This week I have another new replacement part to share with you. A locomotive was brought in to get DCC sound fitted and I know from experience there’s a good chance certain parts will break when the locomotive is taken apart, and in this instance I was not mistaken. The Locomotive in question is a Gresly V2 made by Bachmann under their Branch Line range.
These locomotives are very good, although now an older model, and are normally very reliable. The primary problem these, and other locos in the range, suffer from is split axels and I’ve already 3D printed parts to repair them, which you can read about here.
However, the axels on this locomotive are fine; the issue is with the split chassis fasteners. A lot, if not all, of the Bachmann locomotives of this generation, have a split chassis. This means the chassis is in two halves with each side conducting power from the wheels to the motor, eliminating the need for wires. For DC operation this is perfect. But for DCC I need to separate the chassis halves to electrically isolate the motor. The chassis halves need to be screwed together but electrically separated. This is achieved by using a plastic chassis fastener, plastic washer and metal screw. The fastener has a square head that fits into a square recess in the left chassis half to stop it rotating. The washer fits between the chassis halves, over the fastener to separate them, and the screw pulls the parts together as it bites into the fastener.
The problem comes, as with this V2, when the locomotive has never been taken apart and the plastic fastener has either deteriorated or maybe shrunk. I’m not sure what actually happens. But the screws are very tight and the force needed to get it to move is often more than the fastener can take and the tube section twists off the square head; as you can see below.
Or the tube section simply breaks at the end of the screw, which also happened on this locomotive.
It is possible, if you’re both careful and lucky, to glue the parts back together, but more times than not it doesn’t work and I often come across these locos with several missing fasteners.
So my solution, as is my way, is to 3D print replacement parts. I designed the fastener to be a direct replacement and included a washer as sometimes the originals can get lost. They are 3D printed in Shapeways Fine Detail Plastic as it’s the most accurate.
Before these can be used it’s very important to clean out the tube section. This is because it will be full of 3D print residue which, if left inside, will add pressure to the tube wall as the screw is driven in, cracking the tube. To clean out the tube I use a 1.26mm (0.049″) drill in a pin vice. This won’t actually remove any of the tube material, just ream out the hole, as you can see below.
There’s usually a lot of residue in the hole because it’s small and Shapeways post-cleaning processes can’t get in there.
With the fasteners ready the chassis can be reassembled. The V2 uses five, as you can see below by the holes in the right side chassis half.
With both sides fitted you can see the square heads in the left side chassis half. It was only when I put this photo up I realized I had the front one in the wrong way round. Fortunately with that one it works from either side.
The square recess in the left chassis half has a bit of tolerance so the head will rotate a little.
This particular V2 is now back up and running and has an ESU sound DCC decoder, working lamps, and a realistic firebox flicker whenever the fireman opens the firebox door, which reflects nicely around the cab.
If you have another part, such as this fastener, which has broken and you can’t find a replacement I’d be happy to see if I can draw it up for 3D printing. You can get in touch via the contact page.