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Soba rotary table

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not done it yet13/03/2019 16:29:15
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Oops, not concentrating!

SillyOldDuffer13/03/2019 17:01:34
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Posted by Oxymoron on 13/03/2019 15:13:16:

Thanks Guys. Pretty much as I assumed, you can manage without the plates but they make it easier. And less error prone. I need all the help I can get!

...

Dividing for all but the simplest divisions soon becomes extremely tedious and it's very easy to lose track.

For example, say you want to cut a gear with 41 teeth in it. Without dividing plates you have to set the scale by eye in 8.78° increments as accurately as you can, 41 times. 82 or 123 times if the teeth are nibbled out or generated.

It's more accurate to count turns and part turns of the handle as dictated by the table's worm ratio. This method is hard to get right without pre-calculation and mechanical help.

Dividing plates come with a printed index table where someone else has done the sums. (Not always correctly -  check for mistakes before cutting metal! ) Looking up my HV6 table with a 90:1 worm ratio, to cut 41 teeth, I need to fit division plate C, then to take two complete turns of the handle plus an index of 8 holes into the 41 hole ring around the C plate. This automates the integer arithmetic and a pair of clock-hands keep track of the next increment and all the others. As mistakes result in the wrong number of teeth or damaged teeth, it's important to minimise them.

Even with help from division plates the process is error prone. The best way to drive a rotary table is with a stepper controller doing the maths and keeping count for you.

I recommend getting a set of division plates if you intend doing any complicated divisons.

Dave

Edited By SillyOldDuffer on 13/03/2019 17:05:22

Oxymoron13/03/2019 17:13:58
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Dave, (SOD) many thanks for taking the time to explain above. Very informative. I've started work on a 1" Minnie and currently turning wheel rims. I figure I'll need a rotary table before long and when it comes to cutting gears which I'd like to try myself then dividing plates could be very useful.

I've learnt a lot from this thread to help make an informed purchase.

Dave

Ian Skeldon 213/03/2019 18:29:17
490 forum posts
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Does anyone here use a Soba roary table without any issues? As already covered it depends on the level of accuracy the user is trying to achieve but it would be interesting to hear from owners of such tooling.

JasonB13/03/2019 19:32:38
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Posted by Ian Skeldon 2 on 13/03/2019 18:29:17:

Does anyone here use a Soba roary table without any issues?

See my post towards the top of the first page.

Ian Skeldon 213/03/2019 20:04:58
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I have seen lots of the things you have made, so in the right hands they're very useable.

Thanks Jason

Hopper14/03/2019 05:33:30
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Posted by Ian Skeldon 2 on 13/03/2019 20:04:58:

I have seen lots of the things you have made, so in the right hands they're very useable.

Thanks Jason

Well the one Jason bought eight years ago was. But see Ketan's posts about declining quality from certain factories/suppliers over the years and you see what a difference time can make. Then see Geoff Walker's experience with a rotary table from another supplier that had 47 turns of the handle instead of the requisite 48. Seems like unless you go for the higher priced items (eg 400 quid) these days you pays your money and you takes your chance.

 

Edited By Hopper on 14/03/2019 05:36:09

Edited By Hopper on 14/03/2019 05:38:33

Pero14/03/2019 06:27:48
117 forum posts

My 4", 6" and 8" rotary tables are all older Vertex so I cannot add comment on the Soba or recent Vertex quality.

However, like Geoff Walker I also purchased the RDG Tools 2 3/4" rotary table, in my case to use with a Proxxon mini mill. The relative scales are just about right - the 8" Vertex is definitely overkill with this machine.

Unopened until today when I read this thread, I opened the plastic bag and lo and behold - 47 turns. Checked it twice counting full turns (47) and once counting half turns (94). Same outcome each time - yes I can still count - hooray.

I checked the RDG website where it is still available and still advertised as 1:48. I have emailed RDG advising of this and asking for a response. Perhaps they will send the missing tooth!

Alternatively does anyone have a recommendation for an itty bitty stepper motor and the necessary program to convert it to a useful bit of kit?

Pero

Michael Gilligan14/03/2019 07:24:43
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Pero,

Your proposed alternative certainly seems the best work-around yes

To keep things compact, I suggest you look at NEMA14 size stepper motors.

for example: https://www.pololu.com/product/1208

https://www.pololu.com/product/1208

MichaelG.

.

P.S. it would be helpful to know the height of the worm axis on that table

Edited By Michael Gilligan on 14/03/2019 07:30:27

JasonB14/03/2019 07:45:41
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Hopper have you got a link to the £400 tables and what sort of spec do they come out at compared to what the OP measured?

Neil Wyatt14/03/2019 08:34:31
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Posted by Michael Gilligan on 13/03/2019 15:13:04:
Posted by Neil Wyatt on 13/03/2019 15:04:22:
 
... to the nearest 0.1 of a degree (ten seconds)

.

dont know

Oopsy! Six minutes...

Edited By Neil Wyatt on 14/03/2019 08:34:48

Neil Wyatt14/03/2019 08:37:24
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Posted by not done it yet on 13/03/2019 16:11:38:
Posted by Michael Gilligan on 13/03/2019 15:13:04:
Posted by Neil Wyatt on 13/03/2019 15:04:22:
... to the nearest 0.1 of a degree (ten seconds)

.

dont know

Nearer 2 thous if 1/10 th, and almost 3 thous if 10 seconds - to the outer edge of a 2" circle?

One might only need a mirror, JB?smiley

Actually, if you work to the nearest 0.1 degree the maximum error is 0.05 degrees, so 1 thou.

