Vertex (V4?) Rotary Table

[Howard LewisParticipant @howardlewis46836]

Thank You Michael.

Haven't read it all through, but it seems that my guess of 19 and 20 was what was used originally.

At CAV, in the mid 60s, we regarded Simms Motor Units as being a poor relation with lower standards, Certainly what i saw of the Minimec vs the NN type, in the 70s, it was a more cheaply made device. And in my experience, of much lower quality. I had to make a couple of unannounced visits to Finchley to sort out problems that should never have happened.

Hopefully Martyn will be able to make up a set of parts that will perform as required to put bhis car back on the road again.

Howard.

Edited By Howard Lewis on 20/01/2021 21:39:22

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Howard Lewis on 20/01/2021 21:38:12:

Thank You Michael.

Haven't read it all through, but it seems that my guess of 19 and 20 was what was used originally.

[…]

.

… I didn’t realise it was a guess, Howard … Well done !!

MichaelG.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi MichaelG, not that I hold that much interest in the subject, but thanks for the link as it helps to understand the goal Martyn is aiming for, and no I haven't read the whole thing, but have got the gist of the coupling's Vernier reason.

Regards Nick.

[JasonBModerator @jasonb]

Though I'm still none the wiser why Martyn is asking about the particular angle as it won't give a whole number of teeth which to me is more critical than the exactness of the wrong angle which will result in 18 and a bit teeth

 

Edited By JasonB on 21/01/2021 08:02:01

[Michael GilliganParticipant @michaelgilligan61133]

I think only Martyn can explain his desire to set that particular angle

… very clearly specified [but with no contextual reference] in the opening post.

MichaelG.

[SillyOldDufferModerator @sillyoldduffer]

I make so many mistakes doing sums I've become expert at backtracking to find where I went wrong. Always involves bad language.

Only Martyn can confirm, but I think he went astray doing the h:m:s sum

360/19 = 18.947

19 – 18.947 = 0.053 (The difference needed to calculate minutes & seconds)

0.053° = 3'12"

The slip was adding 3'12" to 19 rather than subtracting it.

Post mortems are interesting but too late to save the patient!

Dave

[JasonBModerator @jasonb]

That is what I said back on the 17th

"Could there be a link as you mention 18.947deg which is just about 0,3', 12" short of 19deg"

[SillyOldDufferModerator @sillyoldduffer]

Posted by JasonB on 21/01/2021 09:45:16:

That is what I said back on the 17th

"Could there be a link as you mention 18.947deg which is just about 0,3', 12" short of 19deg"

Doh! Of course you did…

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, well for what it's worth, here is my calculation; d denoting degrees.

19 x 4d = 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.

Please don't hesitate to correct me, if you think it is wrong.

Regards Nick.

Edited By Nicholas Farr on 21/01/2021 10:50:41

[Michael GilliganParticipant @michaelgilligan61133]

Here’s the elastomeric element … for a Chipmunk !

**LINK**

https://www.ebay.co.uk/itm/84326-Chipmunk-aircraft-Vernier-Coupling/153974750149

MichaelG.

.

Edit: __ and a recently completed listing for one of the Austin 7 metal components:

https://www.ebay.co.uk/itm/Vintage-Austin-7-Simms-Magneto-Vernier-Coupling-/333817291042

Edited By Michael Gilligan on 21/01/2021 11:06:02

[John PParticipant @johnp77052]

Going back to the OP original question .

"I'd now like to move the table through minutes and seconds
( to be precise 19° 3' and 12". I can't work out how to do this.
Could someone please talk me
through it in a Pooh-Bear-of-Little-Brain-speak?"

I think there is little doubt from the many replies that there
would be a slim chance of obtaining an accurate position
of 19° 3' and 12" simply because of the mechanical errors
within the rotary table and also being able to count using
the existing hand wheel set up would be difficult to keep track of .
As has been mentioned before the stepper motor route would
be most likely to be able to count with some accuracy.

My own cnc rotary table has a worm and wheel ratio of 75 to 1
and connects to the stepper motor with a toothed belt ,as part
of some alterations which included regrinding the morse taper
some additional drive pulleys have been made, these also
have some secondary functions on some other machines.
In doing this the rotary table can be between 75 to 1 ratio
and 142.5 to 1 with the pulleys that i have at this time.

Just playing around with numbers on this table using a 10 tooth
pulley on the stepper motor and a 72 tooth driving the worm
would make the table 540 to 1 ratio in whole step (200)would equal
108000 steps per rev .Since there are 1296000 seconds
in 360° divide by 12 to equal 108000,so a single step now
equals 12 seconds . 19° 3' 12" = 68592 seconds divide
by 12 for 5716 motor steps .

It is unlikely the rotary table will be accurate but at least
the count will be correct.

For a 90 to 1 table the 72 tooth pulley is changed to
60 tooth for the same count.

Probably too much work to set up if you don't already have
something like this already.

John

[Martin ConnellyParticipant @martinconnelly55370]

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

[HopperParticipant @hopper]

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.

[HopperParticipant @hopper]

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 x° '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 FarrParticipant @nicholasfarr14254]

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.

Regards Nick.

[Martin ConnellyParticipant @martinconnelly55370]

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

[Anonymous]

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:

and:

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

[JasonBModerator @jasonb]

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.

[HopperParticipant @hopper]

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 FarrParticipant @nicholasfarr14254]

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 LewisParticipant @howardlewis46836]

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

[Anonymous]

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. I had to make my own:

Andrew

[Michael GilliganParticipant @michaelgilligan61133]

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:

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.

[HopperParticipant @hopper]

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. I had to make my own:

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.

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.

 

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

[HopperParticipant @hopper]

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.

[Author]

Posts