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Cross-axle holders for 2mm axles!

The 5mm variant of the cross-axle holders for 2mm axles applied to S-sized wheels.

These are adapters for standard Lego wheels to 2mm axles so you can mount them on proper bearings without using third party wheels. There are two versions of this. One of them is 8mm long while the other is 5mm. The 8mm variant has the length of a whole stud and is useful for all kinds of wheels besides the standard S-sized wheel, the 5mm variant is designed for. You can use the 8mm variant for S-sized wheels as well, but the axle will stick out of the wheel that way. While I'd consider this annoying most of the time, this could as well be a feature in case you want to hide the use of the 2mm axles on retrofitted designs.

The 5mm variant of the cross-axle holders for 2mm axles seen in CAD.

To apply them, I recocmmend adding them to the wheels first. The flange shall be on the inside of the axle. The fit on the 2mm axle will be quite strong to ensure it staying in place. Regardless, there still is a chance of the wheels slipping. Thus, I can not recommend using this for drivers coupled by rods.

How to print

Printbed with one cross-axle holder seen in bambu studio.

Print them with the flange on the printing bed.
I use a 0.2mm nozzle, but I could imagine this part being simple enough to work with a 0.4mm nozzle as well.
I recommend using a paper towel to remove the print from the printing bed to avoid grease on the bed.

Dimensions and download link

Drawing of the cross-axle holders.

I suspect my printer to be a bit on the overextruding side of things. Thus I show you the size of the file here. The inner fit should range around d=1,95 to d=2,00 on your prints. The outer fit should range around D= 1,8 to D=1,85 on your prints.
Tthis part does have demanding dimensions and should be adjusted in your slicer to work with your printer. It's important to both nail the inner fit for the axle to hold tight, as well as to have the cross hold your wheels properly. There might also appear a case where different kinds of wheels need different fits on the cross.
To adjust the fit, I can recommend working with over/under-extrusion as well as scaling the model slightly.
Download the .step file for the 5mm variant here.
Download the .step file for the 8mm variant here.

What kind of axle to use?

These fit well on 2 mm x 40 mm axles for standard L-gauge. These are the same axles Lego uses for their proper train wheelsets as well.
I've experienced some axle being a bit larger on the ends of the axle, this is fine and the assembly should work regardless.
For narrow gauge, they might fit with 2 mm x 25 mm axles. But I have not tested that. In case they do not, please inform me, I'll adjust the model for them to fit as well.