Hi Kevin,

I used to use a short length of stiff rubber tubing (similar to the reinforced sort used on cars for flexible brake hoses) which was a tight friction fit on both shafts. This worked a treat giving a bit of vibration isolation and alignment, and it never slipped or broke. These were fitted to both X motors and the Y motor. Z is belt driven.

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After many, many hours of use I decided it would look more professional fitting a coupling so went for the spiral aluminium type. One of them broke eventually, and the problem with them is that it is not obvious that they have broken as they can still transmit drive to the ballscrew most of the time.

I then fitted a larger diameter one, and this has been running for some time although the other day I was looking at them wondering how long they would last.