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G-Scale model railway coupling adapter - LGB to Kadee Knuckle coupler - 3D design and print

Replace LGB 0-4-0 Small Steam hook loop and pin, with kadee type E using FreeCAD

Since starting a G-Scale outdoor railway I've learned lots about the hobby. One of the things I've learned recently is the complicated world of knuckle coupler options.

Up to this point we have mainly LGB trains and compatible rolling stock. All of which used hook loop and pin couplings. My son has received a new American 0-6-0 Baldwin locomotive for Christmas. It's a Bachmann locomotive which came with Bachmann knuckle couplers. We were going to look at rolloing out knuckle couplers on some more of our rolling stock, however since buying that we also bought some wagons which came with Kadee knuckle couplers. Unfortunately the two don't work together.

G-Scale Bachmann locomotive with chocolate laden wagons

Although Bachmann couplers are cheaper and if we replaced lots of couplers may save money, we decided that the fact that we now had some wagons with Kadee couplers then it would be cheaper to replace the one Bachmann coupler than replace the other 2 pairs. It also happened that the shop we were in at the time had Kadee in stock, but no Bachmann couplers. They even had two different types of Kadee couplers some older ones in the bargain bins and some brand new. We didn't know the difference at the time, but bought both pairs of the older ones and two packs of the newer ones, which has worked out even better.

After getting them home we later released that one of the older couplers known as type E could be used to replace the coupler on the Bachmann loco, but neither of the ones we had could be used on our existing LGB trains. There is a Kadee large scale coupler conversions guide although we didn't have the type required, and the shop we'd been to didn't stock them anyway. The particular coupler we required is known as an Original Large Offset Coupler.

So plan B, design my own adapter which could be used to connect between the LGB locomotive and one of the Kadee coupler types I had. I decided to go for the Kadee type E as it is shorter (so would not extend the gap between the loco and the wagons so much) and was easier to connect to. So I designed my own adapter using FreeCAD.

FreeCAD is perhaps not as easy to learn as some alternative CAD packages, but it is incredibly powerful and actually makes designing accurate parts quite easy. See the following for a getting started guide for FreeCAD.

The FreeCAD design is shown below. The wider part goes inside of the LGB locomotive and the narrower part fits into the Kadee coupler". This was designed by using digital calipers to measure the existing parts from both LGB and Kadee.

Adapter for LGB to Kadee coupler designed in FreeCAD

This was then 3D printed, the existing coupling removed and this was inserted into the loco and screwed to the Kadee type E coupler. I had intentionally made the hole for the loco end a little small (when used with self-tapping screws it's better to make a hole too small than too big) and I had to enlarge is slightly with a drill. I also sanded the part down a little which gave a snug fit.

LGB loco to Kadee type E knuckle coupling adapter

The image below shows this in use.

LGB train with Kadee knuckle coupler - 3D printed adapter

More about the model railway and related projects

The video below provides an introduction to my garden model railway. This is one of my earlier YouTube videos on my channel. There have been a lot of changes to the railway since and many related projects.

Download Files

The files can be downloaded from my Thingiverse collection.


Although it would have been possible to buy alternative brackets this was designed and printed in less than an hour. It avoided needing to find a supplier with the appropriate part in stock and the wait for it to be delivered. It was also considerably cheaper costing less than £1 compared to around £16 for a new adapter (I already had a spare type-E). This is based on the fact that I already had a 3D printer.

A disadvantage is that this comes further out of the locomotive compared to getting the correct Kadee adapter.

I think it's a good example of what can be done if you have a 3D printer.

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