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.


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.


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


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


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


Cleaned it on the lathe


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.


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


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.


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


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


After an hour the worm wheel teeth were ready.


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

Thanks for reading

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I just hate the terms "quick and dirty" or "cheap and dirty". Maybe that's because I had a boss that used it a lot...

That's a nice job right there! Good thinking.
I just hate the terms "quick and dirty" or "cheap and dirty". Maybe that's because I had a boss that used it a lot...

That's a nice job right there! Good thinking.
I could use the right terminology if I knew it... BUT

QUICK describes the procedure properly, as for DIRTY it describes my lathe afterwards!
It works surprisingly well!

It took some steps before the final assembly though:

I prepared a sheet metal to form a box


I folded and welded the sheet metal (I do not have a sheet metal bender yet)


I prepared the threaded rod

Tested bearing fitting


Worm ready!!


Prepared bearing supports


Created all openings needed


Placed all components inside and bolted together


Worm and worm gear are meshing nicely.


Gearbox works as designed to do!!


I know, I know it needs cleaning, painting and all the rest of treatment to look nice but it is a job that could be done later...

On the other hand it is the definition of QUICK AND DIRTY GEARBOX
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