# Rotary Table minutes seconds



## Goldigger (Aug 8, 2011)

I'm stuck on how to work out how many turns of the handle on my vertex 4inch rotary table..
I understand that my gear ratio is 90:1 so 90 turns of the handdle will rotate the table through 360 degrees, one turn of the handle is 4 degrees
I want to cut 16 slots in the ali as shown in the picture below, so far i have cut 8 slots. I found my starting point and cut the first slot then rotated the handle 11.25 turns, to cut 4 slots its 90/4 = 22.5 turns so 8 is 11.25. 
Now i want to cut another slot which would be every 5.625 turns of the handle..half of 11.25







How do i work that out using the minutes and seconds? can someone explain whats what on the scale please?
My understanding of it is 0-1-2-3-4 4 degrees split into 60 mins, 30 min mark in the middle of 1 degree





Thanks


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## Maryak (Aug 8, 2011)

Griz,

Try this link http://cdn0.grizzly.com/manuals/h7527_m.pdf

Section 3 - Operations

Gives a very good explanation of the minutes and seconds operation.

Hope this helps

Best Regards
Bob


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## Goldigger (Aug 8, 2011)

Thanks for the replies guys, sorry for not being clear..
I cut the the first 4 slots by turning the handle 22.5 times each, then turned the handle 11.25 times to start another set of 4 slots
To start my next set of 8 slots that would be half of 11.25 = 5.625 turns.
I was having trouble translating the .625 turns, but as there is 240 mins around the dial 240/100*.625=150mins
so 5 turns and 150mins on the dial...
Hope that makes sense..


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## steamer (Aug 8, 2011)

I know what you mean Goldigger.

Hope this helps turns are absolute turns, not incremental.






Dave


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## Maryak (Aug 8, 2011)

Yes,

Makes sense to me.

Bob's way.






Best Regards
Bob 

View attachment Vernier.pdf


View attachment Vernier1.pdf


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## Goldigger (Aug 9, 2011)

steamer  said:
			
		

> I know what you mean Goldigger.
> 
> Hope this helps turns are absolute turns, not incremental.
> 
> ...



Dave i like the look of your spreadsheet, any chance of a copy please?

Thanks
J


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## steamer (Aug 9, 2011)

Send me a PM with your email..

Dave


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## electrosteam (Aug 10, 2011)

J,
I have a 6 inch Vertex that has got an incorrectly engraved scale on the vernier.
It was very perplexing until I twigged to what the problem was.
I am away from home at the moment, so I cannot be more specific, but I know it was easy to allow for the errors once I became aware of them.
The error was something like the full range of the vernier not matching one division on the main scale.
The photo on your scale seems correct.
Just read the posts on how to read the vernier, then carefully check the actual graduations.
Mine may be a rare occurrence, but !!

John.


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## Goldigger (Aug 10, 2011)

Cheers for the words of warning John...I think my is ok, I have a good eye for when somethings out a bit..

Here's a pic of the extra grooves to show what i was trying to achieve..


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## Maryak (Aug 10, 2011)

electrosteam  said:
			
		

> The error was something like the full range of the vernier not matching one division on the main scale.



John,

When I started to make the drawings and pdf's for my post. A bit of research revealed the vernier ratio is 9/10ths of the main scale.

If we take the minutes as the main scale there are 240 around the dial. 9/10 is 216/240 which reduces down to 27/30 and that's what I have on my vertex 6" table from the 60sec on the left to the 60sec on the right. At 0/0 alignment the 60/40/20sec divisions align with nothing as the 60sec are at +/- 13.5 mins or they cover 27 minutes of the minute scale. I hope my interpretation is valid.

Best Regards
Bob


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## electrosteam (Aug 11, 2011)

Bob,
you may be correct, but I am not sure.
The 9/10 effect is something like what I observed.

I thought the vernier should span 10/10 of a the main scale.
That is, the 120 seconds of vernier spans main scale graduation to main scale graduation = 2 minutes.
The 6 graduations on the vernier then represent 20 seconds each.

I am away from my workshop working in the field, back mid September.
I will have to review my thinking when I get home.

Not much progress from me, but others may be more helpful.
John.


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## electrosteam (Aug 12, 2011)

Bob,
Living in an apartment 1500 km from home gives one time to think !

The 9/10 factor does not apply to the rotary table scales.
This factor applies when the primary scale is divided into 10 parts by the vernier.
Each vernier division is 9/10 of the main division.
A movement of 1/10 main division from the 0 main mark will align the first vernier mark with a main mark.

For the rotary table, there are 6 vernier divisions and 2 minutes per division on the main scale = 2/6 minutes = 20 seconds per vernier division.
The factor here is 5/6.
The vernier length is 11 minutes, so 6 movements of the vernier advances it 6 x 20 = 120 seconds = 2 minutes = 1 main division.

The rotary complicates the situation by placing the 0 vernier mark in the middle and having +/- vernier divisions.
Try using it with the -60 mark read as 0 seconds, the 0 mark read as 60 seconds and the +60 mark read as 120 seconds

The general rule is that for a vernier of N divisions the vernier spans N-1 main divisions.

For an ordinary imperial vernier caliper, the main divisons are 0.025 inch, the vernier divides by 25, the vernier scale spans 24 main divisions = 24 x 0.025 = 0.6 inch.
The factor is 24/25.

Modern imperial decimal vernier calipers have the vernier of 25 divisions spanning twice that required ( = 1.2 inch ) for convenience with the vernier marks aligning with every second main mark.

Fractional imperial vernier calipers read to 1/128 inch where the main division is 1/16 inch and the vernier was 8 divisions. The vernier scale spans 7 x 1/16 inch of the main scale.
The factor is 7/8.

John


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## mklotz (Aug 12, 2011)

> The general rule is that for a vernier of N divisions the vernier spans N-1 main divisions.



Exactly. While this reduces to the 9/10 observed in a purely decimal vernier, the 9/10 factor is not generally true.


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## Maryak (Aug 12, 2011)

John,

Thanks for taking the trouble to give such a comprehensive explanation of Verniers various. :bow: :bow:

Best Regards
Bob


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## electrosteam (Aug 17, 2011)

Bob,
my comment about modern imperial verniers being double length is not quite correct (thinking lapse !).

The vernier is actually (2N-1) x main scale units.
This is the normal (N-1) main scale units for the standard vernier + N main scale units to double the scale length.
So the imperial double length is (2 x 25 - 1) * (0.025) = 1.25 inch - 0.025 = 1.225 inch.

For those interested in details, hope this helps.

regards from sunny Queensland,
John.


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