Oldham Couplings

[Tim StevensParticipant @timstevens64731]

The latest query for me is to do with an Oldham Coupling on a USA-built Essex car from 1918. The coupling connects a sprocket to the dynamo-cum-oil-pump-cum distributor.

The tongues each side are steel, and tapered slightly. The central disc is brass, and has slots to match the tapers, and these slots extend about 12mm wider than the tongues.

What I ask you to do is to think about these features of the design, and comment. Then I will chip in with my own thoughts, and, of course, a clue about why I am asking.

Thanks to all you Oldham Coupling enthusiasts.

PS should it be Oldham's, I wonder?

Tim

[Tim StevensParticipant @timstevens64731]

A detail design question

[Neil WyattModerator @neilwyatt]

The slots have to be longer to give engagement with imperfect alignment, which is to be expected if an oldham coupling is being used.

I assume the taper on the tongues is to deal with angular alignment.

I have to ask, is this a particularly ill-built or flexible car?

Neil

[Tim StevensParticipant @timstevens64731]

The car is a solidly built big four-cylinder inlet over exhaust tourer. The motor is flexible, but otherwise I would say no, not ill-built at all.

And I don't think angular misalignment was a problem. The sprocket runs in the crankcase which also carries the dynamo etc connections.

More later when other have had a think.

Tim

[Perko7Participant @perko7]

Similar couplings were used on many budget-priced n-gauge locos in the 80's. They allow a degree of horizontal misalignment (not angular) as the brass (or in n-gauge locos nylon) centre is free to slide in the tongues machined on the driving and driven plates to take up the misalignment. The driving and driven tongues would normally be at 90 degrees to each other to permit this. Provided lubrication is maintained they would seem to have a relatively long life.

[Maurice Cox 1Participant @mauricecox1]

The old teleprinters that I used to repair had two of these; one between the motor and the main shaft, and another to drive the demountable keyboard. Originally the disc was of a brown fibre substance. By my time they were nylon. They wore out quite rapidly. Some were so worn that the two tongues were opposite each other instead of at right angles. Perhaps the tapers on your example were to eliminate backlash by advancing the disc toward each other, pushing the tapers deeper in the slots, reducing the clearance?

[SillyOldDufferModerator @sillyoldduffer]

Maurice's mention of these couplings in teleprinters stirred an ancient memory. The fibre disc was designed to break (like a shear pin) in the hope of preventing damage should the mechanism jam. (Useful to know this when checking out a time-served teleprinter before buying it. )

Possibly the brass disk in the old car is protective?

Dave

[Alan JacksonParticipant @alanjackson47790]

Early Manx Nortons had oldham couplings and that was a testing environment

Alan

[Howard LewisParticipant @howardlewis46836]

Very many fuel injection pumps on Diesel engines were driven by a similar coupling with steel flanges driving onto, and by a Tufnol type material with four evenly spaced slots, to match the straight sided teeth. Despite the torsionals from the fuel pump coming one way, and the crankshaft torsionals coming via the timing gears, or chain, they used to last a long time.

More recently, this type was still being used to drive Jabsco Sea Water Pumps on marine engines

There was another type of coupling in which the steel elements had a "tooth"section similar to a knuckle thread, with a similar shape to the fibre or hard rubber insert. The clever ones had a difference of one tooth between the driving and driven sides, so as to allow a vernier adjustment for magneto timing.

Howard

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