How to measure minutes and seconds
|martyn nutland||17/01/2021 14:58:55|
|124 forum posts|
I've got a Vertex rotary table. I think it's a V4 model. I've only ever used it to make incremental cuts (e.g. bolt circles) which is, admittedly, very easy using the main degree scale of the table and has been totally successful.
Apart from the main 360° scale on the table I have 120 divisions behind the hand wheel (two hours?) and then six divisions on the inner scale (tenths of one minute?). So...wind on 0-19° on the main scale...then what...?
Also, could I ask, what is the pin/lever about an inch long that screws into the second scale ring for? All I can see that moving it ever does is reverse the direction of the table when you turn the handle (if you hold said lever it over!)
Sorry to be so basic. But guidance would be much appreciated and, as always, thanks in advance.
Best wishes and keep safe.
|old mart||17/01/2021 15:14:15|
|2659 forum posts|
Seconds of arc may be beyond the capabilities of your table, my 6" Soba only goes to the nearest minute.
|Roger Woollett||17/01/2021 15:32:25|
|120 forum posts|
I think you will find the table has a 90:1 worm so each turn of the handle moves the table 4 degrees. The hand wheel is marked 0,1,2,3 to give you the intervening degrees. Between the degree marks are thirty divisions with the middle marked 30. Each of these divisions is two minutes. You might be able to get to the nearest minute but I doubt you could accurately set to seconds.
|not done it yet||17/01/2021 15:44:31|
|5581 forum posts|
On a 100mm circumference, one minute of angle will be a movement, at the circumference, of 0.015mm, so 12 minutes would be 0.003mm - better than most of us measure to!
19894 forum posts
As supplied the rotary tables handwheel is going to be too small for being able to read off those small amounts. So assuming it's a 90:1 ratio draw up and print of a disc say 150mm diameter with 240 divisions which will each be 1 degree and stick that onto the R/T's handwheel. Then draw up a vernier scale with 60 marks over the distance of 59 of the marks on the disc and that will then let you measure to 1 minute and possible guestimate 20seconds. A larger diameter disc will reduce errors.
Edited By JasonB on 17/01/2021 16:09:14
|384 forum posts|
There is a manual describing the parts here:
As that is an Australian version, the table might go in the opposite direction when you rotate the handle.
As others have said, it has a 90:1 worm ratio. Hence, one turn of the 120-division wheel moves it 4 degrees.
At this point, your description and the manual linked to diverge as it claims the micro collar resolves to 1 minute, which implies 240 divisions.
In any case, if your inner scale has six divisions, it will not be tenths of anything, but sixths, more specifically sixths of whatever one division of the outer scale represents.
Mr not done it yet's post contains some serious typos, so should be read with caution. To correct it, substitute 'diameter' for the first mention of 'circumference' and '12 seconds' for '12 minutes'.
5148 forum posts
Is this for gear cutting or the like? Can you get a set of indexing plates and the indexing plunger handle to fit your table for that? They seem to be cheaply available for a lot of the Chinese tables these days but no idea about your Vertex. You then work off the simple number of teeth on the gear rather than minutes and seconds.
Edited By Hopper on 17/01/2021 16:27:21
Edited By Hopper on 17/01/2021 16:27:50
|Howard Lewis||17/01/2021 16:28:23|
|4397 forum posts|
Is your table a HV4 or RT4?
What does the Manual say about these things?
Not much if it is like the one for my HV6! Seems more concerned with fitting and using the Division Plates.
The following comments are based on my knowledge of the HV6, and the assumption that your 4" table is a scaled down version. So it should be a 90:1 ratio. (90 turns of the handwheel for one complete turn of the table ).
So one turn of the Handwheel will rotate the Table by 4 degrees.
I am too idle to go out into the workshop to get out the HV6 and check, so am relying on memory! And it is a LONG time since I partially stripped one to adjust.
The units on the main scale, on the Rotating part of the Table are Degrees, the graduations on the Handwheel and the Vernier allow you to work to fractions of a Degree, Minutes of a Degree, and then,hopefully, to 1/60 of that, namely Seconds of a Degree, AT THE Table...
Most probably, the divisions on the Handwheel will be Degrees, and the divisions on the other scale will be a vernier, allowing you to work to Minutes of a Degree.
