Aveling & Porter (amongst others) built several small shunting / tram locos based on their traction engines. They were basically traction engines with flanged wheels and no steering. Their advantages were that they were cheap to manufacture (and to design in the first place) and they could be operated with minimal training by someone who was familiar with traction engines.
There are a few of these wonderful machines still in existence, the most famous probably being the "Blue Circle" engine based at the Battlefield Railway in Leicestershire. I have long admired these engines for their charm and simplicity, and for the fact that I like to think I could probably drive one myself without much difficulty. As far as I know, nobody has made any toy versions before now, so I decided to rectify that omission.
Like the originals, my version will be based on an existing traction engine - the Mamod TE1A. I have most of the parts required in my spares box. After some searching, I eventually acquired a set of 3.5" gauge wheels from a Hornby "Rocket", which are just about the right size. The small ones already fit onto a Meccano axle. I have fitted bushes on the large ones to fit.
As it happens, the Mamod firebox is just about the right width so that I can maintain the 3.5" gauge. There are several possible alternatives for the drive:
* pulleys and belts, as per the original Mamod
* gear train as per the original Blue Circle
* sprockets and chain, as seen on some other A&P examples.
I am experimenting with all three possibilities but the most likely is pulleys and belt, this being the simplest. Whichever option I end up with, it will probably be made using Meccano parts. The traditional direct belt drive from crankshaft to wheel, as found on the Mamod and others, gives an unrealistically high speed and not much pulling power. To reduce the speed and increase the tractive effort, I intend utilising an intermediate shaft, again using Meccano parts. Increasing the tractive effort might preclude the use of pulleys for the final drive because of slippage, in which case, I might have to use the sprocket and chain option.
There is already a gear built into each large wheel which is (not surprising for Hornby) the same pitch as Meccano. Unfortunately, it's too small to be of much help for speed reduction. A 3" Meccano gear would be more suitable if I chose that option, but, in either case, there is not much room anywhere for the small gear to mesh with it.
Another option I have to decide on is whether I will use the long boiler as originally fitted to the Mamod TE1A, or to use the shorter boiler from an SR1. I get the impression that the long boiler would be closer to the original in proportion but the short boiler would look better. I have both boilers available and can choose between them at a later stage.
The front wheels will need a rigid chassis, which will have to be made up from scratch, although I might, again, use the ubiquitous Meccano. For aesthetics, I will probably devise a dummy well tank, as per Blue Circle, which would also help to conceal the Meccano. Buffer beams will also be needed with suitably scaled buffers and draw hooks. These will have to be found somewhere.
Here's the progress so far. The back end is more or less finished; that is, finished apart from the finishing, if you get my meaning.
It's made up from Meccano and assorted Mamod parts from my spares box. I'm not sure if they'll all work together but I'm sure they can be made to do so. Here is a photo with the right hand wheel off, showing the large Meccano pulley and a couple of minor mods to the firebox:
The sharp eyed amongst you may notice I had to shave off a bit of the metal around the bottom edge. I found that, with the wheels set for 3.5" gauge, the pulley was pushed hard against the firebox. I also slightly flattened the pulley rim with a small hammer. The next photo shows just how close it is:
Because the Meccano axle is smaller diameter than the original Mamod one, I have fitted a couple of brass bushes to the firebox sides (attached to the inside so they are not visible). This also gives somewhat better bearing surfaces. This is important because the new wheels are both attached to the axle so that it rotates in the bearings. (The original Mamod wheels were free to turn on the axle, which probably remained stationary most of the time.) I realised, after I had done this, that the firebox sides are slightly tapered so that the holes in the two bushes didn't line up with each other. This meant that I had to do a bit of metal bashing to line them up.
Also, to improve rigidity, I've added some extra fixing screws between the two halves of the firebox. This, added to the fact that I've utilised two of the other fixing screws to mount the second shaft, means that it's now a bit of a hassle to disassemble the firebox. I hope I don't need to do that too often now.
I've decided to try it with all belt drive to start with and see how it goes. The other options, I've worked out, will need more clearance than I have without a re-think. I've also decided to use the long boiler, being closer in proportion to the oruginal.
I decided to get something down on paper (electronic paper, anyway) so I can get some idea of proportions and of the shape and dimensions of the chassis (please ignore the error in position of the rear axle. That was just a slip of the mouse!):
From this I extracted the outline of the frames for the chassis:
From this, I'll now have to work out how to make it. It doesn't lend itself to easy construction in Meccano so it looks as if I'll have to cut them out of sheet metal.
I cut the frames using a hacksaw blade in a power jigsaw, and 3 files of varying coarseness. I actually had to restart the second one because I made a balls-up of it by making a cut on the wrong side of the marked line. I rather regretted choosing 1mm thick steel while I was doing it but I'm glad I did now that it's done. They are nice and rigid.
And here they are attached to the firebox, using countersunk screws in the convenient holes already there for the SW1 chassis:
At this stage, I thought I'd get all the parts I have so far together to see how it's beginning to look ...
... and that's how I discovered I'd miss-measured something when I was calculating the length of the frames. This means that it will be impossible to get the scuttle in and out once the rear buffer beam is in position.
