A few months ago at the 2014 NMRA(BR) winter meet in Benson, England, I had an unfortunate breakdown with one of my small steam engines.  Upon putting the engine on the track and turning up the power the engine stubbornly stood still even though the motor was spinning frantically.  After inspecting the engine it was obvious that the drive shaft was missing.  So in this post I wanted to share with you how I have fixed it.

The engine in question is an N Scale 2-8-0 steam engine made by Roundhouse (formally Model Die Casting).

These are great models and run like sewing machines.  Due to the size there is next to no room inside for big motors and drive parts so Roundhouse installed a small motor in the tender, they even managed to fit in a small brass fly wheel.  The motor connects to the locomotive via a drive shaft which protrudes from the tender into the back of the cab.  The drive shaft then turns a worm gear in the boiler which connects to gears on the axles, consequently driving the wheels.  Because the tender is hinged where it joins onto the back of the engine the drive shaft has to be flexible.  This has been done using a form of ball joint. The balls on the ends of the drive shaft press fit into sockets and are held in place by the springiness of the plastic sockets.  Normally this configuration would simply spin in the sockets but the balls on the end of the drive shaft has two spigots sticking out from each ball.  Each socket has slots corresponding to the spigots so when the drive shaft turns so does the socket while allowing for the movement of the tender.

The drive shaft is made form black plastic and is very small, measuring only 11.25mm long with a diameter of 0.7mm.  So not to be beaten I decided to 3D print a new one.  Luckily I have a another Roundhouse 2-8-0 so I was able to pop out the drive shaft, pictured below, and copy the dimensions.

This was s fairly simple model, the main concern was getting the length and diameters correct.

Then it was off to the printer and a week later I now have a replacement drive shaft.  I printed this in FUD but it should be printable in WS&F or BS&F as well.

After an overnight soak in Goo Gone and a wash off it was ready for a coat of paint.  Pictured below, the drive shaft on the left is the original, the one on the right has been painted.

I first test fitted an unpainted drive shaft, which was successful, then once the paint was dry I fitted the black painted one.  Make sure the pegs in the drive shaft line up with the slots in the socket before you push it in.  It takes a reasonable amount of force to push the ball into the socket and if the pegs are not lined up they will snap off.

And there you go, a repaired Roundhouse 2-8-0 with a 3D printed drive shaft.

If you too have been unlucky enough to loose your drive shaft from either a 2-6-0 or 2-8-0 by MRC/Roundhouse or even the newer Athearn ones you can get a replacement here.  I also do a set of two, just in-case you need a spare which you can get here.