# Worm gear for a homemade rotary table



## Meleon69 (Oct 24, 2019)

New photo by Jamie MacInnis
					






					photos.app.goo.gl
				






I robbed this worm gear set from a the gear box of an old walk behind snow blower. I’m hoping to use it for a rotary table build. I couple of questions.
1. How do I determine the gear ratio?
2. Will it be too be to be practical?
I can provide more measurements. Just tell me what measurements are needed


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## RJSakowski (Oct 24, 2019)

One revolution of the worm advances the gear one tooth.  21 teeth so 21:1.  That would be an odd number for an RT. Also an RT usually has a mechanism for taking up any slack to reduce backlash.  This would be hard to accomplish with your gear set.  However, if you are willing to do the math and only turn the table in one direction for its final setting, it could work.


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## RJSakowski (Oct 24, 2019)

Each revolution of the worm would rotate the table 17.1429º or 17º 8' 34.29".


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## Meleon69 (Oct 24, 2019)

Thanks for the reply. I knew there must have a reason I couldn’t anybody using them for any but there intended purpose. They are pretty robust and seem well made.


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## MontanaLon (Oct 24, 2019)

Following. A rotary table would be nice, being made of junk is not a negative in my book.


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## Meleon69 (Oct 24, 2019)

MontanaLon. This won’t break any speed records. My mill is currently in another province. Hope to fix that on the week. Stack that with the fact that I work a fly in fly out job. I’m home 1 week out of 3. But I’ll happily keep the group up to date with progress.


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## MontanaLon (Oct 24, 2019)

I am in for the long haul. Still have to find a snow blower I can scavenge from.


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## Meleon69 (Oct 24, 2019)

The older ones from the 80’s have lots of shafts, bearings, and hex stock in them.


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## GrayTech (Oct 24, 2019)

If the gearbox had other gears that mesh with that one you may be able to get a better ratio out of it.


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## ericc (Oct 25, 2019)

It still would be useful for cutting radii.


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## RJSakowski (Oct 25, 2019)

If you drove with a stepper motor rather than a hand crank, you could program in a nice round number for your gear ratio.  At eight microsteps/step it would take 93 microsteps to move the table 1º.  Actually 93-1/3 so you would never be in error by more than 12 seconds of arc.

An Arduino, a stepper, driver, and a power supply and your set.  If you picked your parts carefully, it could be done for less than $50.


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## pontiac428 (Oct 25, 2019)

One could cut a spur gear with 40 teeth for that 40:1 ratio, but I doubt it makes any difference in the universal world of mathematics.  Multiples with more prime factors will give more flexibility.  21:1 is 7*3*3, which does not have a 2*2=4 factor.  That will limit you for sure, but 12:1 or 20:1 or 24:1 sure has a lot of workable indexing options.  Any ratio that goes into 360 evenly (1, 5, 30, 40, 180, whatever) is a good candidate for a simple degree wheel RT, without need for indexing plates.

I think the backlash compensation scheme on my Kamakura RT would work well against that worm gear.  The gear would be bored and shafted on one side to work your handwheel.  Against the opposite side, a simple plunger and spring would force the worm gear toward the handwheel side to squeeze the backlash out of the gear pair.  You'd have to look at some pics of various RTs to make sense of what I said, but I think those parts are suitable for it if the OP were to pursue the idea further.


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## benmychree (Oct 25, 2019)

Why not just buy a 40:1 ratio set of worm and gear from your local bearing house or online stock gear source?


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## Jan the man (Oct 25, 2019)

Hi all
www.surpluscenter.com 1-800-488-3407 has gear reducers for as low as $69.00! Some are 20:1 and some are 50:1 At at a higher price.
Hope that helps>


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## Meleon69 (Oct 25, 2019)

The worm gear was just something I remembered I had after robbing parts off the old blower. I do actually have a box of stepper motors and a couple of arduino  kicking around


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## hman (Oct 30, 2019)

RJSakowski said:


> One revolution of the worm advances the gear one tooth.  21 teeth so 21:1.  That would be an odd number for an RT. Also an RT usually has a mechanism for taking up any slack to reduce backlash.  This would be hard to accomplish with your gear set.  However, if you are willing to do the math and only turn the table in one direction for its final setting, it could work.


I'm pretty sure it's 22 teeth, not 21 (counted twice, just to be sure).  Nevertheless, it would still be an unusual number for an RT.


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## Tim9 (Oct 30, 2019)

Yep ....that’s 22 teeth.


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## Meleon69 (Oct 31, 2019)

I’m a step closer. I’ve got my mill home.


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## Meleon69 (Nov 11, 2019)

I've just pulled the trigger on a 3 axis DRO for my mill. Aliexpress 11-11 sale. 
Should I decide to proceed with the rotary table it should help out a little. But on the flip side it might make necessity a little less. 

Before I had the lathe I thought I knew of a million things I would make if only I had a lathe. Got the Lathe and thought seems everything I want to make on the lathe would be better if only I had a mill... now I'm stumped. Seems the only things I can think of to make is more tooling for the lathe and mill. lol I'm soon gonna have to show the wife these things are useful


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## Jan the man (Nov 13, 2019)

Lots of luck on that!

JTM


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## MontanaLon (Nov 13, 2019)

Meleon69 said:


> I've just pulled the trigger on a 3 axis DRO for my mill. Aliexpress 11-11 sale.
> Should I decide to proceed with the rotary table it should help out a little. But on the flip side it might make necessity a little less.
> 
> Before I had the lathe I thought I knew of a million things I would make if only I had a lathe. Got the Lathe and thought seems everything I want to make on the lathe would be better if only I had a mill... now I'm stumped. Seems the only things I can think of to make is more tooling for the lathe and mill. lol I'm soon gonna have to show the wife these things are useful


I also invested in the same dro. I've got a wife who doesn't pay attention to the details. That is really helpful when a new gun follows me home. If she notices at all she assumes I've always had it. And if she asks I tell her "that's my rifle/shotgun/pistol" and she never asks how long I've had it. 

I am skating on thin ice there though as she has started to question why all of my guns used to fit in 1 safe and now occupy 2.


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## brino (Nov 13, 2019)

A little off-topic, my apologies to the OP....



MontanaLon said:


> I am skating on thin ice there though as she has started to question why all of my guns used to fit in 1 safe and now occupy 2.



hmmmmm............let's see if we can come up with some creative answers.....
1) the safe is shrinking with age/humidity.
2) the pistols do not get along with the rifles and I had to separate them.
3) the anit-rust coating on the rifles is turning the pistol grips funny colours.
4) don't want all my eggs in one basket.

Now back to the regularly scheduled thread......

-brino


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