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Vertex (V4?) Rotary Table

How to measure minutes and seconds

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Martin Connelly21/01/2021 22:44:35
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Nick, use a calculator with a D°M'S button, it's much easier. 360/19 = 18.94736842 press D°M'S and get 18°56'50.53

Or if you do not have this function on a button (some numbers are rounded):

18.94736842 - 18 = 0.94736842 note 18 is degrees

0.94736842 x 60 = 56.8421 note 56 is minutes

56.8421 - 56 = 0.8421

0.8421 * 60 = 50.5263 note this is seconds

so 18° 56' and 50.5263"

Martin C

Hopper22/01/2021 02:49:02
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Why wouldn't you just use a set of indexing plates to obtain 19 divisions and do away with minutes, seconds, microns, quarks and parsecs? Well worth purchasing if you have a rotary table. Nobody faffs about with degrees to cut gears and splines, surely?

Or you could use a 19 tooth gear as an indexer with a jury rigged plunger etc. Or even the readily available new rubber toothed insert for the Simms magneto coupling itself, with a bit of care.

Or you could make up a Sparey-style banjo plate that fits on your rotary table and uses a train of your lathe's change gears and an indexing plunger to obtain an almost endless possible number of divisions using compound gearing. But with the low cost of those Indian/Chinese index plate sets these days hardly seems worth the effort.

Hopper22/01/2021 03:00:02
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Posted by martyn nutland on 18/01/2021 12:22:05:
...
 
Yes. This is still about the Simms vernier and I have come to Howard's conclusion that 20 'teeth' on one side of the coupling and 19 on the other is a solution that is simple and will make no difference to the performance. Or 20 teeth on one side and 20 on the other 'out of sync', as it were, with the first row, i.e. slightly stepped one side to the other.
 

Wouldn't you make it to fit the new Simms Coupling rubbers that are sold by Austin 7 suppliers etc? Which I believe are the 19/20 combination.

Making a 20/20 combo with the teeth offset on one side will not give you the incremental vernier adjustment the 19/20 does. Each tooth on the 20/20 will be offset to its counterpart on the other side by the same amount, so rotating the rubber by one tooth will always give exactly the same alignment. With the 19/20, each rotation by one tooth on one side gives a gradually increasing cumulative effect on the other so you can move it by one tooth for a small adjustment or say 5 teeth for a bigger adjustment.

That's how a vernier scale on vernier calipers, or your rotary table, works. The extra vernier scale of 10 lines has the 10 lines occupying the same distance as 9 lines on the main measuring scale. It is this 9/10 combo that provides the vernier effect. Hard to explain without drawings but you can google it.

Edited By Hopper on 22/01/2021 03:03:48

Nicholas Farr22/01/2021 07:33:07
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Hi Martin Connelly, I don't have a calculator with a D*M button and I did the calculation in a way that I thought most people would understand and be able to follow, I was not in such a rush to get a instant answer, but to show proof of the answer.

A bit of maths even with the assistance of a calculator, is always good for the old grey cells, anyway. smiley

Regards Nick.

Martin Connelly22/01/2021 08:35:46
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Nick, I have got 2 A levels in maths and an engineering degree and I got lost at the first line, 19 x 4d = 342d

Martin C

Andrew Johnston22/01/2021 09:24:18
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Posted by Hopper on 22/01/2021 02:49:02:

Nobody faffs about with degrees to cut gears and splines, surely?

Oh dear, that must mean I'm a nobody:

final drive gear cutting.jpg

and:

internal gear cutting.jpg

Fortunately the large spur gear was 72 teeth, so 5° per tooth, and was too big to fit under the spindle of the horizontal mill. For the internal gear the setup was the best for countering the slotting forces.

Andrew

JasonB22/01/2021 10:04:01
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I would expect a lot of people faff about if the number of divisions they want is not available from the plates or knowing a lot of ME's they are too tight to buy or make plates. Like Andrew if it's a nice whole number I just use the handwheel rather than waste time setting up plates.

Hopper22/01/2021 10:09:55
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5197 forum posts
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Fair enough for a standard 5 degree tooth I suppose. But getting down to minutes, not so much. Guess I was spoilt with a being able to just walk to the tool crib and get an index plate to suit.

And I suppose for a beginner, coming to grips with the vagaries of index plates and fingers is no simpler than dealing with the vernier scale on the rotary table handle. Either way is fraught with opportunity for a careless slip over many repeat movements.

Edited By Hopper on 22/01/2021 10:11:56

Nicholas Farr22/01/2021 10:38:20
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Hi Martin Connelly, I sorry you got lost, there is of course one aspect wrong my calculation and that is the 18 whole degrees that is the result of 360/19, so;

360/19 = 18.94736842. Therefore 18d x 19 = 342d.

360d - 342d = 18d. 18d x 60 x (60) = 64800"/19 = 3410.526316", then cutting to the chase, 56' = 3360".

