There seem to be two types of motor-screw couplings for CNC - Oldham couplings where there is a sliding disk,and a type whose name I don't know with spiral cuts in them.
Both seem to be very expensive for what you get!
Anyway, can anyone tell me what they actually do -the Olham couplings seem to compensate for slight misalignment between the drive and driven shafts, but do the other ones do the same? Which is better?
Thanks,
-- Peter Fairbrother
Oldham couplings are not expensive, look in Arc new catalogue and you can get both halves and the torque disk for under a tenner. I have to make certain specials and believe me if could buy them for the amount of work involved I would.
Oldham couplings do compensate for misalignment and because they are separate it's not a continuous twisting action like the spiral cut type. If there is any large misalignment these will destroy themselves over a period of time.
John S.
--This latter type is called a helical coupling; invented in WWII for use in bombsights, IIRC. The process for making them was kept a trade secret for over 50 years. They're very neat couplings because they have
*zero* backlash, so they're very useful in things like cnc machines. The biggest company making them is Helical Products. There's one other, newer company as well but the name escapes me at the moment. If ya ever see 'em surplus grab 'em; they last forever..
I have used Oldham couplings for my various projects and have found them to work well and reliably. Both types are "zero" backlash - although in reality, there is no such thing - the sliding plate in the Oldham couplings will have some degree of give in it, and the spiral type couplings are effectively coupling the two shafts together with a spring that can wind up/unwind to some extent. So both types will exhibit some backlash, depending on the load and the size of the coupling.
Regards, Tony
ISTR reading somewhere that the Oldham coupling is used where there is a chance of only a lateral mis-alignment whereas the spiral (helical, surely?) coupling is used for angular mis-alignment and that neither coupling is suited to the domain of the other.
References? Where did I read this? Sorry, no idea!
True - the Oldham coupling isn't good for significant angular misaligment, and the helical ones are no good for significant lateral misalignment. Both will tolerate a small amount of the "wrong" kind of misalignment though.
There are some couplings that are designed to take both types of misalignment - for example, the "Uni-Lat" coupling (e.g., RS part number 748-421) - but these are somewhat more expensive.
Regards, Tony
Googled for Unilat and found this which seems to be a good summary ...
But, but, but ... we're engineers, ain't we?
The manufacturing of our own Oldham style couplings must be a distinct possibility.
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