The problem with kit bashing is the spare parts left lying around afterwards! With the new Bachmann DDA40X chassis being used for my 3D printed DD35 models, Bob, who does the painting and assembling, realized he was starting to get a lot of spare, brand new DDA40X shells lying around and he came up with a great idea.  Why not print a dummy chassis and trucks to use with the spare shells? They can be used as dummy locomotives or even mid train helpers.

The DD35 locomotive shell was designed to fit directly onto the DDA40X chassis, after it was shortened by 24mm, and the DD35 dummy locomotive uses exactly the same shell.  So the theory is to take the DD35 chassis and lengthen it by 24mm which should make it into a DDA40X dummy chassis. The main differences would be the fuel tank and the ends of the new chassis. The DD35 dummy chassis, pictured below, has the fuel tanks permanently attached as part of the print and the ends are shaped to match the DD35 shell.

The DDA40X fuel tank was much longer then the DD35’s and was all one piece as opposed to being made from a pair of GP35 tanks.  Bachmann made the DDA40X fuel tank out of a strong plastic with a metal insert which added weight to the locomotive.  It was a removable item which clipped onto the underside of the metal chassis.  After lengthening the new chassis I roughly modeled in the DD40AX fuel tank and positioned it as shown below.

I added lugs which would drop down and line up with the fixing holes in the fuel tank, so when printed the real tank will clip on in the same way as it did to the metal Bachmann chassis.  The cross bar in the middle is designed to give some rigidity to the large opening but I made sure it was above the metal insert.  The ends of the chassis didn’t need to be as long as I originally intended because, as pictured below, the Bachmann shell changes shape at the ends, and the flat surface which sits on the chassis is interrupted by the lugs circled in red.  This also repeats at the other end even though there is no cab.

I decided to stop the new chassis at the lugs and, because the couplings are a part of the truck assembly, any more material used past the lugs would be redundant and only add to the cost.

As there is no detail on this chassis, because the original fuel tank is being reused, it didn’t make sense to print this in the FUD material as it would be more expensive, therefore this chassis will be made from Shapeways’ White Strong & Flexible (WS&F) material.  This is my first print using this material and it has some different design criteria; mainly that the minimum thickness of material is higher. However, even with thicker walls, the cost works out a lot cheaper than if printed in FUD.

The final design for the new chassis looks like this.

The test print will be printed in the WS&F material along with some DD35 dummy trucks in the FUD material.  Although these trucks technically are not correct for this locomotive it will be a good test to check the chassis.  The plan is to draw up some DDA40X trucks to be made available with this chassis by revising the DD35 truck design.

Next time I will show you how the WS&F material came out and the process of finishing the model.