Two weeks ago I shared with you the first 3D test print for my new HO scale DT6-6-2000, you can find the post here.  As you may recall I had a few issues with the print, but this week the second test print arrived and the results are very good.

I reprinted the two truck center halves and the four gears as all had issues to be resolved.  The final kit will need four truck center halves and eight gears.

The gears came out even crisper this time, I assume because the axel section of the gear is now a part of the gear rather than held in place by 3D print residue.

The gears up close are very accurate, but there’s still some residue on the axel which will need cleaning off. To do this I simply wipe it off with paper towel. The holes for all the gears will also need cleaning out and for this I use a drill to ream each hole.  If it has 3D print residue in the hole it will cause the gear to bind and add drag to the motor.  If all the holes bind it may even jamb up the gears.

This time everything fitted as planned.  The clip covering the worm gear will need to be taken off, and the drive shaft removed, in order to fit it into the chassis.

The gears, as shown below, are simply positioned in place to check they are a good fit.  Before I tested them under power from the motor I did all the cleaning mentioned above, and lubricated all the axel holes with light oil, from inside and out.  Then, with the wheelsets removed, I checked that the sets of gears turned freely by running my finger along them.  With the wheelsets refitted the whole assembly was a little tougher to turn, but this was expected given there are 3 more gears than in the original configuration.  But once the driveshaft and worm gear was fitted I was able to turn the whole assembly by hand.

The test fit into the chassis was also good; below you can see the original truck on the left and the new one on the right now facing the right way for a DT6-6-2000 or RT-624.

The clip covering the worm gear holds the truck in place, and a pin in the underside of the chassis fits into a hole at the center of the truck, creating the pivot point.

The white of the truck center is barely visible through the truck side frames, but it can be painted, taking caution not to paint the axel holes.  With the chassis reassembled, albeit with one new and one old truck, I lubricated the gears using oil designed for plastic gears from LaBelle. You can find a post about these products here.

The final thing to do was test the new truck, so I connected a basic DC controller to the chassis (there is no DCC chip fitted yet) to see how well it runs.

In the video below you can see I ran the chassis at full throttle in one direction then threw it into the other.  Because of the two large flywheels, the direction change is not instant, but it’s still a heavy load on all the gears and they seem unaffected.  The chassis is in a foam holder because the first time I did this the sudden reverse toppled the chassis over!

The new truck ran very smoothly and the slow speed looks okay, but the real test will be when it’s on some tracks.  As I’m an N scale modeler I only have a short section of HO track at home, but later this week I’ll be able to test it on a layout.  The chassis has an 8 pin DCC socket so I can plug in a chip and see how slow I can make it crawl, but I feel confident that I’ve resolved the issue with rotating the trucks, so now it’s just a matter of finishing the shell.  I’m currently modeling the cab interior and I will share that with you when it’s finished and before we go to test print.

In January of 2019, I shared with you my design for a 3D printed axle set to fix Mainline steam locomotives with the large drive gear on the center axle.  You can find the post here.

The manufacturer Mainline was incorporated into the Bachmann company and several of the designs stayed the same.  These are what I call the large center gear models, and have the square shafts on the wheels, such as this modified Hall locomotive below.

But another popular brand which Bachmann also incorporated was Replica Railways.  These locomotives, such as the LNER B1 below, have a similar design to the Mainline locomotives in that they are a split chassis design without wires, but the main difference is the motor and the power transmission to the wheels.

These have a totally different motor that drives the rear axle via a smaller gear than the Mainline locos.  The side rods then drive the forward wheelsets which have ungeared axles.

Along with the rear gear being smaller, so are the axles, and sadly the wheels do not have square shafts.  This causes the wheels to get out of quarter when the axles split and everything jams up.  These are also made from the same material as the Mainline ones and it’s very common for them to crack and split.

This particular model had at some point been repaired in the past and the standard method for this was to glue the damaged axle in place. This means when the axle finally breaks down completely there is glue in the wheel which prevents a new axle being fitted.  In the photo below you can see the pocket around the center stub is full of glue.

To get this out I drill several holes in the glue until it starts to break up and can be pulled out with tweezers.  This also depends on the type of glue that was used.

Below you can see the holes I started drilling in the glue.  Make sure you don’t go too deep and start drilling into the wheel. The way to check is to look at the swarf coming out.  This particular glue was fairly transparent so as soon as a fleck of silver came out I knew I was as the bottom of the pocket.

Once all the glue is removed you should have something which looks like this.  The rear axle, which has the geared axle, usually has traction tires.  The center wheels have a larger connection for the side rods as this is also where the piston rod and eccentric rod attach.

The three axles have been drawn up and printed in my usual material, Shapeways Smooth Fine Detail Plastic.  I’ve put them on a sprew, which doesn’t actually touch the parts, for ease of printing.

Because these axles have round holes it means unless the wheel is a good fit it can easily rotate inside the axle, but if it’s too tight the wheel will split the new axle, just like the original.  Because the Mainline axles have square holes this is less of an issue.  I’ve purposely drawn the hole in the axles ever so slightly smaller than the wheel center stub.  I use a drill to carefully ream out the hole because, as I have shown in other posts, there will always be 3D print residue in the hole and it needs to be a perfect fit.

The axle can then be pressed onto the wheel; it needs to go all the way into the pocket.

The corresponding wheel can also be fitted but at this stage, it’s vital to get the quartering right.  This means one wheel needs to be rotated 45° to the other.  Each wheelset must be set in the same configuration.

All three wheelsets can then be replaced in the chassis.

Often at this point is I get asked which way round all the rods connect, so I’ll run through the sequence.  Below you can see the simple side rod connects the center wheel to the front wheel.  The joining side rod, shaped to represent a side rod joint, connects the rear wheel to the center.

The joining side rod is connected first, hooking over the connecting peg.

Second is the simple side rod sitting on top of the joining side rod.

Third is the spacer, with the grooved side facing up.

Fourth is the piston rod, which fits over the spacer.

And lastly, the eccentric rod fixes into the wheel with the special screw which holds it all together.

Testing the loco is always, hopefully, a happy moment and I like to test motion before the loco is put on the track.  Below is a video of the first test.  The slow speed is a little lumpy partly due to the motor but this went away once it had done a few laps of a test track.

Because the hole in the axles needs to be such a good fit and I’ve come across some variations in the size of the wheel pegs, I’ve provided a spare axle with the set so you can use this to check and see if it fits or whether it needs enlarging.

The axle and gear set can be found here.

Despite being harder to install than the Mainline kit, mainly due to the quartering issue, these do work well as a repair and I’ve fixed many damaged Replica Railways locomotives which, without the part, would be redundant.

I have some more 3D printed gears in my latest test print and once I’ve installed and tested those I’ll share them with you as well.

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.