Strange Miniature Bearing

I am trying to service (fix) a Congreve Clock. The table is suspended on two small - four ball - bearings. The outer race is mounted in the edge of the table, and the inner race comprises tapered steel pins which insert from each side.

Table - the bearing pins are held by a locking screw in the mounts.

The bearings have four balls in a cage, and are 7.75mm OD as near as I can measure in situ, while the open end is 3.50mm ID. The pins are poor shape, and don't seem to be hardened

I will make new pins from silver steel and harden them, but I wonder if anyone can point me in the direction of a source of new bearings - should I need them.

Searches in many suppliers online catalogues have thrown up lots of small bearings, but nothing like this one.

It is possible to buy just bearing balls, and that's likely what you'd need do.

You say your measurement is necessarily approximate, so that odd-looking 7.75mm might be an Imperial diameter, 5/16" (7.94mm) being the closest.

I don't know if the stainless-steel balls sold through "our" trade usually for clack-valves would be suitable, if appropriate bearing-balls prove as rare as fowl dentures.

I doubt if anyone will stock the original type of bearing assembly but you could replace the balls if the guides are not worn,  Suppliers of ball bearings, here in Australia, also sell just the balls. Those in the UK should also do the same.

Is it possible to use a standard ball bearing with the same OD and make an insert for the centre that will engage with the location pins ?  Or a smaller bearing that will accept the location pins and make an addaptor for the bearing OD ?

Edited By Paul Lousick on 24/05/2022 12:58:55

Good afternoon, Peter,

Some time ago I needed some 2.5 mm balls to repair the mechanical stage on a microscope.

The local bearing stockist was very happy to supply me except that he said 'You'll have to have 250-off to get over our minimum order value'.

Don't all rush to ask for some of the unused stock - they've disappeared into shelf-oblivion!!

Best regards,

Swarf, Mostly!

I have seen that pattern of bearing mentioned somewhere with a horological connection, but can't remember where. I must say that I'd be inclined to replace them with conventional small unshielded ball races, or ceramic ball ones, with the grease washed out (not ultrasonically cleaned). Someone in Australia did extensive measurements of friction of standard ball races and found they compared favourably even with jewelled bearings. Seems to me to be no advantage in only having balls below the pin, the ones above won't be carrying any load so in effect "won't be there".

I’m afraid it doesn’t answer your question, Peter … but I was interested to see that your bearing supports are similar to those on the Robert Bryson clock : **LINK** https://www.nms.ac.uk/explore-our-collections/stories/science-and-technology/congreve-rolling-ball-clock/

MichaelG.

.

Edit: __ more relevant though, is the fact that I recognised that style of bearing … and a Google search for “four ball unipivot bearing” led me to this page, where such an item is [poorly] illustrated:

https://fromvinyltoplastic.com/tonearms-101-an-introduction/

Personally, I think it’s a bad choice for the arrangement in which your clock uses a pair … gravity is in the wrong direction, and therefore the correct axial adjustment will be very critical. 

Edit 2: __ Clearly John Haine is thinking along similar lines.

Edited By Michael Gilligan on 24/05/2022 13:08:54

Thanks all. I am not sure that new individual balls are going to be the answer, as the outer "shield" of the bearings looks as if it has been inserted in the same way as conventional bearings - and removing it will probably be a destructive process. I suspect if I need new bearings Paul and John's suggestion to replace them with conventional bearings and modify the support pins for the ID of the new ones is the most sensible route.

Yes John, I have seen the papers on running small bearings dry and clean in clocks, and will be treating these bearings ( and the conventional shielded one on the escapement arbour) to a good flush out. I suspect the reference to similar bearings in a horological context you mention may be the Eureka clock bearings which come in two and three ball styles with two balls below the pivot and one ( in the three ball arrangement) above. Those however are loose balls retained on one side by a glass plate.

Michael, thanks for both the pointer to the Bryson clock and the bearings used in tone arms. As you say this seems an odd use of the design, and if a problem I will replace ( as above)> This clock is much later than the Bryson one - it's a Dent 1950 reproduction - but you can see where Dent got the ideas from, this one has the same finials. I have every sympathy with Darren at the Scottish museum. I have never worked on a mechanism with so many interacting adjustments - but then I don't do steam engines! Setting up the clock is an exercise in complete frustration. Hence the decision to pull it apart and fix things.

Thanks again.

I recon that when you replace the shaft with one that has hardened ends everything will be hunky dory. The balls and outer race are hard already and just need washing and relubricating. I have seen lots of this type of bearing in aircraft instruments, they are very low friction.

Aha! Peter you triggered my memory, it was on a Eureka clock brought along to an AHS meetup.

I've found that if I just need a couple of balls I buy an unshielded ball race and press out the cage, move the balls all to one side and remove the inner race. Simples. The interesting thing I've found is that metric ball races often have Imperial sized balls ! This may be because the machines that make the balls were originally imperial and they never bothered to change the design but there may be other reasons.

Anthony Randall wrote several articles in the BHI journals about his experiments using ball races in weight and spring driven clocks.

The Eureka clock, which has a horizontally pivoted balance wheel, uses three steel balls in each pivot and these provide electrical conductivity in the circuit for the drive coil. This produces a degree of electrolytic corrosion and rusting of the balls and unfortunately ceramic balls cannot be used to cure this condition.

CS