Parts.

I acquired the following parts:

• One 100RPM 6VDC gear motor.
• One miniature slide switch.
• One 3.7VDC 100MA lipo battery with suitable charger.
• Two 1" diameter slinky toys.
• Forty eight 3mm diameter by 1mm thick neodymium magnets.

I 3D printed the following parts at .15mm layer height, 20% infill, no supports, .4mm nozzle in PLA unless noted otherwise:

• One "Cap.stl".
• One "Motor Mount and Traveler Pin Guide.stl".
• One "Screw.stl" at .1mm layer height, 20% infill, .25mm diameter nozzle, Tough PLA.
• Two "Slinky Pad.stl" at .15mm layer height, 20% infill, .4mm diameter nozzle, Tough PLA.
• One "Stand.stl".
• One "Traveler Pin Guide.stl".
• Two "Traveler.stl" at .1mm layer height, 20% infill, .25mm nozzle, Tough PLA, with supports.

This is a high precision 3D print and assembly model using at times very small precision 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.

Assembling the Self Reversing Screw Mechanism

To assemble the self reversing screw mechanism, I performed the following steps:

• Temporarily adhered one "Traveler.stl" to "Motor Mount and Traveler Pin Guide.stl" using petroleum jelly as shown.
• Positioned "Screw.stl" into the assembly, sliding the axle into the round hole in the top of the assembly, and making certain the traveler was properly positioned in the screw upper turn around.
• Slid the motor into the assembly with the motor shaft fully inserted into the screw.
• Temporarily adhered the remaining "Traveler.stl" to the screw lower turn around using petroleum jelly.
• Pressed "Traveler Pin Guide.stl" onto the assembly.
• Pressed "Cap.stl" onto the top of the assembly.
• Pressed 24 neodymium magnets into each of the two "Slinky • Pad.stl" four magnet pockets, three per pocket, making certain all polarities matched.
• Snapped one of the slinky pad assemblies onto the track over one of the traveler pin.
• Snapped the remaining slinky pad assembly onto the opposite track over the remaining traveler pin.

Assemble the Stand.

To assemble the stand, I performed the following steps:

• Glued the slide switch to "Stand.stl".
• Attached the battery to the stand assembly using double sided tape then:
• Trimmed the female JST connector wires to 60mm, then stripped and tinned the ends.
• Soldered a 40mm length of black wire to the slide switch outer terminal.
• Soldered the female JST connector black wire to the slide switch center terminal.
• Pressed the self reversing screw mechanism into the stand assembly, then:
• Soldered the female JST red wire to the gear motor "+" terminal.
• Soldered the 40mm length of black wire on the slide switch outer terminal to the motor "-" terminal.
• With soldering complete, I made certain the slide switch was off, then attached the battery male connector to the JST female connector.
• Carefully tucked the excess wire into the stand.
• Glued the self reversing screw assembly to the stand assembly.

Final Assembly.

For final assembly, I simply attached each slinky to the model as shown, turned on the power switch, and off it went!

And that is how I 3D printed and assembled, "Self Reversing Screw Mechanism, Slinky!".

I hope you enjoyed it!