Drawing a Dummy Chassis & Trucks for an N Scale EMD SD50

As promised in last week’s post this week I have another design for a 3D printed product to share with you. This one has been knocking around my drawing board, or laptop, since last year so it’s time I got it finished.

So far I have tried to supply a dummy chassis and trucks for the spare locomotive shells left over from donor locos.  For example, I have made a dummy chassis kit available for the Bachmann DDA40X and the Atlas C-628/630.  These locos are donors for my EMD DD35, Baldwin DT6-6-2000 & Baldwin RT-624.  A dummy kit for the Con-Cor U50/Turbine is on its way.

I have also been asked to supply dummy locomotive chassis kits for other shells.  I have several on their way but the first is for an Atlas’ SD50, in particular this Norfolk Southern one.


Drawing the actual chassis part is fairly simple, as it will mostly be hidden, so there is very little detail to worry about and I can stretch the one used for the Atlas C-628/630.  The biggest challenge, apart from getting the size right, is to reduce the amount of material used so it’s cheap to print but still strong.  The actual chassis, shown below, is designed to clip into the shell using the same mounting points found on the metal power chassis.  These are on the four upstands. My first design for this system had a solid bar across the top of the upstands,, however this made them too inflexible and it was very hard to get the shell off the chassis.


Also any parts that normally protrude into the original chassis have to be accounted for with notches and cut outs.  These are often used as locating lugs designed to get the shell in exactly the right place, which also helps me.

The fuel tank on these Atlas models is a separate injection molded part so the chassis has been designed to receive the tank using the same fixings. Luckily this is simply a longer version of the fixing for the C-628/630 fuel tank so again I can stretch my existing design.

The trucks are the more difficult part because these are on show and there’s normally a lot of detail here.  EMD built their SD50s with two different types of trucks.  The HT-C trucks, which can be identified by the hydraulic shock on the side of the middle axle of each truck, or the earlier Flexicoil trucks.  Only Conrail opted for the Flexicoil trucks so as this model is a Norfolk Southern I have modeled the HT-C style.  Once all the complicated visual parts were complete I had to design a new center section which missed the wheels and held the bolster pin in the right place. The bolster pin is shown below but will be a separate part.


As with my previous trucks I have spaced the truck frames to receive 3 Fox Vally 36″ metal wheel sets (FVM3611).  And I have made the same provision for electrical pick-up if required.


The axle wipers only make contact with the two outer wheel sets but this is enough to power the original circuit board or a pair of LEDs.  Below is a photo of an actual C-628 dummy truck fitted with the power pickups.  Each truck only picks up power from one rail.


To use the original lighting board the same clips I used for the C-628/630 can be used as you can below.

Alco C-628 Dummy Chassis Render 12

This fastens around the circuit board and clip into the top of the chassis over the fuel tank void.


I have a few more checks to make and then these parts will be ordered for a test print.  When they arrive I will share the results with you before making then available through my shop.