I'm not going to go through the process of cutting new frames again so I'll just have to extend them a bit. It just goes to show - even making a drawing beforehand doesn't guarantee you get it right!
Some of you may have seen the A&P Look-alike at the Steam Toy Lincs exhibition at Lincoln. I hadn't progressed much from the previous photos so I didn't bother to write anything up. I think the only progress I'd made had been to add the buffer beams. I don't have any buffers or draw hooks yet but I've temporarily fitted "dumb" buffers to give some idea. These are similar to ones found on some of the original A&Ps so it doesn't look too bad. The whole thing looked more complete than it was because I'd pushed the boiler into it's hole in the firebox to give an impression of proportions.
I mentioned in part 4 that I'd made a mistake in measurement and that I'd have to extend the frames to accommodate removal and insertion of the scuttle. On second thoughts, thereís no reason why the whole scuttle needs to be removable. In fact, the only thing that must be removable is the burner. That needs some means of attaching it to the fire box but the rest of the scuttle can be fixed, and is probably better like that. Therefore, plan B was to cut a scuttle in half and fix the top half to the frames, turned round so that it looks a bit like the bunker on the original. The burner is attached to the bottom bit, screwed in place with the handle removed - like the early SR1. The burner is actually a third party replacement, designed for use with the TE1 but slightly larger than the original.
However, I did discover another slight error when I fitted the wheels and put it on some track. The whole thing sloped slightly down at the nose, so I did have to redrill a couple of holes to line things up better. At the same time, I took the opportunity to fix the frames a bit more rigidly to the firebox near the bottom. There's one more bracket still to be made which will attach the frames to the bottom of the smokebox. To avoid further measurement errors, I'll leave that until I have the boiler properly fixed in the firebox.
I've made a major design change to the drive arrangement. Instead of having a second shaft on top of the firebox, I've now utilised a double pulley (from a Mamod SW1) mounted on the side. This looks a lot better, especially if I paint the pulley the same colour as the frame so it doesn't stand out. It will probably work better as well due to less friction. I had to move the final pulley to the other side, which entailed making the same "adjustment" to the clearances on that side.
I think we're almost there now. Apart from the one last bracket mentioned above, and the buffers and draw hooks, I think I have all the parts made. It'll soon be time to put it all together and see if it works. I'll be surprised if it does work first time because the piston, cylinder and port face all come from different engines of different ages. We'll see.
Not much new to show at the moment. The engine runs, but not well. I've been trying to get the engine to run smoothly but I have problems with priming.
* I've trimmed the boiler end of the steam pipe so that it only just pokes through into the boiler.
* I've washed out the boiler with meths and with lots of water.
* I replaced the old worn cylinder / piston with a brand new one.
* I tried putting the safety valve at the firebox end with a plug in the centre hole next to the steam pipe. That had no effect atall so I've put it back as it was.
None of the above made any real significant improvement. Filling the boiler to just over half way does help but it still primes a bit. There's a video clip if it running on blocks on You Tube (the speed is quite deceptive because of the "wagon wheel effect")...
... and here it is running on a short length of track, just to prove it can:
I can't think of anything else I can do to stop it priming so I'm just hoping that running in will cure it. BTW, I'm still looking for suitable buffers and draw hooks at a reasonable price. Next step will be cleaning, stripping and painting.
I've been busy with the paint brush and spray can:
... including a rather fetching deep blue VHT paint:
I was expecting this to be much brighter, which would have been ok but this is even better. A reminder, though, not to rely on the colour on the cap!
I just had to see what it looked like all back together again, even though itís not yet finished:
I quite like it, actually.
During reassembly, I made further adjustments to the screw holes in the frames and front bracket so that the boiler now slopes upwards, slightly, at the front. This, I hope, will help prevent the priming problem mentioned above.
I'm now thinking about finishing touches. Lining out, maybe? Someone has suggested boiler bands and I rather like that idea. I'm not sure if brass or stainless steel would look better (SS would be a better match for the existing band between boiler and smokebox).
Well, this is what it looks like in, what I think will be, it's final form, with the completed buffer beams and boiler bands:
The buffer beams are now wood, backed with the old metal ones for strength. By luck, I just happened to find a couple of suitable threaded hooks, to which I added short bits of clock chain. The buffers themselves are made up from mirror fixings and mains plug pins (the old fashioned 15amp round pin variety - how many of you remember those?). The boiler bands were cut from a tin can; not a perfect match for the mazak one on the smokebox but closer than the ready made brass ones would be.
A word of warning - the more observant of you may have noticed that the firebox is now all black whereas it was half blue in the earlier photos. This was not deliberate! It happened within 30 seconds on the first firing after painting. There was no blistering or any deterioration of the finish, just the total disappearance of colour! This is something to remember for the future. The paint was VHT brand and was cured for 3 days at around 100C. Maybe, if I'd baked it at a higher temperature, it might have survived better, but I'm not sure. Anyway, it looks ok so Iíll leave it.
And finally, for comparison, here it is sitting next to the Hornby Rocket (same gauge) ...
... and the Mamod TE1: