Building a NSWGR CPH Railmotor

[Deeja]

I am dedicated steam man, however there are times when steam is too much effort (Like loading all the ancillary equipment, tools, blower, coal etc) into the car when on holidays, or when you can’t run steam (total fire ban days), so I decided I want an electric or liquid fuelled motor 'play thing'. A number of design 'rules': It shouldn’t be too large, be as self-contained as possible, be able to run on fire ban days, be a proper scale model of something – not just a powered box, and preferably not too many compound curves, which ruled out some diesel models which have compound ‘cheek bones’ or hoods at the ends – I didn’t think my sheet metal skills were up to that, and do not have many woodworking tools apart from hand tools. So it was decided, after much scouring of photos, plans and thoughts of “How on earth would I make this or that” when looking at photos etc.

So it was decided that a NSW railways CPH railmotor would fit the bill. These are from the 1920s – definitely the steam era – and 42ft long, seemed just right for a 5"g model. Plus there are still quite a number preserved on heritage railways, museums etc, so access to a real full size one is possible if needed. They also have a certain charm about them.

See photo of prototype below


So I set to work during COVID lockdown and started sketching in CAD what to do. I obtained some 24V/150W motors which are small enough to axle hang yet big and powerful enough to handle the railmotor + 1 driver load. It is not a locomotive in the traditional sense and doesn't need to haul a great load. The prototype only had 1 axle powered so I reasoned 1 powered bogie is sufficient. Having axle hung motors also leaves the interior available for batteries, controller, electric vacuum pump, radio control gear (at a later date), on board battery charger, etc.

The basic design is a chassis as close as possible to the original's steel truss frame, and to make a skeleton from 6mm square steel and have a laser cut wooden body skin from plywood as the outer shell. I drew both the steelwork and wooden body panels at the same time as it is surprising how closely they inter react. I have used laser cut and scribed ply previously to make some covered wagons – see photo below.



Last week the steel parts arrived from the laser cutter for various body parts, bogies, drive train etc, and I now have enough to keep me busy for many months! The body panels will be ordered later when the main superstructure is more advanced. After all it is almost the last thing required, and also the most visible on the finished model, and as we all know the detailing is what takes a lot of the time.

This is not intended to be a quick ‘get me running a quickly as possible’ build, but to build a scale electrically powered model, and is expected to take quite a few months. I will post updates as I make progress, but do not expect an overly quick time scale. I would also welcome any comments and questions you may have. I know there are quite a few here on Oz, but I look forward to comments/suggestions from you UK based modellers.

Now back to the workshop to do some more.

[peteh]

I assuime you have also looked at Jim's build ? modeleng.proboards.com/thread/13762/building-nswgr-railmotor-401

[Deeja]

Yes I have. I decided I didn't want an all wood body as I wanted to be able to sit ON (with suitable seat) as an option so had to be strong enough. Intend to use a 1-bum truck with foot pegs on the railmotor. As as I said I have next to no woodworking equipment. But that is an interesting build nonetheless.

[Jim]

The CPH will be an interesting model and a nice addition to the growing number of non steam models.

Like you I decided that much as I love the Britannia I needed something that could be easily transported by a less than energetic senior cit while at the same time giving me lots of fun on the track.

Jim

[Deeja]

One of things about the CPH is that the body ends are square in the middle and angled on either side. From the drawings this angle calculates to 15.25°. I used 6mm for the headstocks and wondered how I could bend, accurately, the side bits to precisely this amount. Firstly I made a triangular 'jig' from 3mm sheet using Pythagorus to get an accurate angle. I then carefully hacksawed part way through the headstock to about 3mm deep square across where the bend was needed. I then bent them in the vice while heating with the propane torch until they were 'soft' enough to easily bend, and of course they bent only on the cut line. I got them as close as I could while trying not to burn fingers, and when cold gently tapped them to final position using a straight edge and the jig. When all done I TIG welded the back to fill up the saw cut and regain full thickness, and cleaned up the weld by filing. See photo. Note the black tape is only to hold things in place for the photo. When lined up against some of the laser cut parts with the same angle, I managed to get the ends within 0.2mm and was quite happy with that.



I also used the same jig for lining up to cut the ends of the buffers to the same 15.25° - the only way the buffers can be straight. Only the rectangular base is yet to be soldered on before buffers ready for painting.

[Deeja]

A bit more progress has been made on the CPH over the Christmas period. Sometimes slow due to the warmer humid weather 'down under', and it is 'holiday season'.

I have drilled and machined where necessary parts of the main frame and welded a lot of the bits together.



Starting to look like a chassis now!
It has been all TIG welded and the thicker cross beams will support the batteries, and provide some rigidity to the frame. The rounded parts of the chassis visible under and near the end of the photo are for clearance over the traction motors and transmission. The chamfered ends of the cross beams are weld prep ready for the side frames. These aren't on yet as there was shortage in the under bench store of the correct size, plus being in a holiday period and COVID restricting movements, the trip to the steel merchant hasn't occurred yet. On the smaller side sub-beams, I put tabs to slot into the 6mm sq holes in the main frame (also 6mm thick), but made the tabs 7.5mm long so they protruded 1.5mm on the inside which I then fused to the main frame. These sub-beams are also welded to the main frame top and bottom as well as the inner end. The side frames will be added as soon as possible. I also tapped a number of holes in these sub-beams to attach the various under floor bits like (dummy) battery boxes, air tanks, plumbing, foot rest mounts etc later. Easier to do it when they are separate bits of metal(!) even if some of the holes are never used.

The buffers have also been completed, and prototype buffer for comparison

and now already to fit.

Work has also been continuing on various other bits and below is a test partial fitment of the bogie side frames and horn blocks. More work to go yet but getting there.