front to allow this to happen. 
 

Hope that long winded explanation helps to explain the rationale?

 

Tim

 

Ah, I see now. GWR 2-cylinder 4-6-0s have a similar issue. As mentioned by others, this is often addressed by pivoting the bogie somewhere nearer or even over the rear bogie axle. However, only fixing it in the frame as you have done really prevents any lateral movement.

 

Chris

 

[Jol Wilkinson]

1 minute ago, Chris Higgs said:

 

Ah, I see now. GWR 2-cylinder 4-6-0s have a similar issue. As mentioned by others, this is often addressed by pivoting the bogie somewhere nearer or even over the rear bogie axle. However, only fixing it in the frame as you have done really prevents any lateral movement.

 

Chris

 

Chris,

that's what the HD arrangement avoided.

 

You can put the frames pivot point aft but still have a radial slot in the bogie. That way the bogie rotation is altered towards the rear but it still has lateral  movement.

 

Jol

[t-b-g]

There is an outside framed 4-4-0 that has been running on Buckingham for many decades which has a similar arrangement and is really a 2-2-4-0. The leading bogie wheels are on a pivoted pony truck and the rear bogie wheels are lightly sprung in a slot in the main frames with a small amount of sideplay.

 

That allows it to go around 2ft radius curves with no problems.

 

It is practical, pragmatic and it works.

[CF MRC]

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

[CF MRC]

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. 

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. 

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 (vice TBG and Peter Denny).
 

Tim

 

Edited January 7, 2023 by CF MRC

[CF MRC]

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. 

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

Edited January 10, 2023 by CF MRC

[Caley Jim]

There's nothing quite like the satisfaction of seeing a new chassis running for the first time, no matter how many you've made! In my case the thought is "I've got away with it yet again!". In Tim's case smooth running is only to be expected. 

 

Jim