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Quick & Dirty Worm Wheel making

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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

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Cleaned it on the lathe

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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.

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

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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.

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

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

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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
 
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Comments

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

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

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I prepared the threaded rod
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Tested bearing fitting

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Worm ready!!

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Prepared bearing supports

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Created all openings needed

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Placed all components inside and bolted together



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Worm and worm gear are meshing nicely.

P2052011s.jpg

Gearbox works as designed to do!!

P2052015s.jpg

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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