If you check, you will find that the six divisions on the vernier scale do not correspond exactly to those on the handwheel. Probably coinciding at the zero and fifth divisions on the handwheel. This is deliberate, to produce the vernier effect, so that moving the handwheel so the coincidence changes from the zero to the first graduation on the vernier needs only a tiny rotation of the handwheel.
If there are 120 divisions on the Handwheel, each graduation probably represents 3 degrees ON THE HANDWHEEL, or 0.0333333 degrees, or 2 minutes, OF THE TABLE.
Using the vernier scale, it is possible to rotate the Handwheel by a lesser amount and so obtain an ever smaller incremental movement of the table.
At an unchecked guess, (Which someone is likely to correct ) this movement of one division on the vernier scale will represent 3/6 degrees or 30 minutes of Handwheel rotation producing 0.33333 Minutes or 20 Seconds of TABLE rotation. Hence my being pessimistic over being able to obtain your final 12 seconds
You are looking for a HANDWHEEL rotation of 4.770833 turns to obtain 19.083333 Degrees of the table. This is dividing a circle into almost 19 divisions, but not quite, (18.864629 divisions ).
BUT, if it needs to be said, the backlash MUST be taken out., so I would recommend setting the table locks to drag slightly, and ALWAYS to rotate the handwheel in the same direction.
I would be surprised if the lever to which you refer reverses the direction of rotation. There may well be such a provision, but I have never heard of it. It would be more like;y to allow the worm to be moved in and out bof mesh with the wormwheel.
.This achieved by rotating the eccentric sleeve which carries the worm shaft. The position of this sleeve is locked by a small handle in the base of the table, just by the handwheel, behind the vernier scale. .
If the "Second scale ring" is on the Hnadwheel, this may be to allow the handwheel to be moved relative to the wormshaft so that the scale can be zeroed against the Vernier scale, before commencing rotation of the table
All these assume that the worm and wheel ARE accurate. (There have been posts on here of a table supposedly having a 48:1 ratio being found to have a 47 tooth wormwheel! )
You quote figures requiring a high degree of accuracy, (Possibly higher than the table can deliver ) so check everything!
Edited By Howard Lewis on 17/01/2021 16:35:17
6857 forum posts
Sounds like mine, which is as described by Roger.
The pin, shown disengaged, turns the inner scale to engage the worm to drive the table. Mine doesn't do reverse. The T handled nut behind locks the worm in or out of position. Undo it to move the inner scale and re-lock at each end.
Before turning the inner-scale with the pin also make sure the table's locking clamps are undone. Being relatively crudely made, the worm doesn't always mesh properly and it helps to turn the hand-wheel and pin together in the same direction. On my table the pin ends up on the left side with the inner-scale central on top.
As Roger says, each turn of the outer scale is 4°, and it is graduated in steps of 2 minutes. The inner-scale is a vernier going down to a third of a minute (20 seconds). Actually, mine isn't that trustworthy - I wouldn't claim better than half a minute, and that's optimistic! Assuming I've read it right, the dial above is set to about 13½ minutes past 0°.
Having zeroed the table, 19°3'12" is 4 full turns of the handwheel to get 16°, plus ¾ turn to get to 19°, plus 3 and a smidge small graduations past the centre line on the inner scale.
I guess Martin isn't making a gear because 360 / 19°3'12" isn't a whole number, but say he was after a 19 toothed gear. Keeping track of multiples of 18° 56' 51" is such a right royal pain that a dividing wheel attachment is available to help.
Although the wheels help a lot, I won't fib by saying they're easy to use. Lots of us have motorised our tables and added a microcontroller to do the sums and keep count.
|Howard Lewis||17/01/2021 17:06:55|
|4397 forum posts|
The pictures show everything so much more clearly.
If your objective is to cut a 19T gear, or to drill 19 equally spaced holes, you need the Division Plate set, and a Tailstock..
If you fit the A plate, and work on the 19 hole circle, you will need to rotate the Handwheel by 4 turns and 14 holes on the plate for each tooth. There should be a chart supplied with the Table.
The chart for my early HV6 contained errors, and had to be recalculated! It is available on here, if you search for HV6. With a 90:1 ratio, the figures should be the same for your HV4
For gear cutting, I turn up the blank in the lathe, with a centre drilling in the outer end before transferring the chuck and workpiece, undisturbed, to the Rotary Table. The Tailstock for the Rotary table is used to support the outer end of the workpiece during cutting.
It is taken as read that the R T is set square across the table of the mill, (unless you are cutting a helical gear ) and that the Tailstock is correctly aligned with the R T in both horizontal and vertical planes.
