Rotary Table Scales

[martyn nutlandParticipant @martynnutland79495]

How do you set the degree scales on a Vertex rotary table

[martyn nutlandParticipant @martynnutland79495]

I wonder if someone who is familiar with rotary tables could explain to me how to read/operate the degree scales.

 

I have a 150mm diameter Vertex model. It has a 360° scale around the table and a randomly (I presume) placed pointer on the fixed base.

 

Working in from the hand wheel, there is a knurled ring that looks separate from the hand wheel but won't rotate without it. Integral with the knurled ring there is a scaled cylinder – rather like the markings on a lathe. But these are engraved 0 – then 15 divisions on – 30 – then another 15 division on – 1, and so on until you pass 3 and come back to zero after a full revolution of the hand wheel. Thus, I assume each of the 15 divisions between 0 and 30 represents two minutes and the 1 represents 60 minutes or one degree of table movement or four degrees per revolution of the hand wheel i.e. a ratio of 90:1 in terms of wheel to table revolutions.

 

After the aforementioned knurled ring and cylinder there's another stepped cylinder that turns independently of the outer one. This is engraved, at random as far as I can see, with a scale 60 0 60, with three divisions to the left of the zero and three to the right. I assume these are seconds of one minute of one degree. Protruding vertically from the after part of this cylinder is a short lever that engages or disengages the worm drive to the table so you can turn the latter by hand, if so wished, without turning the hand wheel. A thumb screw on the body of the machine locks the worm in engagement.

 

By way of example of my frustration: If I want a bolt circle of three, what I would do is twirl the hand wheel until the pointer on the fixed base registers with zero on the annular ring on the bottom of the table. Then, twirl again to 120, do the business, twirl another 120 (240 on the scale) and so on. But this strikes me as very unsophisticated and negates the point of all the gubbins behind the hand wheel. So, anybody, how do you set it up to do, for the sake of argument, a segment of 60° 12' 30"?

 

Thanks in advance for any guidance. Martyn

 

[John FieldingParticipant @johnfielding34086]

Does the item not come with a users manual? I would have thought that would be a good place to start.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Fielding on 20/03/2016 14:00:25:

Does the item not come with a users manual?

.

This one, from Grizzly looks appropriate.

MichaelG.

[JasonBModerator @jasonb]

Your 0-1-2-3-0 scale should be adjustable by loosening a grub screw.

So set table so the 0 is near as possible to te marker, then loosen handwheel scale and set 0 to line up with the 0 on the 60-0-60 scale.

60deg is 15 full turns

12mins is 6 divs on the 0-1-2-3-0 scale

30 mins is part way between the 20 second and 40 second veneer marker

So after 15 turns your 12div line needs to sit between just past zero and two othe lines set equally to the 20 & 40 vernner lines

[Howard LewisParticipant @howardlewis46836]

As has been said may times; if all else fails, read the Instructions; assuming that you have, or can access, them.

The 60-0-60 scale, surely is a Vernier scale to improve the resolution of the angular division.

(Not that the Vertex manual refers to the Vernier scale. It just assumes that you know what it is and how to read a vernier).

The Vernier scale allows you to move the Handwheel in small increments,as outlined above.

The gear ratio for the Vertex HV6 Rotary table is 90:1, so 30 turns of the handle will give one third of a turn of the table, and so on, or use the degree scale on the edge of the table, so that you rotate the table the required number of degrees, (say 72 degrees, if you wanted five divisions, 60 degrees for 6 divisions, and so on).  As long as you bring the Handwheel back to the same point every time, it will give an accurate result

If you are going to use any of the three Division Plates available for the HV6, DON'T trust the chart at the back of the manual. I did, and made three scrap gears, before spending time to make an EXCEL spreadsheet, which corrected the EIGHT errors and omissions. Using the spreadsheet figures, allowed me to cut a good 13T gear.

(See my thread on this Forum on the HV6 errors. Stub Mandrel has posted the spreadsheet on his website).

Anyone having a Rotary Table, or Dividing Head with a ratio other than 90:1 has only to change the gear ratio, and the number of holes in the Division Plates, in the formulae, to have a spreadsheet for their equipment. (I HOPE!)

Howard

Edited By Howard Lewis on 20/03/2016 16:06:21

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Howard Lewis on 20/03/2016 16:00:35:

As has been said may times; if all else fails, read the Instructions; assuming that you have, or can access, them.

