Advice for Scratchbuilding in N: Chassis, Wheels and Drive

[mpeffers]

Hey guys,

Beyond the occasional building, I've not really considered myself capable of scratchbuilding anything to a particularly satisfactory degree - particularly not since dropping down a scale to N. However, I was recently introduced to Shapeways and suddenly the idea of creating my own bespoke model doesn't seem so out of reach. As a fourth year engineering student, I have had a reasonable amount of experience with 3D modelling software and the chance to combine my hobby with the exciting world of '3D Printing' seems too good to pass up.

 

Photo: Mike Barnsley, www.swindonsotherrailway.co.uk - 1336 at Cheltenham Leckhampton on a RCTS railtour.

 

The plan is to produce a model of the M&SWJR No.12 as rebuilt by the GWR as No.1336 and turned out in BR black as she ended her days as the final remaining M&SWJR loco. With a set of 7mm plans, I am reasonably confident I will be able to create the geometry to send to Shapeways and produce a reasonable body for the loco, I fear the ultimate success or failure of the project will most likely hinge on the chassis, wheels and motor - things I haven't had so much experience with. I particularly don't want to end up investing a lot of time and money into a model that is pretty but ultimately immobile. I have had a few ideas that I shall outline below, was hoping those here with far superior knowledge of these things could look them over and advise me how best to go forward.

 

Option 1: Dapol 14xx Chassis, Tender Drive

It may be due to a lack of imagination, but the 2-4-0 wheel formation immediately lead me to look into the Dapol 14xx. Below the running plate, the similarities between the two locos are promising. The overall wheelbases are almost idential: 15'7" for the M&SWJR loco and 15'6" for the 14xx. Unfortunately, the drivers are significantly closer together on the 14xx - 7'4" compared to 8' - but this may be visually offset to some extent by the 14xx having slightly smaller drivers - 5'2" compared to 5'6". The leading/trailing wheels are similar too - 3'8" for the 14xx, 3'6" for the M&SWJR loco - although the more exposed leading wheel would most likley mean the Dapol one would need replacing regardless.

I presume Dapol made use of the enclosed cab/water tank area to house the motor in the 14xx, space that won't exist when the chassis is reversed for the 2-4-0. The easiest way around this that has occured to me would be to remove the Dapol motor and hack off any other parts that otherwise wouldn't fit inside the new bodywork and instead use a powered tender to provde the drive (perhaps connecting the Dapol pickups on the loco to the tender to improve running). I have found details of readymade motorised tender chassis hard to come by, although using Union Mills' tenders seem a popular choice. A rather expensive option appears to be available from www.motorbogies.com also. The tender wheelbase is 12' and I hope the whole thing is tall enough to fit a motor and gears inside:

Photo: www.warwickshirerailways.co.uk - Sister engine 1335's Tender - big enough for a donor motorised chassis?

 

Option 2: Custom Engine Chassis, Engine Drive, Donor Unpowered Tender Chassis

Shapeways have begun producing parts in brass by '3D Printing' a mould and casting into it. Although I'm currently unsure of their tolerances, this could make it possible to convert a nice, precise 3D model of a chassis into rigid brass, complete with fittings to mount a motor so that everything lines up nicely with the driven axle etc. If I were to opt against tender drive, the next best location that occurs to me to mount the motor would be to angle it down through the firebox and onto the leading driver axle, taking advantage of the cover of the bottom of the boiler provided by the front splasher.

 

Photo: Neil Lambourn, www.swindonsotherrailway.co.uk - Side View of 1336 - room for a motor angled down through the firebox?

 

When I first considered this option, I had assumed it would be possible to purchase pairs of wheels and 8' connecting rods to suit any needs. Initial searches have not been promising. A donor locomotive might instead be necessary, but it would allow me to dive into the world of cheap spares/repairs. If I could find something suitable attached to a 12' wheelbase tender, that'd be grand.

 

Option 3: Custom Tender Chassis, Custom Tender Drive

Even if I can't find a readily produced motorised chassis that would fit within the confines of the tender, I'm convinced that I would be able to find a motor that would fit above the axles and could devise a system to transmit its torque to the tender wheels. Again, this would rely on Shapeways' brass being accurate enough to keep everything aligned.

 

Either a donor chassis, such as a Dapol 14xx, or another custom chassis from Shapeways could be used for the engine - as it would be unpowered, the design would be less critical.


