Having worked on repairing my Lister thoughts have turned to building a new locomotive for Fen End Pit. I'd rather taken a fancy to the tiny battery electric locomotives built by the likes of Wingrove and Rogers and I thought that one of these engines might be worth trying to 3D print. A recent video in the 'Lawrie goes Loco' series on Youtube also rather drove my project along.
There are some superb plans available on Flickr from J. Tilston. I purchased a number of his drawings on CD which used to be sold under the 'Industrial Narrow Gauge Illustrated' name back in the early 2000's. I tried to contact the email address a few weeks back to see if any more were ever produced but have got no reply. Does anyone know what happened to them?
The drawings allowed my to produce a, hopefully reasonably accurate, 3D model of the loco broken down into parts which I thought I could print on my resin Phrozen Sonic Mini 4K.
To give you some idea of the diminutive size of this little critter the 'footplate' was designed to fold up reducing the total length of the locomotive to four feet so it could be lowered down a mine shaft. The wheelbase is the same as a gauge, 32mm in my 16mm:1' scale. The wheels match the diameter of O gauge lowmac wheels. The first attempt to print all the bits took just under 3 hours and came out pretty well - the seat failed to print because I had not really got the supports right and some minor changes were made to the model to sort out the fit and clearances.
I painted the battery box from this batch of printing as it came out well enough to use. I'll probably make some spares of this part and also the slightly different version with a 'peaked roof'. The main chassis is printed in a single part and includes recesses into which four 'High Level' etched hornblock guides can be installed. These were fitted after the assembly of the coupling rods and jigged using the 'rod with a taper on each end' jigs for 1/8" axles I use for Scalefour locomotive construction. I'm still undecided as to whether I'm going to need to work out a method of springing the axles or adding a compensation beam on the front axle or whether this will be unnecessary.
The O Gauge lowmac wheels obviously don't have crank pins for coupling rods and are also rather skinny so I tried printing some overlays to go on the front of the wheels. These included a 1.75mm hole in the centre for the end of the axle and a hole into which an Alan Gibson crank pin bolt would self-tap. The actual front edge of the wheel overhangs the rail by quite a margin so I'm hoping I can stick the overlay in place, fill the gap between the overlay and the wheel itself and get away with it!
The rods are just held in place by some wire insulation at the moment.
I've 3D printed the coupling rods and bushed the holes in them with some brass tube. I suspect that in the end I might resort to getting these etched though. They are surprisingly strong in resin but I think metal would be a better choice for long term use.
Ultimately the crank pin bolts will be cut short, proper crank pin nuts installed and then the crank pin covers stuck over them. These covers printed rather well given that they are only about 6mm in diameter, you can see the bolts and the grease nipple quite clearly. Again, for this test I just used a .05mm layer height, I will probably reprint at .03 for the final version.
The wheels (or more accurately the overlays) were quartered by eye and the loco seems to roll along quite happily without binding. The plan for motorizing is to try an N20 type motor for the first time, I've got a pair of the '100 rpm' versions but I'm waiting on a slow boat from China for some bevel gears. The motor is intended to sit in a cradle built into the chassis and there is a cover which will (hopefully) hide the gears from Fen End Pit's sand and make the unit look more like the actual motor which was installed between the frames. (Picture below was version 1) of the frame print before some minor tweaks were added.
Work on this project will probably pause now until the bevel gears arrive but I'm happy with the progress so far. I am still working on how to manage the power pick up as this locomotive will be powered from the rails as per the rest of Fen End Pit's locomotives. Fitting a DCC chip and stay-alive won't be an issue was the battery box is a very convenient space for them. I'm tempted to try and work out how to split the axles, I think I need to work out how to make some 1/8" internal diameter plastic 'muffs' to go around the axles. This would allow me to just connect some wires to the horn-guides and add some Brassmaster's shorting etches to the back of the wheels.
For now, here are some pictures of the parts, loosely assembled into the shape of the completed locomotive.
I will admit that I am really rather looking forward to seeing if I can actually make this run. I'm sure it will involve more work and printing - I can see the parts which don't make it being added the end of the Fen End Pit scrap siding, slowly disappearing under the undergrowth...