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Soba rotary table

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John Pace15/03/2019 10:46:47
122 forum posts
121 photos

Posted by Neil Wyatt 14/03/2019 22:09:51

Good idea John, a bargain basement (<£5) angle grinder 36-tooth
gear might be just the thing for a small rotary table.

Hi Neil,

Not so sure how that a mating worm could be made to work
satisfactory with one of these gears.
The principle of these spiroid gears is the form of the hob is
the same as the worm that is used to drive it.

The photo here shows the gear being cut ,this gear was made
using prototyping wax as it was just an experimental tryout.
A proper gear would need a hob to be made similar to the
style in Heartland gears www.itwheartland.com.As can be seen
the thread form is asymmetric.

The position of the centre distance of the hob needs to be
noted down as the worm has to be placed in this exact position
for this to work.
At 60 tooth and 1 module a spur gear would be 62 mm od ,
this spiral gear also 60 tooth is 84 mm od.
As worm and wheel rotary tables have the worm outside the radius
of the wheel the case size is larger than it needs to be to accommodate
this.
As the placement of the spiroid worm is within the radius of the gear
a larger gear could fit within the same size casing of a rotary table.
As far as accuracy is concerned i can't see that it would be any
different to any other generated gear form.
John
60 tooth 1mod.jpg

JasonB15/03/2019 11:07:05
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14864 forum posts
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I still don't see that giving any more contact than the typical rotary table would and low helix gearwheel ( they are not curved face wormwheels) happy to be proven wrong. I think the reason the rotary tables don't use the curved face of a typical worm wheel is that you would not be able to swing the worm out of mesh as easily as you can using the eccentric mount for the handwheel spindle.

If you look at that spiroid video the pinion is tapered and has a 3 or 4 starts other wise it would not mesh with teh teeth of the gearwheel

Michael Gilligan15/03/2019 11:16:01
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12689 forum posts
551 photos
Posted by JasonB on 15/03/2019 11:07:05:

If you look at that spiroid video the pinion is tapered and has a 3 or 4 starts other wise it would not mesh with teh teeth of the gearwheel

.

I don't have the drawing skills, or the 3D CAD package, to check it ... but I suspect that it would be possible to contrive a single-start worm that would drive one of these wheels. [good enough for Jazz, as Mike said earlier]

MichaelG.

JasonB15/03/2019 11:26:02
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14864 forum posts
1492 photos

I'm sure something could be made to drive one of those wheels Michael but they were suggested as a way of avoiding stripped gears on conventional rotary tables by offering "full contact" so unless you have a full contact worm you have not gained anything over the original gears and with forever by jazzy.

Andrew Johnston15/03/2019 11:33:35
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4448 forum posts
516 photos
Posted by John Pace on 15/03/2019 10:46:47:

As can be seen the thread form is asymmetric.

That's interesting; some of the internet pictures I looked at showed a highly asymmetric worm, also like a butress thread. Like a butress thread that would be good for power transmission in one direction; not so sure about accurate indexing in both directions?

Nevertheless it's a very impressive demo of hobbing.

Andrew

Michael Gilligan15/03/2019 11:36:26
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12689 forum posts
551 photos

[ Jason ]

But at least they are a dirt cheap and easily replaced 'consumable'

... unlike the 47 tooth specials

MichaelG.

Edited By Michael Gilligan on 15/03/2019 11:37:53

Michael Gilligan15/03/2019 14:35:24
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12689 forum posts
551 photos
Posted by JasonB on 15/03/2019 11:07:05:

I think the reason the rotary tables don't use the curved face of a typical worm wheel is that you would not be able to swing the worm out of mesh as easily as you can using the eccentric mount for the handwheel spindle.

.

Just reading back over this thread, and realised that I had missed that comment, Jason

For what it's worth: My BCA has both a throated worm wheel and a worm that can be readily swung our of mesh.

... Might have something to do with it using 180 teeth on the periphery of the table.

MichaelG.

.

Edit: These photos will save me the need to go out in the cold to photograph mine:

http://www.myford-lathes.com/milling_acc5.html

Edited By Michael Gilligan on 15/03/2019 14:37:32

JasonB15/03/2019 15:22:18
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14864 forum posts
1492 photos

Ah but it looks like you swing the other way!

I assume two bolts are undone and it pivots horizontally about that small pin at the front.

The eccentric action found on the Soba, Vertex, ARC etc move the worm upwards and out which would not be possible if the wheel wrapped around the worm as per BCA.

Andrew Johnston15/03/2019 15:58:17
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4448 forum posts
516 photos

My Elliott dividing head definitely uses a single enveloping worm wheel, and the worm disconnect is by way of an eccentric shaft. In contrast my "no name" rotary table uses a disconnect where the worm shaft has a single pivot. While it's a long time since I stripped down the rotary table I pretty sure it also uses a single enveloping worm wheel.

A worm and helical gear has point contact; a worm and single enveloping worm wheel has line contact. So less wear and tooth stress when reacting cutting loads.

Andrew

Michael Gilligan15/03/2019 16:01:58
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12689 forum posts
551 photos
Posted by JasonB on 15/03/2019 15:22:18:

Ah but it looks like you swing the other way!

