Circular Division – and you thought you knew it all!

[Andre ROUSSEAUParticipant @andrerousseau66124]

Just when you thought every man and his dog had fully traversed the wide expansive field of circular division and indexing a whole new contrivance comes hurtling out of the bowels of obscurity!

Enjoy!

[Andre ROUSSEAU]

On 14 January 2026 at 02:54 Andre ROUSSEAU Said:

…a whole new contrivance comes hurtling out of the bowels of obscurity!

The Newbould indexer is well-known. Its inventor frequented the Practical Machinist forum before he passed, and related its story there. Its patent is available. It has also been discussed on YT by Adam the machinist. 3D printed versions have been discussed.

New to you perhaps if your only source of information is an algorithm feeding you videos.

[Michael GilliganParticipant @michaelgilligan61133]

The genius of the invention is in no way diminished by this witty [dare I say engaging ?] video … this is education.

MichaelG.

[Andre ROUSSEAUParticipant @andrerousseau66124]

It’s also surprising that Newbold’s innovation is comparatively, a recent one and that no-one else (it seems!) in the previous century-and-a-half of modern industrialisation seems to have tumbled on to it. I’m keeping my own unique division techniques to myself in the meantime.

[Andre ROUSSEAUParticipant @andrerousseau66124]

Instead of flaunting your ego and merely re-gurgitating the contents of the video to make yourself look clever why don’t you instead ‘click-off’ somewhere else since you’re obviously so bored with the subject and let the majority of others who haven’t heard of it gain some inspiration and knowledge, unfettered by your uncharitable caustic commentary! Have a good day….

[John HaineParticipant @johnhaine32865]

https://patents.google.com/patent/US3846912A/en

Invented before 1972, can’t be that obscure as there is one in the Smithsonian.

[noel shelleyParticipant @noelshelley55608]

Now that’s what I call VERY CLEVER !    Noel.

[Nigel Graham 2Participant @nigelgraham2]

I am only surprised the principle was not realised much longer ago, perhaps even by someone like Charles Babbage.

At simplest the addition / subtraction is not unlike stacking feeler-gauges or gauge blocks, but this device seems a logical development of the Vernier principle. However, I am not a mathematician so could be wrong!

Perhaps nearer is the idea of concentric screw-threads of different pitches to give very fine axial adjustment, but I forget where I saw this described, and for what application.

[John HaineParticipant @johnhaine32865]

Differential screw. I have seen it used for various fine adjustments on microscopes.

[John HaineParticipant @johnhaine32865]

Like most inventions it’s a logical development once you see it but a creative leap by someone  in the first place!

[DC31k]

On DC31k Said:

On 14 January 2026 at 02:54 Andre ROUSSEAU Said:

…a whole new contrivance comes hurtling out of the bowels of obscurity!

The Newbould indexer is well-known. Its inventor frequented the Practical Machinist forum before he passed, and related its story there. Its patent is available. It has also been discussed on YT by Adam the machinist. 3D printed versions have been discussed.

New to you perhaps if your only source of information is an algorithm feeding you videos.

I enjoyed reading the story on PM very much. He ran through his thought and reasoning processes and then after building the first one also recounted his tale of taking it to show Moore & Wright who – before they actually saw it – said that such direct indexing was “not possible”.

[BazyleParticipant @bazyle]

If I have understood this correctly one of the special indexes is at 2deg10min or 2.16666667 degrees equivalent to a gear with 166.15385 teeth and the other is at 2deg30sec or 2.008333333 degrees  equivalent to a gear of 179.2531 teeth. (not entirely certain about the second one)

So: does your favourite CAD program gear generator accept this sufficiently to produce STLs for 3D printing the required part?

I must remind myself how to do the dividing head calculations to do it on a differential indexing head.

[JasonBModerator @jasonb]

Alibre will take minutes and seconds as imput then take care of whatever they are in decimals. I could set it to show multiple decimal places if I wanted.

Or as they don’t cover a full 360deg you could just enter the total number of divisions and the total angle they occupy and then let the CAD divide that up.

 

[Pete RimmerParticipant @peterimmer30576]

I kinda mis-remembered the details but in my defense it was nearly 18 years ago. If you want to read the first-hand account from Newbould himself then it’s here:

Newbould indexer story

 

[Michael GilliganParticipant @michaelgilligan61133]

Thanks for the link, Pete

MichaelG.

[John HaineParticipant @johnhaine32865]

There is a motor-driven version that appears to have only degree divisions on eBay at the moment at nearly $2500!  One active offer apparently.  So obviously in demand.

[Phil PParticipant @philp]

There is another complete one on ebay USA which is a bit cheaper.
Item 195848057504

Phil P

[John HaineParticipant @johnhaine32865]

fewer bits though.

An interesting challenge: how could one do this with a combination of mechanics and stepper motors, given that microstepping is really not very accurate?

[BazyleParticipant @bazyle]

The Kearney and Trecker model K dividing head with astronomical divider attachment is set in degrees, minutes and seconds. The accuracy though is dependent on the worm wheel as would a stepper motor based design. Taking the currently popular method of using a rotary table 90:1 wormwheel rather than the 40:1 of a dividing head, then with 8 microsteps each step is 9 seconds. Simple halfstepping which is inherently more accurate than microstepping gives a ‘useful’ 36 seconds, of dubious precision.
However the use of a stepper implies a computer and with that comes the potential of calibration tables for every part – wormwheel, stepper, microsteps that could be used to hugely improve the cheaper components. I wonder who actually needs such accuracy.

[Bazyle]

On Bazyle Said:

……. I wonder who actually needs such accuracy.

Well, presumably the people who buy the Newbould Divider?

[Nigel Graham 2Participant @nigelgraham2]

I suppose accuracy – or precision, I can never remember which is which of these non-synonyms – to that level would be in the realms of aeronautical engineering, scientific instrument making, and such fields.

I don’t know the fine-ness of astronomical telescope steering, but angular measurements in that science must be critical to very fine limits.

[John HaineParticipant @johnhaine32865]

Standard astronomical length unit is the parsec which is the distance that subtends an angle of 1 arcsecond at 1 au where 1 au is defined to be 149,597,870,700 m, originally the mean earth-sun distance.  1 parsec is about 3.26 light-years.  So measuring to 1 arcsecond is a requirement.  (All this from Wikipedia.)

Interestingly reading Newbould’s posts the resolution of his indexer is 1 second but absolute accuracy not so good.

[Bazyle]

On Bazyle Said:

[…]  Simple halfstepping which is inherently more accurate than microstepping gives a ‘useful’ 36 seconds, of dubious precision.
[…]

It is worth noting that the typical stated tolerance for full 1.8° steps is ±5% per step (non-cumulative).

MichaelG.

[John HaineParticipant @johnhaine32865]

Well it seems someone at least has solved the problem.

Mike Everman who is the company Principle is a keen horologist and I believe may have posted here?

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