Gearcutting is pretty hard labour for the machine, since the cut is taken to the full depth shown on the cutter, in one pass, with a very fine feed.
The proportions of the workpiece need to be such that the cutter does not cut the tailstock, nor hit the jaws of the chuck .
A 1 Mod gear with 19T will be 21 mm diameter. A 20 DP gear with 19T will be 1.05 inches diameter.
If you expect to cut gears again, buy Ivan Law's Book, "Gears and Gear Cutting", No 17 in the Workshop Practice Series. You will find it a great help.
19894 forum posts
The photos are not of the OPs rotary table, the angle he wants to cut will not divide into 360deg
5148 forum posts
Might be time to use a sine bar instead of a rotary table then if it is a one-off angle to be machined. Get it dead nuts precision that way.
But without knowing what the job is we can only guess.
|Nicholas Farr||17/01/2021 17:17:33|
2616 forum posts
Hi, my 6" Vertex is the same as SOD's and like he says, has a resolution of 20 seconds at best, using the vernier scale, which is the 60-0-60 scale.
Which is reading 1 degree 25 minuets and 20 seconds, with the table turning clockwise.
Edited By Nicholas Farr on 17/01/2021 17:22:32
|Howard Lewis||17/01/2021 18:13:31|
|4397 forum posts|
Martin, please see below mt response to Jason,
Several of us pointed out that the 19 degrees, 3 minutes and 12 seconds was not an exact 19 divisions (18.86 ) and someone suggested that maybe the requirement was for 19 divisions. Hence my comments re the need for Division Plates.
I thought, quite rightly as you say, that the pictures were of someone else's R T, and implied that it they were of a 4" (which looks very like my HV6 ).
Judged by the Vertex Operation and Service Manual, showing the same exploded views for their tables, with the discrimination on part number being purely by the table for which the part is intended, the construction seems to be same for 6, 8, 10, 12 and 14 inch models, with just dimensional differences between the components., so I assumed that a HV4 would be similar.
The thing which intrigues me, and probably others, is the 19 degrees 3 minutes and 12 seconds.
Is this angle the result of a calculation based on measured dimensions? Or is it mandated by some other factor? What is the context of this angle needing to be so precise?
19894 forum posts
Another option if you have a DRO is to make a direct indexing ring that can fit to the face of the rotary table with a series of holes at your required angle for whatever total arc you need and then rig up a pin to index the holes with.
19894 forum posts
Howard a look back at one of Martyn's recent posts may shed some light onto the requirements, still not sure why he wants to rotate the R/T by this amount
Could ther ebe a link as you mention 18.947deg which is just about 0,3', 12" short of 19deg
Edited By JasonB on 17/01/2021 18:46:44
5778 forum posts
Just raw in some extra lines on the vernier and you have 10 seconds - only 2 seconds off. As mentioned above the wormwheel won't be any more accurate.
|Howard Lewis||17/01/2021 19:22:27|
|4397 forum posts|
If it is for a Simms Vernier coupling, why not go for 20 Divisions on one side and 19 on the other.
But I think that we have trodden this path in the Simms Coupling thread.
|Michael Gilligan||17/01/2021 21:47:38|
17279 forum posts
Here’s a reality check
This dividing head is [just] capable of resolving one second of arc:
< click should provide a larger image >
Don’t get too excited about the prices ... I think the catalogue is dated 1964
P.S. __ Here’s something that I posted in 2016 :
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.
Edited By Michael Gilligan on 17/01/2021 22:07:21
|martyn nutland||18/01/2021 12:22:05|
|124 forum posts|
Thank you everyone.
I've sent for the Laws book. It hasn't arrived yet ( Jan 27 estimated ) and that should also help.
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.
I find I can get 19 divisions (as per the originals) on the direct indexing scale of my new dividing head to about a one degree discrepancy over the 360°. Certainly good enough for this purpose. However, I did think I might be able to split that one degree inaccuracy using the minutes/seconds facility on the rotary table. It's probably possible to get a division of 19° 3', but not the seconds, because, as has been pointed out, the device is simply not sufficiently accurate for seconds. Yet, even if you achieved a segment of 19° 3' (or whatever) you would always need to fit (or make!) a dividing plate to the rotary table to proceed and index and cut all the divisions. Thus, you may as well try to do it by indirect indexing on the dividing head, using it's own plates, in the first place!
Thanks again all. Take care.
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