.

surprise ... to whom ?

angelblush

Edited By Michael Gilligan on 15/03/2019 16:18:01

Lathejack15/03/2019 20:20:47
224 forum posts
278 photos

I bought this 150mm Vertex Rotary Table new just over 15 years ago, the TOS chuck with mounting plate that I made is fitted most of the time.

This older version of the Vertex table has a hardened removable sleeve in the centre that is bored 2MT. The table also rotates in a radial needle roller bearing. The original factory fitted bearing shown was a German made item. It also has a needle roller thrust bearing under the base casting.

The radial needle roller bearing had to be replaced a few years after purchase because the factory applied grease had dried solid and jammed up the bearing. The outer race was forced to rotate in the housing of the base casting, it still ran smoothly and was only discovered when the table was stripped for a clean and lube up.

image.jpg.

................. My Rotary Table hand wheel tightens or binds a little through part of every revolution. This was found to be caused by the graduated collars front face being machined slightly out of square with its bore, the mounting bracket also has the same fault. If the two faces are very close or touching it causes the intermittent binding, which feels like a more serious internal fault with the meshing gears. Back the collar off a little and the table is superbly smooth. It may be worth checking this first if you have a table that binds in a similar manner.

Other than those two snags it is very well made and well with the £130-£150 it cost back then.

image.jpg

Edited By Lathejack on 15/03/2019 20:23:00

Chris Trice15/03/2019 21:50:12
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1332 forum posts
9 photos

That's the one I've got and your experience pretty much matches mine except in my case there was no hardened grease problem. It's a nice piece of kit well worth the money.

Neil Wyatt16/03/2019 08:47:44
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15581 forum posts
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It's also possible to use a curved worm with an enveloping wheel for maximum contact.

geoff walker 116/03/2019 11:47:42
274 forum posts
116 photos

Hi Neil

My table has the cylinderical worm enveloping gear, very nicely made, all 47 teeth!!!!

Geoff

Pero17/03/2019 00:25:46
74 forum posts

A little follow up on the 47 tooth issue.

I contacted RDG who responded quickly saying that they are contacting their supplier. I am waiting for the next response - I am assuming the weekend may have got in the way.

A slightly crude approach to the measurement of the worm height would suggest it is 18.5 mm plus or minus a tad ( one tad being equal to or less than 0.5 mm ).

This would mean that a NEMA14 would fit comfortably but given that loading would be light (mill with a high speed spindle driving small mills and drills ) I think I might opt in the first instance for a smaller NEMA11 to reduce weight.

Have yet to get into the workshop ( it's a fight ) to dismantle it and see whether it is worth the effort of motorizing it and to consider the motor mounting options.

After twiddling the little handle almost countless ( pun intended ) times to confirm that I too had 47 teeth I quickly became convinced that motorization is a necessity to prevent insanity, whether it is on this or an alternative small table!

Pero

Michael Gilligan17/03/2019 08:13:57
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12689 forum posts
551 photos

Thanks for the update, Pero yes

I look forward to seeing some photos of its innards.

MichaelG.

Ron Laden18/03/2019 15:27:01
933 forum posts
136 photos

Well it will be interesting to see how my Soba measures up as I have just ordered one, I have the little cheapie table but a better RT was on my future shopping list. I think a 6 inch version may be a bit big for my mill (SX2P) and was thinking that a 5 inch would be ideal and then found that Soba do a 5 inch.

I have gone for a set which has the RT, a dividing set, a tailstock and a 4 jaw chuck with mounting plate and its a very good price so I have brought it forward a bit.

Ron

Paul Kemp18/03/2019 16:10:59
208 forum posts
9 photos

Ron,

As I mentioned I think when you were looking for the first RT try and pick one where the locking / clamping arrangement pulls the table down on the base rather than with a screw that goes in on the side as if there is any play it will jack the table over when you lock it. Good move to get the tailstock too, always useful and a four jaw is a lot more versatile than a three jaw, you can overcome any inaccuracies in location of chuck to table by clocking the work in a four jaw, with a three jaw you are stuck with what you have and it doesn't take long to clock something true in a four jaw once you have had a little practice! Also a four jaw gives a better grip on round stock that a three jaw and allows irregular shaped work. So out of choice the 4 jaw is a lot more versatile if on a budget. You may well find though the standard plate set for the divisions you still don't have the numbers you need but worry not, you can make your own as long as you are not fussed about microns of a division!

Paul.

Pero20/03/2019 00:14:49
74 forum posts

An update on the RDG 2 3/4" rotary table.

I have received an email from RDG advising that their supplier would be sending me a ( checked [their advice] ) new table direct. A very good outcome.

Many thanks to Geoff Walker for pointing out the problem as mine was still in the original packaging and it may have been some time before I discovered the problem for myself.

Notwithstanding, I think I will still potter along with the motorising option as that tiny handle is a pain ( and I tend to lose count ).

I still haven't got to the dismantling yet but will attempt to send photos in due course.

Pero

geoff walker 120/03/2019 11:24:04
274 forum posts
116 photos

HI Pero,

New table, that's good news. Glad I was of help.

I've had mine nearly a year and have used it a lot.

It was only in the last month that I realised the main gear had 47 teeth.

If you remove the base it reveals the worm and gear arrangement and after several counts I finally accepted 47!!!!.

I'm looking to buy another larger one 4-5" diameter but this time will take advice first.

Geoff

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