3410.526316 - 3360" = 50.526316". Therefore it is 18d 56' 50" to the absolute best setting I could make in my last photo.

I had mistakenly submitted the 4d for each turn of the handwheel instead of the 18d from 360d/19 divisions, but my calculation was done correctly and the answer is correct. I think I got muddled with using an index plate V's degrees.

Thanks for bringing it to my attention.

Regards Nick.

Edited By Nicholas Farr on 22/01/2021 10:48:47

Howard Lewis22/01/2021 10:59:59
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8 photos

An EXCEL spreadsheet will contain a LOT of cells with numbers for partial holes, but the whole numbers will show what plate and hole circle to use, if a chart does not show it..(I highlight them )

Occasionally some numbers are so close that a whole number that the error may be negligible after the reduction ratio is taken into account (10.04 holes on a 39 hole plate, springs to mind, putting the error into the 4th place of decimals with a 90:1 ratio! )

Adding a new number of divisions simply entails inserting another line in the right place and looking for a cell with a whole number.

One day I must get round to making up an extra plate or two with the missing numbers of holes to extend the range of possible divisions.

The risk is of getting into the spiral of making Division Plates to make Division Plates!

Howard

Andrew Johnston22/01/2021 11:22:50
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Posted by Hopper on 22/01/2021 10:09:55:

Guess I was spoilt with a being able to just walk to the tool crib and get an index plate to suit.

Lucky you. smile I had to make my own:

Dividing Plate

Andrew

Michael Gilligan22/01/2021 11:33:18
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Now that we are aware that Martyn’s opening question was based upon a false premise, and he actually wants 19 ‘teeth’ on a plate, to engage with an elastomeric coupling ...

Here is a template for the indexing:

58b4c156-bf04-48c6-ac40-926fccb3628b.jpeg

Even as a paper print from a jpeg file ... it is probably adequate for the purpose.

Just cut a suitable size circle and stick it to the handwheel on the rotary table ... the worm reduction will even things out.

This has been an interesting, but largely irrelevant discussion.

MichaelG.

Hopper22/01/2021 11:39:31
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Posted by Andrew Johnston on 22/01/2021 11:22:50:
Posted by Hopper on 22/01/2021 10:09:55:

Guess I was spoilt with a being able to just walk to the tool crib and get an index plate to suit.

Lucky you. smile I had to make my own:

Dividing Plate

Andrew

Haha. I've done that too. All 812 holes in three plates for the Fabricated Versatile Dividing Head. After trepanning the three discs out of 5mm flat plate. Then there was the 812 holes to be deburred both sides. Never again.

dscn3006.jpg

At least with GHT's micro-adjustment second worm mechanism, holes can be drilled, or gear teeth cut, to any number within a thousandth of a degree resolution. clearly indicated on the second worm's graduated handwheel and needing only a 60 hole circle to thus generate the three plates from scratch, or a 127 conversion gear or your 19 spline Simms Coupling. He was a darned cunning operator the old GHT.

dscn2969.jpg

 

Edited By Hopper on 22/01/2021 11:50:17

Hopper22/01/2021 11:42:48
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Posted by Michael Gilligan on 22/01/2021 11:33:18:

This has been an interesting, but largely irrelevant discussion.

MichaelG.

Not irrelevant. Remember there is always more than one technique for removal of the feline epidermis.

Michael Gilligan22/01/2021 11:54:01
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17328 forum posts
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Largely irrelevant, in respect of the ‘seconds’ precision to the job in hand.

MichaelG.

Nicholas Farr22/01/2021 14:34:15
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Mi MichaelG, largely irrelevant, but the O/P did ask how to set about his problem with his minutes and seconds, and maybe now he can understand that chasing a few seconds on the set up he has, is somewhat futile.

Regards Nick.

Howard Lewis22/01/2021 14:49:21
4448 forum posts
8 photos

Am I the only one to think that after all our discussions the OP is going to use Division Plates on his Rotary Table to produce the required 19 and 20 divisions (as the original coupling )?

Howard

Michael Gilligan22/01/2021 14:51:02
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I’m frequently ‘judged’ by the people who think mentioning ‘Angels on pins’ is clever ... so I thought I should be the one to mention that most of this discussion was irrelevant to Martyn’s actual requirement [as opposed to his perceived one].

Ho Hum

MichaelG.

Jon Lawes22/01/2021 14:51:23
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471 forum posts

Back when I went to the pub most of the conversations were irrelevant, but still very enjoyable and often enlightening.

Michael Gilligan22/01/2021 14:53:29
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17328 forum posts
787 photos
Posted by Howard Lewis on 22/01/2021 14:49:21:

Am I the only one to think that after all our discussions the OP is going to use Division Plates on his Rotary Table to produce the required 19 and 20 divisions (as the original coupling )?

Howard

.

Does Martyn have any Division Plates, Howard ?

... I don’t recall him mentioning them.

[ which is why I provided one for him to print ]

MichaelG.

Edited By Michael Gilligan on 22/01/2021 14:57:54

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