GWR Armstrong Class Loco

M

Mikemill

Western Thunderer
There are several handsome 4-4-0 loco designs from the 19th century but for my money the GWR Armstrong Class engines are more elegant than the others.

I built one of these engines years ago in G1, I think one should be represented in G3. As I have the drawings for G1 it is easy to scale them up to G3.

I started with the wheels, they are machined from 8mm ali plate.

MikeBrunel.jpgArmstrong2AB+W.jpgP1120979.JPG
 
AdamF

AdamF

Western Thunderer
Incredible! Wheel production is something I want to get into in time. Broadly how are these machined? Is it CNC milling?
 
M

Mikemill

Western Thunderer
Adam

The wheels were cut on a CNC mill, I have experimented with different ways to make a scale wheels. Several of my G1 locos have wheel centres milled from acrylic with steel tyres. The problem with larger G3 wheels and making steel tyres is the availability of machinable steel tube of the right diameter, I have not found any thus you end up carving tyres from 4in dia solid bar.

So, I thought why not machine a complete wheel from aluminium, given the amount of running a model engine would do the ware on the wheel would be very small, if any.


Mike
 
AdamF

AdamF

Western Thunderer
Mikemill said:
Adam

The wheels were cut on a CNC mill, I have experimented with different ways to make a scale wheels. Several of my G1 locos have wheel centres milled from acrylic with steel tyres. The problem with larger G3 wheels and making steel tyres is the availability of machinable steel tube of the right diameter, I have not found any thus you end up carving tyres from 4in dia solid bar.

So, I thought why not machine a complete wheel from aluminium, given the amount of running a model engine would do the ware on the wheel would be very small, if any.


Mike
Click to expand...
Thanks so much for confirming - the results are exquisite!

Looks like I need to learn CAD!
 
NickB

NickB

Western Thunderer
Having turned driving wheel tyres from the aforementioned 4in dia bar, I understand the problem. Next time, I thought to get some rings laser cut from steel sheet to use as blanks. That will reduce the volume of swarf by a huge percentage.

Nick
 
paratom

paratom

Western Thunderer
Mikemill said:
Nick

That's a very good idea, 3D printed wheels with laser cut steel tyres is the answer.

Mike
Click to expand...
That’s a great idea if your talking about 3D printing in metal. The trouble with standard 3D printing resin is it has a habit of changing shape sometimes over a period of time. Alan Harris would be impressed.
 
JimG

JimG

Western Thunderer
NickB said:
Having turned driving wheel tyres from the aforementioned 4in dia bar, I understand the problem. Next time, I thought to get some rings laser cut from steel sheet to use as blanks. That will reduce the volume of swarf by a huge percentage.
Click to expand...

I CNC cut my spoke centres from brass sheet - typically CZ120 from Ian Cobb. It isn't cheap but it is flat. Being a sheet, I can screw it down to a spoil board on the table to hold it in place while doing the CNC cutting. I keep the "holy" sheet left after wheel cutting to use the bits left to cut smaller items - like axleboxes, etc. There is a bit of waste, but worth it for the ease of holding down. And CZ120 brass is a lot easier on milling cutters. :)

CalLocoWheels-03.jpg

Tyres are from mild steel bar but I try to trepan larger tyres off the bar so that the centre of the bar is left for smaller, probably, carrying wheels.

Jim.
 
M

Mikemill

Western Thunderer
Jim

Good to see you to embrace the joys of CNC machining, we all work in our different ways, I think the point is by the time parts are painted who knows what material they are made from as long as they work and are durable.

Re 3D printed wheels, Nick and I have made wheels using 3D centres and steel tyres for a few years and to date they remain stable.

Mike
 
JimG

JimG

Western Thunderer
Mikemill said:
Re 3D printed wheels, Nick and I have made wheels using 3D centres and steel tyres for a few years and to date they remain stable.
Click to expand...

I've done that with wagon wheels in S scale and it worked quite well. The main problem I had was getting an acceptable TIR on the wheels until I discovered that that had mainly been caused by non-concentric journals on the commercially produced axles. :)

Jim.
 
paratom

paratom

Western Thunderer
JimG said:
I CNC cut my spoke centres from brass sheet - typically CZ120 from Ian Cobb. It isn't cheap but it is flat. Being a sheet, I can screw it down to a spoil board on the table to hold it in place while doing the CNC cutting. I keep the "holy" sheet left after wheel cutting to use the bits left to cut smaller items - like axleboxes, etc. There is a bit of waste, but worth it for the ease of holding down. And CZ120 brass is a lot easier on milling cutters. :)

View attachment 191360

Tyres are from mild steel bar but I try to trepan larger tyres off the bar so that the centre of the bar is left for smaller, probably, carrying wheels.

Jim.
Click to expand...
Do you heat shrink the steel tyres onto the wheels?
 
JimG

JimG

Western Thunderer
paratom said:
Do you heat shrink the steel tyres onto the wheels?
Click to expand...

No, I turned the tyres to be a push fit on the brass centres. Here's the thread from six years ago describing the process :-

1/32 - A Loco for the Garden

Thanks Jim I like Mach3 software I haven't tried cut2d before. I have a sherline based system but the Z axis isn't accurate it can drop suddenly due to the weight of the motor being attached to it. Richard
www.westernthunder.co.uk

However I think I remember that I got a wee bit of slippage between tyre and centre on at least one wheel when doing the tyre forming operation and I fitted two diametrically opposite 8BA pegs at the centre/tyre joint on the rear of each wheel to lock the tyre in position and all the remaining tyre forming operation was completed successfully. I could probably have applied about another half thou of interference to get a better press fit but I was using the Cowells to do the pressing and I was worried about its capability to apply heavy press fits. My ML10 in the garage would probably have been fine, or the big Record vice on the bench with a pipe extension on the handle. :) But I didn't think about heat shrinking and that could have worked well.

In my smaller scale - S - I've used an easy fit and very thin cyanoacrylate to wick into the joint between tyre and centre and that seems to have worked very well.

I also use split axle pickup so it is essential that there is a good electrical path between tyre and centre.

Jim.
 
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NickB

NickB

Western Thunderer
Just to add to MIke's comment about 3D printed wheel centres, they are done in PA-12 nylon by commercial printers. This material is considerably stronger and more durable than resin, in fact, it is very similar to the plastic that Slaters use for their wheel centres (except theirs is injection moulded rather than printed, the right choice for volume production). If you search here for the threads on Mike's Saint and my Precedent, you will see examples.

Nick
 
LarryG

LarryG

Western Thunderer
The 'red' looks a tad bright to me and something akin to the wrong shade that was applied to 'City of Truro'. I remember it led many a modeller astray for years. A darker and presumably more correct shade was applied in the 1970's restoration.

Notwithstanding the colour, this is a magnificent model from the handmade wheels up.
 
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