The 60-0-60 scale, surely is a Vernier scale to improve the resolution of the angular division.

(Not that the Vertex manual refers to the Vernier scale. It just assumes that you know what it is and how to read a vernier).

.

Hence my reference to the Grizzly manual

MichaelG.

[Roger HeadParticipant @rogerhead16992]

You may also want to look at the Grizzly manual for their H7527 RT, which also looks almost exactly like a Vertex 6", with the exception that this manual (and the one linked by Michael) illustrate a 4-slot table. My 12-year-old Vertex has only three slots. The H7527 manual also has a couple of pages on dividing, but double-check the numbers in the table before using them. It also illustrates two oiling points, one in the main body near the handwheel, and one in the side of the table. My RT also has an oil point on the top of the table near the centre hole, presumably for the main table bearing, although I have never seen it illustrated or mentioned in any docs.

As you say, the 'zero mark' tacked on the side of the main body doesn't seem to have any relationship to anything else, but as you generally need to indicate off your workpiece for alignment setups, its lack of precision matches its usefulness. I just use it for keeping track of whole degrees in my head.

Roger

P.S. The 7527 manual also has a slightly expanded explanation of the vernier scale use, with a couple of examples.

Edited By Roger Head on 21/03/2016 00:32:39

Edited By Roger Head on 21/03/2016 00:33:58

[John McNamaraParticipant @johnmcnamara74883]

Hi A while back I made up a spreadsheet to calculate the required angles for dividing. using a Vertex type Rotary Table.

Its an excel spreadsheet. Enter a number to divide and It will only show the needed settings for that number.
Handy if you dont have dividing plates

Best to print it out and mark the rows off as you do them.

(Always turn the handle one way, if you overshoot reverse well back then try stopping on the exact mark again to avoid backlash)

Link

**LINK**

Regards
John

[mark smith 20Participant @marksmith20]

Posted by John McNamara on 21/03/2016 11:58:34:

Hi A while back I made up a spreadsheet to calculate the required angles for dividing. using a Vertex type Rotary Table.

Its an excel spreadsheet. Enter a number to divide and It will only show the needed settings for that number.
Handy if you dont have dividing plates

Best to print it out and mark the rows off as you do them.

(Always turn the handle one way, if you overshoot reverse well back then try stopping on the exact mark again to avoid backlash)

Link

**LINK**

Regards
John

Hi John, how would you adapt that spreadsheet in the link for use with a 72:1 table ratio (5 degrees per turn)

Edited By mark smith 20 on 31/03/2016 14:30:14

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, forgive me if I'm missing something, but in the example in the Grizzly manual, I read it as 0 44 minuets and 20 seconds, because there are only 15 graduations in each quarter, making each graduation 2 minuets, so, 30 + 10 + 2x 2 = 44 and not 42.

A similar question to the OP was asked in this thread back in 2011 **LINK** My Vertex RT also has 2 minuet graduations.

Please feel free to correct me if I'm wrong and explain why.

Regards Nick.

P.S. my input about how to read the scale in the above link, is at the bottom of the first page.

Edited By Nicholas Farr on 31/03/2016 22:33:45

[Roger HeadParticipant @rogerhead16992]

Nick, I presume you are referring to the example in the Grizzly manual linked to by Michael (g1049_m.pdf). I agree with you, it appears that they simply counted two divisions past the 30 + 10 minute marks instead of two minutes, which would only be one division. So you are correct, their example illustrates setting to 16deg 44min 20sec, although their words say different.

If you look at the manual that I referenced (h7527_m.pdf) their examples (different from the g1049 example) are correct. In addition, the second example is useful in its illustration of the setting of the 11minute value.

Roger

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Roger, yes I should have said I was referring to MichaelG's link. I agree with the figures in the example in the manual that you referred to, but in the second example, I feel there is a bit of text missing on how to arrive at the 10' graduation before adding the odd minuet to make the 11' graduation. It may confuse those who are trying to learn how to read them, although the 10' graduation is described in the first example.

Regards Nick.

[Roger HeadParticipant @rogerhead16992]

Yes, it could have done with a few more words. But it's always good to exercise the grey cells just a little bit .

