Parts.

I acquired the following parts:

• One N20 100RPM gear motor.
• One twin AAA switched battery pack.
• Four 8mm ID, 16mm OD, 5mm thick flanged ball bearings.
• One 3mm diameter by 1mm thick neodymium magnet.
• One lever switch (CYT1073).
• One reed switch (EK1621, 14mm by 2mm tube).
• Two M2 by 20 cap screws and nuts.

I 3D printed the following parts at .1 mm layer height, 15% infill with no supports in PLA unless noted otherwise:

• Two “Axle Sprocket.stl”.
• One “Base.stl”.
• One “Belt Support.stl”.
• One “Belt.stl”, TPU.
• Eighteen “Bolt (M8 by 1.25 by 8).stl”.
• One “Bolt (M8 by 1.25 by 14).stl”.
• One “Cover.stl”.
• Seven “Domino Mount Axle.stl”.
• Seven “Domino Mount.stl”.
• Seven “Domino.stl”.
• One “Front.stl”.
• One “Motor Mount.stl”.
• One “Rear.stl”.
• One “Reed Switch Mount.stl”.
• Two “Sprocket Cap.stl”.
• Two “Sprocket.stl”.
• One “Top.stl”.

This is a high precision large format 3D print and assembly model using at times very small precision 3D printed parts in very tight spaces. Prior to assembly, test fit and trim, file, sand, polish, etc. all parts as necessary for smooth movement of moving surfaces, and tight fit for non moving surfaces. Depending on you printer, your printer settings and the colors you chose, more or less trimming, filing, sanding and/or polishing may be required. Carefully file all edges that contacted the build plate to make absolutely certain that all build plate "ooze" is removed and that all edges are smooth. I used small jewelers files and plenty of patience to perform this step.

The model also uses threaded assembly thus an M8 by 1.25 tap and die will assist with thread cleaning if necessary.

Assemble the Belt Track.

To assemble the belt track, I performed the following steps:

• Pressed one flange bearing into each end of "Front.stl" and "Rear.stl" as shown.
• Pressed one "Axle Sprocket.stl" into one of the flange bearings in the rear assembly as shown.
• Pressed one "Sprocket.stl" onto the axle sprocket.
• Pressed one "Sprocket Cap.stl" onto the axle sprocket.
• Repeated the previous three steps for the remaining end of the rear assembly.
• Attached "Belt Support.stl" to the rear assembly using three "Bolt (M8 by 1.25 by 8).stl".
• Attached the rear assembly to the front assembly using three "Bolt (M8 by 1.25 by 8).stl".
• Positioned "Belt.stl" over both sprockets.

Assemble the Top.

To assemble the top, I performed the following steps:

• Positioned one "Domino Mount.stl" into "Top.stl" and secured in place with one "Domino Mount Axle.stl" making certain the domino mount rotated with ease.
• Glued one "Domino.stl" to the domino mount mounting pin making certain the domino stood perpendicular to the top surface and carefully noting the orientation of the domino on the pin as shown in the wireframe view.
• Repeated the previous two steps for the remaining domino mount, domino axles and dominoes.
• Glued one 3mm by 1mm diameter neodymium magnet to the last domino mount lever arm.
• Secured the top assembly to the belt track assembly using four "Bolt (M8 by 1.25 by 8).stl".
• Attached "Base.stl" to the assembly using six "Bolt (M8 by 1.25 by 8).stl".

Final Assembly.

For final assembly, I performed the following steps:

• Carefully inserted the reed switch into "Read Switch Mount.stl" with the reed switch tube flush with the mount, soldered an 80mm length of wire to each reed switch terminal, then glued the wires to the read switch mount for strain relief.
• After removing two of the 8mm bolts from the rear of the assembly, I attached "Motor Mount.stl" and the read switch assembly to the belt track assembly using one "Bolt (M8 by 1.25 by 14).stl", positioning the reed switch mount as shown.
• Pressed the gear motor into the motor mount assembly and into the axle sprocket.
• Attached the lever switch to the base using the two M2 by 20 cap screws and nuts.
• Using the schematic, I wired the motor, battery pack, reed switch and lever switch as shown.
• Inserted two AAA batteries into the battery pack and turned the battery pack switch off.
• Attached the battery back to the belt track assembly using double sided tape.

At this point, I turned on the battery back and made adjustments to both the reed switch position (such that the motor would start when the last domino fell) and the lever switch position (such that the motor would stop when a belt tab pressed the switch lever).

With adjustments complete and the mechanism operating properly, I slid "Cover.stl" over the assembly and attached with four "Bolt (M8 by 1.25 by 14).stl".

And that is how I 3D printed and assembled "A 'Do Nothing' Dominoes Box".

I hope you enjoyed it!