# How to read this rotary table vernier scale



## clevinski (Sep 19, 2013)

Hello, All,

I recently bought an inexpensive, 4-inch rotary table for use with my mini-mill.  While I learned to read a vernier scale when I was about 12, this one has me stumped.




Each  division on the moving dial is 5 minutes (12 divisions between  degrees, 60 minutes/degree, 60 / 12 = 5 minutes).  But how to read the vernier?  There are + and - six  increments, so I think the total range is dividing the 5 minutes of each graduation of the moving dial into 12 parts, or .4166667 minutes per graduation.  That happens to  be 25 seconds per graduation, but so what?  If you get alignment with either of the "60" marks on the vernier,  that would be 2.5 minutes.  But what about the others; why the very odd value?  And why is the  2.5 minute mark on the vernier labeled "60"?

Something tells me that each vernier division should be 0.5 minutes, but damned if I know why, or if that's true.

Any help would be greatly appreciated.  Thanks, guys!


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## Tony Wells (Sep 19, 2013)

I'd say the Vernier indicates 10 sec divisions.


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## clevinski (Sep 19, 2013)

Tony Wells said:


> I'd say the Vernier indicates 10 sec divisions.



Hi, Tony...

Well, if that were the case, then you wouldn't be able to resolve the reading, (I *think!*).

For example, suppose I'm between two of the moving graduations.  This means that I have the reading to within 5 minutes, the resolution of the moving graduations.  Now I want to resolve where I am between two 5 minute lines.  If the vernier only had 10 second divisions, then it would be able to resolve +/- 60 seconds, or +/- 1 minute.  But the space between the moving graduations is *5* minutes; +/- 1 minute still leaves me not knowing where I am.

I feel stupid, like this is obvious and I'm just missing something...


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## Tony Wells (Sep 19, 2013)

Yeah, disregard my earlier post. I took a look at the larger picture. Not 10 sec grads. Now I still can't see for sure, but I have a theory. One side of the 0-60 could be the even minutes of the 1-5 of the dial grads, and the other side the odd minutes. I can't say I remember ever seeing that layout on a vernier, but there's a lot in life I haven't seen. Being that the dial is in 5 minute grads, the next smaller grad should be to break down those markings. There can't be any seconds marks on that I think. This is just a theory though. You could try to see if the 60 mark lines up on one side of the vernier but not the other, then the next mark that lines up is on the other side.


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## clevinski (Sep 19, 2013)

Tony Wells said:


> Yeah, disregard my earlier post. I took a look at the larger picture. Not 10 sec grads. Now I still can't see for sure, but I have a theory. One side of the 0-60 could be the even minutes of the 1-5 of the dial grads, and the other side the odd minutes. I can't say I remember ever seeing that layout on a vernier, but there's a lot in life I haven't seen. Being that the dial is in 5 minute grads, the next smaller grad should be to break down those markings. There can't be any seconds marks on that I think. This is just a theory though. You could try to see if the 60 mark lines up on one side of the vernier but not the other, then the next mark that lines up is on the other side.



Hi, Tony,

Well, the more I think about it, the more I realize that they are 25 seconds / graduation on the vernier, and the vernier being labeled "60" on either side is really irrelevant.  With 6 graduations on either side of the zero, that's 12 graduations total.  12 graduations x 25 seconds/graduation = 300 seconds; 300 seconds / 60 seconds/minute = 5 minutes, the value of a single graduation on the moving scale.

That's not terribly convenient, but that's what the math works out to...

Thanks for your help!


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