At the moment, my preference is with Option 1 if only because I fear the tolerances required to get everything running smoothly in N gauge are presumably very small and it concerns me that my lack of experience in scratchbuilding chassis would ultimately leave me at the mercy of Shapeways' own tolerances - if anything was slightly out when the chassis reached me, it's unlikely I could rectify the problems. Using ready-made chassis at least means they will have already been rigorously tested to function on N gauge track, although the need for two donor locomotives may drive the price up a fair bit.

I'm very interested to know what other people think would be best, though. And any suggestions for suitable donor locomotives for any part - wheels, coupling rods, tender or loco chassis with appropriate wheel spacing - would also be greatly appreciated.

 

Thanks very much,

Matthew Peffers

[garethashenden]

How long have you been in N and how committed to it are you? This seems like a good 2mm project. You could use all the 2mm Association components and know-how to create a chassis to fit the 3D printed body. Usual practice is to stick the motor in the tender with a cardan shaft to a worm driving the drivers.

[mpeffers]

It's probably been two or three years now since I scaled down from 00 to N. The 2mm Scale Association webpage did feature in my searches for components, particularly wheels, but I'm lead to believe they are profiled for 2mm finescale and are incompatible with the Code 55 track I'm currently using. I guess other components would be more versatile though.

As for the cardan shaft system, I have encountered something similar with my Ixion Manor and I have had all sorts of problems with it.

[mpeffers]

In case anyone's interested, I ultimately went with a Union Mills tender chassis/motor and the Dapol 14xx chassis. I've attached a picture which will hopefully be visible. The motor and some of the plastic moulding has been removed from the 14xx chassis. A lot of the metal will also have to be removed, but I shall tackle that later.

I feel inclined to impart some of my experience here in case anyone stumbles across this topic looking to do something similar - if you take the motor off an N gauge Dapol 14xx chassis (or the old design at least), the driving wheels unfortunately do not roll freely. The connecting rods between the two wheelsets is either two long, has too much slack or a combination of the two. As expected, all works fine when the middle axle is driven, but the wheels started to jam quite severely once the motor was off.

To counter that, I had the probably slightly foolish idea of bowing the connecting rods out slightly to tighten them up. It was a rather frustrating process and in hindsight I probably should have put a bit more thought into other options. Nonetheless, and rather more by luck than judgement, the wheels have freed up a fair bit now and with a bit off added weight in the bodywork (I may opt to print it in brass) should at least keep the wheels rolling. On the down side, the connecting rods are now rather bent (although it's only really visible on very close inspection) and the chassis rocks from side to side a little. Probably, were I to attempt this again, I'd wait until I'd aquired the time, skills and tools to make my own chassis.

 

Still, she lives and I'm happy to press on to the next stage of the build - the bodywork. As I mentioned before, this will be largely a 3D printing process so I'll probably open a topic in the relevant forum sub-section in due course.

[Tricky-CRS]

Looking good, you could still use finer code 40 track in N Gauge using finetrax components.

[mpeffers]

Hi Richard,

Thanks for the compliment. I agree that the Code 55 does look a bit clunky, particularly after my recent trip to Warley and seeing some 2mm FS up close, but I don't think I'm ready to make the change just yet - not least because I've already spent a reasonable amount on the trackwork already and it's down, painted and functioning. Along with DCC, it's down on the my list as something for the future, once I've graduated from uni and am reasonably settled somewhere with a stable income.

 

Matt

[Kris]

Have a look at http://www.britishfinescale.com for further track options. 

[mallardsp126]

Hi just a couple of thoughts it may be possible to us the 14x chassis another way by removing the motor and adapting the worm drive so as it could be driven from the tender Dapol style I think nbrass do a kit for modding some farrish  tenders to drive the loco this enables quite a bit of weight to be added to improve drive hope this gives you some food for thought.

ps may be interested in acquiring the printed parts to make one for me

Geoff  

[mpeffers]

Hi Geoff,

It's something I considered, particularly when I was having trouble getting the wheels to turn. I think the main issue is that the 14xx chassis is turned around, so linking the tender to the worm on the driving axle would involve burrowing through a lot of the exisiting metalwork on the chassis. As you can just see in the photograph, one of the two screws holding the two sides of the chassis together is also located in the lump that would be coming off (I'm still not sure what I'll do about that when I start cutting the metal away - I'm inclined to keep the screw so I can still take the whole thing apart again if I need to. Might see if I can trim some off the end and bury the rest in the firebox.) I think, for those with the tools and expertise, a cardan shaft and a custom chassis would be the way forward. And yes, finescale too...

It might be a while yet before I've got the bodywork finalised and printed. Will be happy to share the files once they're done.

Matt