Roger

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Nicholas Farr on 02/04/2016 11:20:11:

Hi Roger, yes I should have said I was referring to MichaelG's link.

.

Oh, the shame

Oh, the humiliation

MichaelG.

[BWParticipant @bw]

Hey, Am curious. How accurate are rotary tables in real life – anything is possible in a spreadsheet.

ie if someone sets up an angle of 2 degrees 50 minutes 5 seconds

realistically is it plus minus 5minutes ? plus/minus 5 seconds ? By the time you have walked around a circle of say 127 steps ow far off the starting point are you likely to be.

I've never used one, got a manual one that I made myself didnt come with a manual.

Bill

[Roger HeadParticipant @rogerhead16992]

Turning the worm the required number of times to complete one revolution of the table will always bring you back bang on your starting point, the main gear has exactly 360.000deg. It's not like an Escher stairwell where you could vanish into another dimension before winding up back where you started. However, along the way, their are various errors that occur and can interact (e.g. cyclic errors in the worm itself, and the mating gear) to make an absolute determination of the exact angular position after some number of turns of the wheel an unlikely proposition. Offhand, I don't think you're likely to see accuracy or repeatability specs for any of the RTs at our level. They will, of course, quote the setting resolution (the markings on the wheel and collar, and any vernier graduations), but you can decide on the likely accuracy yourself.

Expensive RTs, like those from Haas or Fanuc for example, quote numbers between 10 and 20 arc-seconds for accuracy and repeatability.

Digital scale implementations that would provide resolutions of 1 Arc-second or better would be relatively straightforward, although some degree of linearization might be be required if the ultimate accuracy was required – and you had won the lottery!

[Quote]

… got a manual one that I made myself didnt come with a manual.

[/Quote]

Never bothers the Chinese, just grab someone else's, a bit of cut'n'paste, never mind if it isn't exactly accurate, or doesn't quite make sense, and Bob's your relative.

Roger

Edited By Roger Head on 03/04/2016 08:48:41

Edited By Roger Head on 03/04/2016 08:49:25

[Michael GilliganParticipant @michaelgilligan61133]

Bill,

That's a very pertinent question; and Roger has given an excellent answer.

… anything better than +/- 20 seconds 'uncertainty' is heading into Metrology Lab. rather than Engineering Workshop territory.

I would just add a couple of points:

1. Centration [concentricity] of WormWheels becomes quite significant [Astronomers become well aware of Periodic Errors]
2. It is worth noting how small an angle 'one second of arc' really is.

As a sanity-check; make a little target with a 1mm wide line on it [when I did this, I just filled-in alternate spaces on a section fom an IKEA paper tape-measure] … Then view that target at a distance of 206.265 Meters. … At that distance, 1 second of arc is subtended by 1mm.

MichaelG.

.

Edit: Due deference to to Roger … I realise that you had mentioned cyclic errors.

 

Edited By Michael Gilligan on 03/04/2016 09:20:03

[BWParticipant @bw]

Thanks for the answers.

People interested in this might enjoy reading George Thomas book where he has a worm turning a spur gear which them turns a second worm gear onto another spur gear which turns the workpiece. See photo here.

http://s657.photobucket.com/user/pherdie/media/VersatileDividingHead2.jpg.html

In this system tiny tiny increments are possible, and again, have always wondered if the plus/minus of cumulative innaccuracies might obliterate the expected precision. ( Maybe the George Thomases of the world simply dont tolerate any inaccuracy anywhere – he seems quite amazing.)

Apologies to OP not sure of etiquette on this – seemed vaguely relevant to the topic and was curious.

Bill

[Nicholas FarrParticipant @nicholasfarr14254]

Posted by Michael Gilligan on 02/04/2016 13:30:05:

Posted by Nicholas Farr on 02/04/2016 11:20:11:

Hi Roger, yes I should have said I was referring to MichaelG's link.

.

Oh, the shame

Oh, the humiliation

MichaelG.

Hi MichaelG, no need for shame or humiliation, I only checked it out to see if I could remember how to read them myself, as I don't know of any occasion that I've used one in this way.

Regards Nick.

[Michael GilliganParticipant @michaelgilligan61133]

Nick,

Very kind of you … But I quoted a reference that contained a significant error .

… It's sackcloth and ashes for me. !!

MichaelG.

[Author]

Posts