Replica Railways/Bachmann OO Locomotive Split Axle Repair

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.