This week I’ve some more progress to share with you on my HO scale DT6-6-2000 project.  I’ve been making lots of small changes, many internally which are hard to see, but also several to the exterior.

The body shell model, as shown below, now has all of its brass handrails positioned, along with their corresponding locating holes.  Unlike the N Scale version, I will only be producing brass handrails for this locomotive because a 3D printed set, at the correct scale thickness, will simply be too weak and they’ll break very easily.  The brass will be strong and when fixed into the mounting holes should stand up to the little knocks and bumps all of our trains accidentally get.

Last week I left you with my idea of adding the Preci Models DCC auto uncouplers directly to the locomotive.  To make that work, I needed to figure out the connection between the chassis and the body shell, then how to mount the Preci motor.

Because DT6-6-2000 is longer than the donor C-630 chassis the coupling is moved forward, allowing the original coupling mount hole to be used only as a body shell fixing.  As you can see below, with half the body shell hidden, I’ve created a hole in the body shell above the chassis hole along with a cutout for an M3 nut.  The nut will drop into the cutout becoming captured and can be glued in place.

Then an M3 bolt can be used to secure the body shell to the chassis.  Because the chassis tab with the hole fits into a recess in the body shell, both will be in the right place.

With the body shell secured, and without the need to modify the chassis, I can now look at the couplers and the Preci motor.  The Preci motor can be mounted in many ways but normally it’s glued to the back of the Kedee coupling as shown below. (Pictures from http://www.precimodels.com).  This allows the actuating string to run parallel to the coupling to give a straight pull.

With anything like this, my first step is always to model in the parts, so here is the Preci motor.

Using the model I can then accurately position the motor, and, as you can see below, there’s not enough room between the coupling and the chassis to mount it.  I also find mounting the motor like this can be rather fiddly as you need to glue it in just the right place.

My solution is to mount the motor vertically in a 3D printed hole.  This has the advantage of correctly locating the motor horizontally and vertically.  The large hole doesn’t go all the way through, creating a pocket for the motor to sit in.

The motor would be fitted before the body shell is bolted on top of the chassis.

The space between the coupling and chassis is still tight, but as the rotating part of the motor is so small and will only have a thin string attached to it, there should be room.  Connecting the string should also be done before the chassis bolt is fitted for ease of access.

With a bit of luck, and mostly modeling time, I’m hoping to have the body shell modifications done by next week.  I also intend to make the horns separate parts to allow different horns to be fitted, which was a recommendation from a fellow modeler.  Currently, as shown below, the horns are 3D printed directly onto the shell.

I’ll also be adding brass windscreen wipers, a cab interior and routing for wires to give cab lights.  The N scale version had provision to add working headlights, but due to the size constraints, the marking/number board lights on the noses were not illuminated.  But I’m considering this for the HO version.  They will still be small but it’s not impossible.  I’ill share my progress with you next week.