HO gauge locomotive repair parts: drive gear and coal car linkage

thingiverse

This set features an axle drive gear that mates with the motor shaft's brass worm gear and a coal car linkage to restore a broken HO gauge locomotive of unknown manufacturer. The goal was to return a defective engine we acquired, which came with a worn-out drive gear and broken linkage, to full functionality. I removed the 18-tooth gear as further research revealed that the original gear had only 16 teeth, explaining why replacement gears were wearing out so quickly. The linkage may require adjustments for length to position the coal car correctly relative to the engine or to ensure the connecting peg holes are the right diameter. The SCAD file source is available for editing to suit your needs. To create a usable gear from a rough 3D printed one, follow these steps: 1-Fill in the top surface of the gear wheel with enough acetone-ABS paste to coat that area. 2-After 30 minutes of airflow, press the mostly dry wheel against a flat steel surface to ensure the filler penetrates fully. 3-Twelve hours later, sand both sides and drill out the axle shaft opening for a snug fit. 4-Fit the dry ABS plastic printed gear wheel onto the axle shaft. Acetone may aid in this process and improve adhesion when dry. 5-Once the axle is inserted, hold the drive gear wheel/axle tight to the worm gear with your fingers, then have someone control the power while running it slowly for a few minutes. 6-Add some acetone to soften it, let it absorb, then run it for another 5 minutes and allow it to dry for a few hours. 7-After drying, run it dry for 5 minutes before greasing with lithium blue bicycle bearing grease and assembling the model engine. 8-Run the fully assembled model engine on the track for about an hour, half of that time in reverse, monitoring for binding and lubricant wear. The wheel's dimensions are as follows: 1cm diameter, 9mm without teeth, and 4mm wide teeth slanted at 5 degrees (interface with a slanted worm gear). At this scale, using a 5mm extruder, there was no need to bevel the gear teeth, as it would have left more plastic to grind during wear-in. The 2.4mm diameter hole in the center is tight enough to fit snugly onto the axle shaft but may require drilling or reaming out. V1.1 has enlarged the coal car peg and axle shaft holes by +1mm and +0.4mm, respectively, and made the linkage thicker and longer teeth on the drive gear (+0.5mm). I have yet to print and test this model, so please comment if it performs better. Since we were also wiring a caboose for lights powered from rectified DC rail voltage, I've uploaded that schematic as well.