Hi
I have a Hameg HM-408 scope that uses extended shafts to go from the front panel to the switch / pots mounted inboard on the PCBs. These shafts are 2mm dia and the switches / pots are 4mm dia and are connected via flexible couplings.
Five of these couplings have failed and so I'm looking for suitable replacement couplings that will connect to the 2mm shaft on the control knob and onto the 4mm shaft from the pots / switches.
Can any point me in the direction of possible replacement units?
Do they have to be flexible because they pass through an "S" shaped path through screening etc? My first thought is fine nylon cable wrap, somehow stiffened up with something as a core.
McMaster-Carr. But maybe only available in the States and I don't know where you are. Eric
Well, H. H. Smith used to make a line of couplings (and flexible shafts). I'm uncertain where to find them nowadays.
Most flexible couplings are intended for motor shafts, will be VERY expensive for your application. It's possible to buy speedometer cable by the foot, and anyone with a lathe can make epoxy-able ends for your choice of shafts. I've done that... only worthwhile for long runs, of course.
Do these couplings just need to have compliance for minor misalignment or shaft position offset? This kind is good for position offset
and the universal-joint and spring types only handle angle misalignment. Two of those with a stub shaft between is how they handle offset.
What do you mean by "failed"?
If the parts that clamp onto the shafts are good, you may get by replacing the flexible part. Take some flexible metal strip, or piano wire. Bend it in a loop big enough to flex, but small enough to fit in the space allotted. Solder it to the metal clamps.
If they're steel, solder should work.
If aluminum, there's some stuff called Welco 52.
You won't need much, so you can buy similar stuff at most any hardware store or big-box store without breaking the bank.
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If you can find a 2mm flexible coupling, you may be able to just drill out one end to 4mm.
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You may be able to find a spring that will do the job. For low-torque applications like pots, maybe a ball point pen spring and some epoxy. If the spring is a tight fit on one end, it will slip before the epoxy breaks on the other end...maybe...
How much flex do you need? Spiral cut flexible coupling might be cheap.
(As someone said you might be able to drill out one end.)
George H.
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