Cycling home from work through a hailstorm and icy rain today was rewarded by the arrival in the post of a 3D printed sample from Modelu. It is a 4mm 3D printed spring and axle box set for a Stanier brake van. This is something I've been thinking about for a while. One of my occasional projects is an etched brass brake van kit from Connoisseur Kits. Fairly straightforward etched brass stuff. I got to the stage where all I needed to complete it was to fit the axle box and spring castings. Now, the spring hangers, spring isolation rubbers and 4'6" leaf spring are distinctive on these Stanier vans. The white metal castings supplied with the kit are serviceable but a bit lumpy and don't really capture the character of the prototype. Geoff Kent shows a method for making these parts from plasticard in one of the Wild Swan 4mm Wagon books. I guess that's OK if you have Mr Kent's superhuman skills with polystyrene and a scalpel. I'm afraid I don't. You'd have to make 4 this way for a single van, and if you wanted more than one van... So the project was put in the 'difficult box' for a while.

I came across Modelu on RM Web a while ago and saw some of the 3D printed output on the website. Reasoned that this could be a way of making some really good parts in any quantity required. I e-mailed a query to Alan Butler (Mr Modelu) and he sent me a photo of some similar items that he'd printed. Seemed feasible - game on!

As it happened the prototype information wasn't too difficult to find. The axlebox looks like an LMS 10" x 5" ABW.52 type (corrections please if you know better!) and by sheer jammy luck there is a drawing of this in LMS Wagons Volume 2 (page 170). Not a full engineering drawing, but enough to model up the axle box from in sufficient detail for 4mm.

I couldn't find a drawing for the brake van spring and hangers directly , but standardisation on the LMS means that the same 4' 6" spring and hanger details are used on other stock. There are a few decent drawings of fitted stock using these parts in Official Drawings of LMS Wagons Volume 2. (In fact there is enough information in those 2 volumes to be able to work out the detail on almost any LMS or related early BR wagon if you can identify the standard parts used - I wish there was more information like this published). Again it isn't a full drawing but there's enough to scale from to model the parts on CAD.

A few evenings on the Mac gets you this solid model...

Exported as an STL and e-mailed to Modelu for review. Alan suggested a few tweaks to suit it to the printing process. The updated model was sent to Modelu and eventually here are the samples. I think you'll agree they're a huge improvement on the original castings.

Typically when I'm working on things like this I get so close to the detail that I miss bigger things. Comparing again with the prototype it is immediately obvious that I have undernourished isolation rubbers. I'll change the model again before I get some produced.

Very happy how this has turned out. For me this is almost a revolution. From now on anything I can obtain prototype data for I can model. Once the CAD model exists I can STL it to any scale I like. The process isn't magic and it does have some limitations, but it seems they're not difficult to design around. On Modelu's advice I've flattened the spring and rubbers on the back so they print nicely on the machine platen, and I've added some extra material around the hangers just to make them robust enough to handle. Bonus feature, by the way, I've made the axleboxes hollow so I don't have to scoop them out to fit over the axle bearings - hooray a tedious, hated job eliminated. I'm already thinking about some distinctive LNER wagon axleboxes in 7mm. Maybe an anchor mount tank for a 14 ton tank wagon in 2mm. Driving wheel centres for some of the more distinctive locomotive wheels that are not well represented by proprietary generic wheels? Could be a long wishlist.

Cost? The cost is derived from a fixed set up cost for a job and a charge based on the volume of resin used. Big solid things will be quite costly. Modelu will quote for the work when they've reviewed the model. For a few sets of small parts like this it doesn't cost too much. Probably what I'd expect to pay for castings, if they existed, but of significantly higher quality.