3d Printed Hand Crank Compound Gear Train

This project was meant to test my CAD and 3d printing capabilities and involves a stand, five double helical compound gears and the final driven gear, and a handle.

Every 3d print was designed by me.

This is a very simple design of a gear box and can be used to change speeds with the tradeoff of less torque.

The gear ratio gets multiplied by three every gear, and with six compound gears this totals to 3^6 or a ratio of 243 for the final gear.

I decided to use bearings due to the high speed to keep the friction low and the movement smooth.

5 double helical compound gears, 1 driver gear, 5 spacers 1 stand, 1 handle, 2 pins.

150g~ of 3d printer filament

10 Bearing: 6x19x6mm

2 aluminium axles: 6x6x100mm

I debated between five to six total gears but chose six to be on the safe side and found the resistance

Double helical gears fit my situation best, due to the locking of the teeth and reduced noise and vibrations.

I was debating between a 4.5mm or 6mm axle but after I preformed a stress tests found I the 6mm axle to be a safer choice.

I decided it was necessary use shaft pin connections for easy rotation of the gears, as glue wasn't sufficient.

After deciding on 6mm for the axle, I had to use bearings also with a 6mm bore to keep a good fit, I ended up using two bearings per gear with a spacer in the middle.

I went through mainly four different gear designs changing things like clearance, thickness, and clearance between the spacer and axle.

The first things to be printed were the compound gears and the spacers because they work together to make a space in between the bearings, the main reason I didn't print these as one file was because of the overhang, I tested printing without supports and it had problems with stringing, and with supports it was too difficult to take them all off without touching the ball bearings.

Next I printed the stand, with a spacing of 71.05mm the gear teeth have a clearance of around 0.15mm~, its hard to get the exact number due to the filament bulging outwards though.

The first handle I made broke when I pushed it to its limits so my newer handle had more support and so far has worked without breaking.

The printing phase saw changes and modifications but for the most part my mechanical solutions worked well enough.

Out of every stage this was by far the hardest and most time consuming one, also everything was printed on flashforage adventurer 4 or 5 pro printers.

I used two bearings and one spacer in an oreo like configuration, I also used friction fitting and epoxy to prevent slipping. Then repeated this for five more gears and printed the stand.

After drilling 2 holes into one axle around 15mm~ apart I put two compund gears and the driver gear on the axle, and three compound gears on the untouched axle.

Lastly I added the handle and put the two pins in little slots in the 3d print and axle to make a shaft pin connection to lock everything in place.

The hindsight from what I know now would've really helped, if I could remake this or if anyone wants to attempt this I would recommend 0.10m~ less clearance between the teeth, stronger fit with the axles and stand, a better type of bearing and the use of a lubricant to help efficiency.

It also took me a very long time to drill the holes into the axles and they ended up being off center and didn't look very professional, filing the curved surface before would've also made it easier to drill the holes.