Quick & Dirty Worm Wheel making

I was trying to make a substantial speed reduction to a small, but very powerful 230 Watt motor to drive a small auger.

PB131857s.jpg

The motor specs are impressive

Mabuchi Motor 12v Rs-775sf 230w 19500 rpm

Model : RS-775 18V Weight : 11.9 oz
Operating v : 6v - 20v Length of motor : 2.81 in
Nominal v : 18v Diameter (with flux ring) : 1.85 in
No Load RPM : 19500 Diameter (no flux ring) / Width Across Flat : 1.66 in
No Load A : 2.7A Shaft Diameter : 0.197 in
Stall Torque : 166.65 oz-in Shaft Length : 0.3 in
Stall Current : 130A Mounting Screws (2) : M4
Kt : oz-in/A
Kv : rpm/V
Efficiency : 78%
RPM - Peak Eff : 17040
Torque - Peak Eff : 21.00 oz-in/A
Current - Peak Eff : 18.7A

Currently, in a similar application, I use for this purpose the old plastic gearbox from “Gaucho Grande” jeep my kids had more than a decade ago.

PB131862s.jpg

It gives a reduction 134:1 so each motor drive the wheel at 144 rpms providing ample power!

Gaucho_gears1aa.jpg

My first thought was to make a proper gearbox to provide a 133.6:1 reduction using 4 sets of 68/20 teeth gears.

Gears.jpg

Then, considering the amount of work and complexity involved, I thought I could experiment with a metal worm gear that could provide the same reduction rate.
For the worm, I have some 12mm (1.75 pitch) steel threaded rod that fits the bill and a 70mm cylindrical bronze bar that I could use to make the worm wheel.

Using my band saw I have cut a 20 mm piece

P1271975s.jpg

Cleaned it on the lathe

P1281977s.jpg

Then I Center drilled it, removed the tool-holder and supported it on the topslide in a way that could rotate freely on the tool-holder bolt.

P1281982s.jpg

The center of the part is in alignment to the tool height of the lathe

P1281979s.jpg

For cutter I used a standard 12 x 1.75 tap clamped it on a drill chuck that in turn was centered it on the 4jaw chuck.

P1281978s.jpg

Next I started the lathe and the tap started cutting and rotating the part.

P1281981s.jpg

The teeth formed gradually while I was very slowly feeding in the wheel (towards the tap)

P1281983s.jpg

After an hour the worm wheel teeth were ready.

P1281987s.jpg

The tap had done a nice job. Now I must put the parts together and make the gearbox.

Thanks for reading

Petros
 
Last edited:
Back
Top