Last Friday I had a delivery from Shapeways containing the new truck centers and gears for the HO Baldwin DT6-6-2000 project. They look good, and although there were a few issues, I thought I would share with you how they came out and what was wrong, rather than order some more and just show you the finished item.
I usually order several parts for different projects at the same time, with some of them combined on a sprew. Below you can see the truck center frames and lots of parts including the four new gears; they are located to the left of the sprew.
The four new gears are small and I didn’t want any parts of the sprew to touch them as it would need to be cut off, leaving a rough surface. So I surrounded them in a cage, which worked well.
The gears were free to move about, but couldn’t fall out.
Close up, the new gear is a good match for the original; the new gear is still covered in 3D print residue, which is why it looks a bit fuzzy.
The truck centers came out very well and appeared to be a direct replica of the original, with the desired changes.
The first problem came when I started fitting the gears into the holes. Each gear has a shoulder and an axel on each side. The axel fits into the hole and the shoulder acts as a spacer to position the gear in the center of the frame.
But in the 3D model, I’d forgotten to make the shoulder part of the gear, so it was 3D printed as a separate part which just happened to be close enough that the support material held it in place.
The axel and shoulder simply come off and you can see all the support material in the middle of the gear. The same thing happens on both sides so you end up with a flat gear with a hole in it.
Thankfully, this is why we print test pieces, and I was able to quickly fix the 3D model, so next time I print these gears they’ll be one whole piece. Sadly, for now, it means I can’t test all the new gears in the truck center. Interestingly though, once I had cleaned up all of the 3D print residue, the shoulder fitted into the hole in the gear so precisely I did wonder if I could make it work, but that made the axels too short and they wouldn’t stay in the right place. It does go to show how precise the 3D printer is.
The next test was the driveshaft and worm gear. These have brass bearings either side of the worm gear which clip or slot into the top of the truck center, and it fitted well allowing for good free movement, but without clamping the worm gear.
As you can see below I did try and fit it all together with the gears, and they did turn before they fell out. The big problem here is with the tubes which stick out from either side of the truck centers. The ones on the left are longer than the ones on the right. These tubes are the fixing locations for the truck side frames which hold the wheels and power pickups in place. One is longer than the other, because the shorter of the two also clamps the power pickups in place.
But as you can see below, I got these round the wrong way. The power pickup is clamped by the longer of the two tubes causing the truck side frames to flare out. And this made it impossible to properly test the trucks.
This error has also been fixed in the 3D model and a new set has now been ordered. To be fair, apart from the issue with the gears and the tubes, the truck centers came out very well, and with the corrections made, I feel we shall have a decent working truck with the asymmetric axels positioned the right way round. In the photo below you can see on the left truck, even though the side frames are flaring, the wheels are all in the right place.
These truck centers will work for both the Commonwealth and Tri-Mount Trucks, so they can be used for either the DT6-6-2000 or the RT-624 models. While the new truck centers and gears are being reprinted, I’ll finish off the 3D model of the shell, and I plan to share that with you next week.