Earlier this year I shared with you my plans for my new N Scale Alco C-855. You can read parts one and two here and here. I have recently started to do more work on the project and have test printed the 3D printed parts which will extend the chassis for the new locomotive. In this post I will share with you how they came out.
As discussed in my previous posts the chosen chassis, as modeled below, for the C-855 is going to be Con-Cor’s 4500 Gas Turbine/GE U50 chassis.
This chassis needs to be extended, as shown below, because although the C-855 uses the same trucks they are spaced further apart.
The chassis needs to be extended by 10mm and ideally in the middle over the motor. To do this I have designed a complete replacement section that will extend the chassis and clamp the motor keeping it in the correct place. Below is a rendering of the new parts.
These have been designed to be printed in stainless steel. Although this metal is more expensive to get printed than plastics I didn’t want to reduce the weight of the chassis as this would have a negative effect on the locomotive’s tractive effort. As the C-855 chassis will be longer it should now be heavier which will hopefully add to the tractive effort. The C-855 did have 1000 more horsepower than the 4500 Gas Turbine and 500 more than the U50 after all.
The new extenders were printed by Shapeways and arrived ready to use as you can see below.
In close up shots like this you can see the layering effect caused by the 3D print process; this is more pronounced than on some other materials as the layer thickness is greater with stainless steel. Shapeways also offer this material polished which removes these lines but as the parts will not be visible once the locomotive is complete this did not seem necessary.
A small change to the parts from the rendered view above is the introduction of wire routes. This allows the bottom motor wire to run up between the shell and the chassis. For DC this is not necessary but for DCC the motor feed needs to be isolated from the chassis and a wire used to connect the motor to the DCC decoder.
Just to show that these really are metal, below is a photo of a basic volt meter set to measure continuity. One of the parts has been laid across the pins. As you can see the meter is reading 100%.
The parts will also be available in the cheaper plastics.
I did not allow any fitting gap between the motor and the new chassis parts. Because they have been printed to such a high level of accuracy the hole for the motor is the exact same size as the motor and consequently it won’t fit. This is easily remedied by grinding some of the inside of the chassis away. Alternatively I could have shaved down the motor casing. I ground the inside of the parts with a flat stone in an electric modeling drill. Simply grinding the surface flat and removing the layering effect was enough for the motor to fit.
The motor now fits and I have also updated the 3D model to make the fit a bit easier.
As well as extending the chassis both drive shafts needed to be extended by 5mm as the ends will no longer reach the gears on the motor. To do this I designed a 3D printed gear extender that will fit into the existing drive shaft gear as you can see in the rendering below.
The new part has been designed to be printed in Shapeways Frosted Detail plastics. This is the best material to ensure the accuracy of the gear teeth. My set was printed in Frosted Extreme Detail and below you can see how they came out.
Test fitting them into the original gears was a perfect push fit. Below you can see one fitted into a drive shaft. When it is time to fully assembly the locomotive I will put a small dab of super glue between the parts just to ensure they stay together although friction will do the job.
The next task is to finish the 3D model for the main body shell and set-out all the brass Additions. My other locomotive kits have brass Additions for handrails and parts as well as 3D printed handrails but for this locomotive the only handrails will be brass. I decided to do this because there will be lots of finally detailed handrail parts and if they are printed in plastic they are still a bit oversized and are very fragile. With brass etching I can get decently sized handrails as well as lots of other details such as grab irons and roof top walkways. Once I get the drawings done I will be sharing them with you.