In practice I have been known to work to half a division so 0.5 thou.

And yes I had a brian fart...

Neil

Neil Wyatt14/03/2019 08:42:39
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When I made my first rotary table by free hobbing, I got 61 teeth then I used the approach of gashing the blank by indexing it with a change wheel.

I think I still have the duff gear. Pero, I could cut the extra tooth out and send it to you if it's useful...

Neil

Pero14/03/2019 08:44:58
117 forum posts

Thanks Michael

I'm not quite sure how much holding torque I would require and whether I could possibly go down to a NEMA11.

I haven't dismantled it yet - I have to, it feels a bit gritty - so cannot advise on the worm height. I am guessing it will be very low ( probably a bit less than 20 mm ) as the whole table is only 38 mm in height. I suspect with either a NEMA11 or NEMA14 I may have to fit a sub-plate onto the bottom of the table for clearance. That said, the table on the Proxxon MF70 is quite small so the motor might comfortably hang over the edge and its size may then not be a problem.

Further investigations for tomorrow.

Cheers

Pero

PS A check on the Pulolu web site indicates that the centre height on a NEMA14 is 17.5 mm so it should be right on the mark or very close to.

Edited By Pero on 14/03/2019 08:55:45

Pero14/03/2019 08:53:40
117 forum posts

Neil thank you for your kind offer - I may need to take you up on it.

I am waiting for RDG to get back to me. They might possibly have the correct tooth in stock.

After all, I wouldn't want to fit a molar where an incisor should go devil

Pero

Ron Laden14/03/2019 09:22:15
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I have a Warco 100mm rotary table, its all I could afford at the time (£56) and I guess with all cheapies its a bit of pot luck whether you get rubbish or something you can live with for the type of work you give it. When it arrived I clocked it and it wasnt too bad, in fact for the money you could argue quite reasonable.

With some jobs coming up for the electric TE I stripped it down yesterday serviced it and adjusted it to the best I could get it, The method of adjustment is crude so its a balancing act of slackening this/tightening that to get a usable feel from the handle whilst keeping the gear backlash to a minimum.

I spent some time doing this and the best I could get is 0.002" backlash around 270 degrees of the table increasing to 0.003" around the final 90. The edge of the table runs out to 0.005" and a centered 40mm boss 0.0015". For the shaping jobs I have coming along it will be ok and for the money I can hardly complain.

Ron

Hopper14/03/2019 09:35:37
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Posted by JasonB on 14/03/2019 07:45:41:

Hopper have you got a link to the £400 tables and what sort of spec do they come out at compared to what the OP measured?

 

 

The ArcEuro 6" just used as an example, following on from Ketan's posts about the search for reasonable quality suppliers etc. Although I think there were others quoted somewhere in the thread at several thousands of pounds. Compared with the 56 Quid Warco job in the previous post now. For that price, I could live with a few thou slop. And backlash does not worry me at all. Not sure why so many people worry about backlash. As long as direction of movement is uniform, backlash is unimportant. (Maybe I'm just used to using worn out old machines and "backlash compensation" is a natural habit.)

But I don't think I could ever get over the 47 tooth wormgear. The sheer indifference of the manufacturer would bug me every time I used it. I would have to use the table to make a 48-tooth worm gear ring and shrink it on. Could be done I suppose if you turned the handle 46/47th of a turn for each cut, giving you one extra turn at the 48th post for the extra tooth.

Like a micro-drilling attachment I bought recently. For use with .5mm drills and the like. Looks beautiful but the little chuck has so much runout the tip of a drill bit has about .010" runout . So I'll be salvaging a very nice chuck off an old but not worn pistol drill and making my own micro-drilling attachment shank to suit. The old "If you want a job done right..."   Could have saved myself the price of a carton of beer.

 

Edited By Hopper on 14/03/2019 09:51:47

Edited By Hopper on 14/03/2019 10:01:16

John Pace14/03/2019 09:54:00
212 forum posts
194 photos


I just wonder how long rotary tables will be made in the conventional way .
Other threads on rotary tables have highlighted the strength problems
with worm and wheels .
This video shows these spiroid and helicron gears which can be made
with zero backlash.
https://www.youtube.com/watch?v=gRriAf5snqs

A photo here of a test gear hobbed using a 1 module cutter ,the worm would
fit in about the 1 o'clock position and have about 5 teeth in mesh at the same
time.
Johnspiral gear.jpg

Hopper14/03/2019 10:13:00
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Posted by John Pace on 14/03/2019 09:54:00:


I just wonder how long rotary tables will be made in the conventional way .

I reckon stepper motors and control modules will take over from worms and wheels. Must be cheaper to manufacture. Just like the way electronic fuel injection took over from complex mechanical carburettors. Not only delivers a better result but cheaper to manufacture due to almost no moving parts. Ditto points ignition vs electronic. No contest cost wise. Its only a matter of time before it trickles down to hobby workshop indexing heads and tables at reasonable cost. I know there are small CNC dividing heads out there on Aliexpress for about $100 already so its only a matter of time until they take over from worms and gears on rotary tables-- which are 19th century technology still in use!

Andrew Johnston14/03/2019 10:25:15
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I suspect the market for manual rotary tables is relatively small. Industry has gone CNC. A search on professional rotary tables shows a range of drive methods, direct by servo or via worm drives. No stepper motors though. So it seems some high end manufacturers (like Nikken) are still using variations on worm drives. Manufacturers of spiroid gears list a number of benefits such as efficiency, increased power transmission and controllable backlash, but angular accuracy isn't listed. I wonder what the angular accuracy of a spiroid gear is like?

Andrew

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