A few months ago at the NMRA (BR) convention in Bournemouth I was asked by a fellow modeller, Mike Dobson, if 3D printing could be used to produce some replacement gears for one of his O Gauge locomotives. In this post I will share with you how we achieved just that.
The locomotive in question is a Rivarossi O Gauge F9; although the test locomotive is a Red Caboose GP9 shell with a Rivarrossi F9 chassis in it. Below is a shot of the locomotive on Mike’s layout.
The gear which Mike wanted printed is the final gear in the transmission. This is the gear is on the locomotive axles. The original plastic gear had split, as you can see in the picture below, and no longer clamped onto the axle but simply spun in place. The gear is press fitted onto the metal axle and friction between the plastic and the metal means the axle will rotate with the gear. The plastic Rivarossi used for their gears is rather brittle and it’s a common problem for this to split like this.
The first thing to do was to measure and draw the gear in the 3D model. Below is a rendering of a pair of gears.
Then it was off to the printer and for these gears I used Shapeways Frosted Ultra Detail material, the first set is shown below. As well as being Shapeways highest detail material it is also one of the most accurate. And it has very similar properties to the original gear material although not so brittle, but mainly that it has a hard finish so should be long wearing. I felt that the White Strong & Flexible material, despite being cheaper, may lead to the gear teeth being uneven and also may wear down very quickly.
With the gears successfully printed it was time to try them out on the F9 chassis. Below you see the underside of the F9 with a new 3D printed gear on each chassis axle. As this was the first run of gears there was a bit of trial an error involved with the fit onto the axle. If the hole through the middle was too small then pushing the gear onto the axle will cause the gear to split. If the hole is too big there will not be enough friction to rotate the axle. With the first print I was slightly too big on the hole. This has now been corrected and the next set should be spot on. However the main test was to see how well the 3D printed gears stood up to the punishment of an O Scale motor so Mike friend and fellow O-scaler Steve Morris reamed out the gears and fitted a brass sleeve inside. The gear was now a tight fit onto the sleeve and the sleeve was a tight fit onto the axle.
Below are some close-ups of the gears in place and you can just make out the brass sleeve.
With the gears in place and the locomotive fully reassembled it was time for a test. As well as the nicely scened sections of Mike’s layout he also has a staging area above which is reached by a 2.5% curved grade. You can see this below along with Mike’s test train of six loaded ore cars, four box cars and a caboose. This grade also forms part of a continuous run so the test locomotive could be left to trundle round with its train for a few hours. This was a good check for wear on the gears, and after several hours there was none.
Here is video of the train running through the station and then up that curved grade.
The second set of gears with the correct hole size will be going to print soon and Mike will be doing some more tests with them. Once we know that they are correct I will make them available for everybody who needs replacement gears for their locomotive.
If you have similar gears on a locomotive that need to be replaced and would like to try a 3D printed replacement please contact me through the contact page or drop me an e-mail.