In a similar post to last week I have another replacement gear to share with you.  This time it’s much larger and for a G Scale 0-4-0 Pennsylvania 20-Ton Diesel Locomotive; made by USA Trains.

Despite being a small locomotive it’s a big model, G scale has a model ration of 1:22.5, and is heavy.  This also means that the motor has lots of power and the transmission needs to be able to withstand the forces applied.

Both of the axles are powered from a worm gear on each end of the central motor. The worm gears drive plastic gears which also form the axles and isolates the two metal wheels from each other.  As you can see in the image below the plastic axle has split.  This means the motor drives the gear which turns but the gear doesn’t turn the wheels.

As replacement parts for this locomotive were not available I drew one exactly the same size as the original and 3D printed it in Shapeways Fine Detail Plastic, formally known as FUD.  As I’ve said in previous posts this material is ideal for gears as it’s hard-wearing.

The original gear was also a bit mangled as the softer plastic tends to get damaged by the metal worm gear when under heavy loads such as starting and stopping suddenly.  The new gear with the harder plastic can withstand this without being damaged.

The axles have grooved ends to enable them to grip the inside of the plastic axle.  With some evenly applied pressure they can be pushed into the new axle.  In the image below they need to be pushed in a bit further but you can see the grooves in the metal.

The locomotive motor is in the box between the axles and when the lid or base is screwed on the new gears are pressed up to the metal worm gears.  The motor box is not connected to the body but clamps to the axles which sit in sprung axle boxes.  This allows the locomotive to navigate bumpy track and gradient changes without losing traction.

Once the motor base is replaced the locomotive is ready to go back out onto the railroad.

The replacement drive gear can be found here.

They are also available in a pair here.

Next week I’ll have even more 3D printed gears to share with you but this time it will be for  N Scale.