Lego trains - buffers, magcoupler, wheels

When you have enough bricks around to build lego trains attachment car, but no spare couplers, buffers and wheels - and all stores are actualy closed due to holiday season :-)…

Print settings

Modelled according to actual lego pieces and sliced to be printed without supports. Prototype was printed with 0.1mm layer height, 2 perimeters, 15% infill and 0.4mm nozzle in PLA and glued together using CA glue. The parts are designed for 0.4mm extrusion width on perimeters for best fit, but feel free to adjust to any values which will work for you.

Press a regular lego brick few times on the studs, they're designed with +0.2mm in diameter to account with shrinkage of filament during printing. A light touch up with file/sandpaper on the stud edges could help a bit during the first insertions. 

Other materials needed

Beside printed parts you'll also need 2mm steel rod for wheel axis and coupler attachment (40mm for wheel axis, 13mm for coupler attachment rod) and neodymium magnet dia 6mm  x 4mm to include in the coupler before gluing halves together. I used four 1mm magnets from my maker case.

Buffers and coupler assembly

The buffers are included in both versions: as single piece to print with supports, or version with plates separated to be printed without supports and glued together. For both versions, you'l need to glue the coupler cover on top of buffer support. Use 2x2 brick with four layers of plain office paper as spacer from back of the buffers - the coupler rod should be aligned with bottom hole. 

Before bonding the coupler piece together, please make sure the chamber for magnets is clear and the magnets could rotate freely agains curved back without getting stuck in corners or filament drops. A rotary tool with reasonable sized stone will be your friend. After inserting magnets, snap the parts together without gluing and check if you'll be able to snap some other magnet from both sides (both poles) to front of the coupler. The magnet inside the chamber should rotate freely allowing to attach any magnet polarity and thus any other car together without differentiating between front and back.

Wheels assembly

The wheel axis hole will be probably a bit smaller than 2mm after printing, use a drill suitable to you axis siameter to extend the hole in way that it firmly grabs the axis but the wheel itself don't wobble much around the axis. You can use few 2x2 block as simple alignment tool - see the photo. The same dril should be used for reshaping the back of wheel mask point of contact with the wheel. This is according the original lego design. Or you can file down the cone on wheel top and glue the wheels to their axis. That way it would skid in the curves of the track, but without much impact to smoothness of the run.

The wheel holder piece is divided into three subpieces. First file the mask holder ends on central piece to have flat surface for later mask glue up. The holder is designed approx 0.2mm wider on each side, so you can firmly touch the ends. Then glue wheel mask on one side.

Insert the axis rod, with both wheels and check with second mask if the wheels rotates fine. Adjust the depth of axis hole in wheels or the back bore of wheel mask accordingly. Then glue the second mask and you're done.

License

CC, free for non-commercial use. Remixes allowed with attribution of original source. 

For anyone interrested, the FreeCAD sources are also enclosed in the archive, anyone can modify them to suit their needs. I'm a self taught maker so please don't be angry if you'll find the design a bit akward / suboptimal. If you have any tips for improvements, feel free to contact me.

Have fun.