Ball Bearing Speed Reducer

A ball bearing speed reducer works like a sun and planet gear box crossed with a normal ball race.

Used to operate a focuser or radio tuner the outer race is fixed. As I understand it, a knob attached to the ball carrier (and shaft) gives high speed and one attached to the inner race is the slow-speed.

But it's frying my brain trying to figure out how they are actually fixed into place so they can be adjusted easily. Photos of partly dis-assembled ones don't help much.

I can't find a sectional view on google, can anyone help?

Neil

Are you thinking of a the type of speed reducer where a flexible gear has an oval shaped ball race inside it and an internal gear with two more teeth surrounds it. As the ball race is turned the teeth walk round the outer gear producing a large speed reduction. Search "Harmonic drive" often used on robots. If the input goes into the centre of the ball race then one turn will advance the flexible wave gear by two teeth inside the fixed outer gear the output is taken from the flexible gear which is cup shaped with the gear teeth round the rim of the cup.the bottom of the cup is the output flange.

Mike

Edited By Mike Poole on 24/12/2017 15:05:24

Edited By Mike Poole on 24/12/2017 15:08:22

Edited By Mike Poole on 24/12/2017 15:09:08

**LINK**

and

http://bbs.astron.ac.cn/thread-54988-1-3.html

May help.

Edited By Bizibilder on 24/12/2017 14:51:36

I recall diagrams and a full explanation of the workings of such devices being published in Eureka! magazine, probably early 1990s. Might still be in the attic so if you get really really desperate..... Perhaps it could be tracked down via the fraternity of magazine editors.

Not the geared type mentioned by Mike.  Pure ball bearing construction.

Back in those days Eureka! was a controlled circulation professional audience magazine devoted to novel engineering items and the implementation thereof. For some reason it was decided that I met the recipient criteria from around 1980 to 1995. Don't recall if I bought them home after reading rather than binning. In those days Photonics Spectra was much more relevant but some of the stuff in Eureka! was pretty darn cool.

Clive.

Edited By Clive Foster on 24/12/2017 14:54:31

Looking at that thread, the reduction ratio is given by the ratio of the radius of the central shaft (where it contacts the balls) to the diameter of the balls. Sound right?

So for a high reduction, you need big balls and a small shaft. Oh dear....

Murray

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I've got one of the 'tuner' ones tucked away somewhere, Neil

It might be a few days before I can locate it ...

If I recall correctly, the knobs are concentric, and the device fixes in place like a normal 'pot' on a panel.

MichaelG.

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Edit: just found this, which may help

http://antiqueradios.com/forums/viewtopic.php?f=5&t=293779

Edited By Michael Gilligan on 24/12/2017 17:37:50

No

That's one that works like a daisy wheel rducer and is unlikely to be smooth enough & backlash free for a focuser

Indeed, I probably have one of those in my dad'd loft, which isn't much help...

7mm bearings and a 2mm shaft are suggested to give approximately 10:1, exact ratio is unimportant

Michael,

The focus control on a Vickers Patholette microscope uses what I was taught to call an 'epicyclic ball drive'.

Best regards,

Swarf, Mostly!

Thanks Bizibilder, I've been pointed at that chinese thread by someone on SGL who has made one, together with a description by someone else who has made one I think I follow it now.

Some tight tolerances to work to!

Hmm I have 14mm and 7mm ball bearings

I think a larger version would be better and more in proportion with the GSO one in the link.

I assume the outer race in the fixed bracket is tapered to allow adjustment, pull the brass rotor into the taper and it moves all four of balls, rotor, inner and outer surfaces into contact.

Neil.

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Mmm ... interesting ^^^

I have both a Metalette and a Patholux, which are variations on the theme; but I wasn't aware of their use of an 'epicyclic ball drive'.

MichaelG.

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For the unitiated: here's some info about the Patholette:

http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artdec01/vickers.html

Edited By Michael Gilligan on 24/12/2017 20:12:37

I see you were looking at a completely different animal to what I thought, I can see that should be very smooth and free of backlash but of very minimal power transmission which is fine in the application. The Harmonic drive is commonly used in robotics for its large speed reduction and near zero backlash. Not being familiar with telescope terminology I imagined it was for actually turning the scope bodily rather than a control function. Sounds like an interesting project if you are going to make such a device.

Mike

Hello Neil.

Would what you are looking for be a simplified version of the Cop (Kop?) variator variable speed drive as fitted to the Colchester Chipmaster Lathe? ie, steel balls traversing the face of a steel disc plate as a friction drive. A google search I think will bring up pictures / drawings

Wishing all a happy Christmas

Anna

The Kopp ball variator is quite different. For one thing it allows the drive ratio to be varied either side of unity, typically by a ratio of 3.

The system being discussed above has a fixed (reduction) ratio. The outer race (ring) is fixed and the balls are driven by the central shaft. The (fixed reduction) ratio is determined by the relative diameters of the balls and the drive shaft and could theoretically be anywhere between 0.5 and approaching zero (if you had massive balls and a small diameter shaft).

Murray

Apologies to Neil for going off-topic.

Michael,

I've referred to that Paul James description myself in the past but I only noticed this morning what he says about the fine focus. What I wrote about the 'epicyclic ball drive' contradicts his description so I withdraw my assertion pending a check.

I bought a Patholette but the seller didn't immobilise the stage when packing the instrument for shipping. So it arrived with the focus lever in two parts, broken at the ball-headed screw pivot hole! That was a CTS Patholette - after the Vickers merger/takeover, the arm was 'beefed-up' in that area. I stripped the damaged instrument for spares and should still have the focus mechanism somewhere. I'll dig it out and check it.

Maybe in 2018 the focus block of my Ortholux (with the solidified grease) will get to the top of the to-do list!!

Best regards,

Swarf, Mostly!

I'v got a number of them on radio gear that L used to build, and one that I made myself. The inner shaft has a taper on the area where the balls run, there is a quite strong spring to tension the shaft in the hole to force the balls between the shaft and the speed reduced outer, I'll try and find it so I can give a better description. It could be scaled up quite a bit.

Ian S C

I'm going to try 3D printing a mockup with 14mm balls.

Neil

The Bon Scott version?

The radio tuning drives are originally from Jackson Bros., and still available (in the new year) and manufactured by Mainline Electronics in Leicestershire

https://www.ebay.co.uk/itm/Jackson-Bros-4511DA-1-4-Ball-drive-new-stock-H3-/292084783788

https://www.mainline-group.com/collections/reduction-drives-classic-6-1

https://www.royalsignals.org.uk/jackson_bros_caps/index.htm shows dimensional drawings.

David Clarke.