Late last week I had a delivery from Shapeways which contained the next iteration of the parts for the O14 Clayton battery electric loco I'm working on. This is now version three of the design and it looks like I've solved all the outstanding problems with the previous version.
The main differences are to the way the parts fit together. Firstly I've narrows the steel weight slightly (which involved changing the shape of the cutouts for the screws) so that it will fit inside the body without distorting the sides. In the previous design the two main parts of the model were mostly held together as a friction fit, but only along two small surfaces (the back and front of the top piece fit against the front buffer beam and the front of the driver area). In theory this was enough, but often the parts would warp ever so slightly during the printing process and although they would hold initially would spring apart just by sitting there. Also if viewed from low down there was a slight visible gap between the two parts above the wheels.
I've solved the problem by adding more material to both parts to increase the surface area of the interlocking sections. This means there is now a block on the bottom of the upper part that slots between two of the supports in the bottom half to keep the flat rear area flat. To make sure the front part stays together, and to get rid of the slight gap, I've extended the body sides upwards so that they fit inside the top half by a couple of mm. This seems to work so well that once the parts are together they require a fair amount of force to separate. Combined with the retaining screws it looks as if it will be a nice solid model once I've built it up.
Talking of building it, this model is going to be a little different to every other one I've built as once it's running it will be packed up and shipped off to it's new owner. When I was visiting ExpoNG I spent a very enjoyable evening drinking beer and talking railways with David John the builder of the wonderful O14 layout Rhyd. He was really taken with the first prototype of the Clayton and has asked me to build one to run on the quarry tramway. Normally I'd have waited and built up another print rather than what is in essence a prototype model, but as it is destined to be one of David's Christmas present I don't have time to order more parts. It will also be heading to David unpainted as I feel that my loco painting skills (wave an aerosol can at it) fall well below that of the other locos on the layout. Anyway David has kindly agreed that I can document the build and hopefully at some point there will be photos of it earning it's keep on Rhyd.