# Rotary Table



## Jack (Oct 31, 2007)

Yes I have a rotary table. If you have a look at the webster plans (page eight) you will see the exhaust cam that I need to make. I have already turned the blank to .712 on the end of a small chunck of steel and drilled and reamed the .375 bore but now I'm stumped.
Any help that you could give me is certainly appreciated, Just rember that I am old and slow and not the sharpest knife in the drawer.


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## Hilmar (Sep 25, 2008)

I am a bit puzzled over a 7.5" Rotary table I have. 
It was made by John B Stevens, NY, NY .

The table has 360° and the fine adjustment ( the Crank ) has 225 Dev. It takes 
2 turns (450 Div. to move 10°.
What I am missing??
Hilmar


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## carbide_burner (Sep 26, 2008)

> What I am missing??



Excellent qeustion! 

 ??? What am I missing?? ???


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## Lew Hartswick (Sep 26, 2008)

That makes 16200 div per 360 deg. Now thats a bit odd. How about a picture or two?
  ...lew...


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## Bill (Sep 26, 2008)

Maybe I'm missing something, but isn't 10 deg/450 divisions = 1 min 20 sec per division? 
One turn = 5 deg/225 = .02222 deg/division or 1' 20" converted to DMS format.

Bill


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## Bill (Sep 26, 2008)

What I meant to add: 5 deg per turn would equate to 72 turns of the crank for a full 360 degrees. A 1:72 ratio.

Bill


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## Hilmar (Sep 26, 2008)

> What I am missing??



What I was asking or trying to bring across, is this not an od ball division on the crank? I am not familiar with rotary tables.
Would be kind of hard to use in the shop. 1° = 45 Divisions.
Hilmar


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## BobWarfield (Sep 26, 2008)

I tried a bunch of ratios and some Googling to find some rhyme or reason. No avail.

Look into one of John Stevenson's excellent electronic controls for it. You slap a stepper motor on it, and this magical little box let's you dial in anything you want, hit a button, and it goes there.

Best,

BW


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## wareagle (Sep 26, 2008)

I don't have a clue.  ???

So I went to my _resource_ to ask the question (he's an old crusty machinist that was in the trade for 50 years) and his response was, "I have never heard of such bull$!*^." He followed up with some colorful language that I can't post here, but all that to say he didn't know, either.  This is the first time he hasn't known an answer or pointed me in a direction to a question I have asked. I have to say that surprised me!

You may have a real odd ball there. I am interested to see what comes of this.


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## John S (Sep 26, 2008)

So it's a 72:1 table, not all that uncommon but what is uncommon is the markings on the handwheel which are unusual.

I don't have any experience on this but I wonder if it's been done as a special for some application, marking gun sights which don't always follow a standard in degree's ? I recall the application of a mill [ no typo ] here somewhere.
As I say I have no experience of this sort of thing , never having progressed beyond throwing bricks.

As a side note I do convert quite a few tables to stepper application and some are 72:1, the original handwheels are removed and thrown as they clutter up the place. Next time I get a batch [ usually every 3 to 4 weeks ] I can save a handwheels marked in degrees if you want to convert it ?

.


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## Lew Hartswick (Sep 26, 2008)

John Stevenson  said:
			
		

> I recall the application of a mill [ no typo ] here somewhere.
> .



I take you mean the "artillery mill" . That is 64000 per rev. They just couldn't handle 2 Pi with the 
kind of people doing the artihmetic. 
  ...lew... (the mill in this case is meant to be a "milliradian")


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## mklotz (Sep 26, 2008)

Lew Hartswick  said:
			
		

> I take you mean the "artillery mill" . That is 64000 per rev. They just couldn't handle 2 Pi with the
> kind of people doing the artihmetic.
> ...lew... (the mill in this case is meant to be a "milliradian")



Make that 6400 per revolution or 0.05625 deg/mil. A milliradian is 0.05729 deg.


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## John S (Sep 26, 2008)

So not an artillery mill, Oh well another flat battery in the car park of life - sigh :-\

.


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## kvom (Sep 26, 2008)

FWIW, each division is 80 seconds of arc.


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## John S (Sep 26, 2008)

kvom  said:
			
		

> FWIW, each division is 80 seconds of arc.



That's handy if you are on overtime.

Well went to dig out that toolpost for CrewCab and fell over these.







Both sizes of the ones I do in 72:1
5 degrees per turn, larger one is 2 3/8" diameter with 10mm bore and the smaller is 2" diameter with 8mm bore.

Any good ?
.


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## Hilmar (Sep 26, 2008)

Hi John 
  the 2 3/8 would fit perfect, That is the size on the table.
 If it is still available what is it you need from me?
Hilmar


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## John S (Sep 26, 2008)

Hilmar  said:
			
		

> Hi John
> the 2 3/8 would fit perfect, That is the size on the table.
> If it is still available what is it you need from me?
> Hilmar



Your Tardis interface number 

Seriously, PM or email me your snail mail address and I'll get it in the post to you.
.


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## Nick Hulme (Oct 9, 2008)

John Stevenson  said:
			
		

> So not an artillery mill, Oh well another flat battery in the car park of life - sigh :-\
> 
> .



Artillery - Battery, ;D
I think you slipped that one past 'em, 
Nick


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## Richard1 (Feb 13, 2009)

I have been given a 12inch rotary table but sadly the worm and the eccentric sleeve it runs in are missing. The table seems to be almost new with no visible wear and seems to be very good quality. There is no makers name. The worm wheel has 90 teeth. So where do I start in either making or buying a new worm for it? 

Richard1


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## cfellows (Feb 13, 2009)

You first need to determine the diametral pitch of the worm gear. You can approximate this by diving the diameter in inches by the number of teeth on the gear.

In that size table, the pitch is probably around 10 or 12 or 16. For example, a 10 pitch worm gear with 90 teeth would be 9 inches in diameter. A 12 pitch would be 7.5 inches diameter. A 16 pitch would be 5.625 inches.

Once you know the pitch, you can determine the worm turns-per-inch by dividing the diametral pitch by PI which is 3.14159. So, a worm gear with a diametral pitch of 12 would require a worm with 3.82 turns per inch. A 16 pitch worm gear requires a worm with 5.09 turns per inch (5 would probably work OK).

You also need to know the pressure angle of the worm gear, although it is most likely 14.5 degrees.

You could make one, but you will need a lathe with thread turning capability and you might need an odd assortment of change gears to get the fractional number of turns per inch.

You might also be able to use ACME threaded rod if you can find the right thread pitch. It won't match the worm tooth profile exactly but it might be close enough.

Chuck


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## Richard1 (Feb 13, 2009)

I guess it is 12 DP but will check when I go out to the shop in the morning. Just had a thought that it might be Module as the hole for the bearings it should run in is 40mm. Will let you know anyway.


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## Mainer (Feb 13, 2009)

A lot of bearings are metric, even if everything else is in inches, so I wouldn't take that as any particular indication one way or the other.


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## Richard1 (Feb 20, 2009)

Thank you the work proceeds well. I am working on the eccentric bearing that will carry to worm at the moment. Seems to fit the table perfectly without shake now I just have to bore it and make up the mounting for the division plates. Should be a good table when it is all fixed.


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