Hi Northern Hewer,
Up until now we have been discussing buldings experiencing fairly static type loads or loads regularly applied from the same direction e.g. the prevailing wind. You have now crossed the threshold into an entirely different field where reciprocation and rotation will result in frequent stress reversal on joints. There is no room for any kind of slop in joints on those types of structure and hence joints will need to be fashioned to take regular tightening up into account.
To explain further, for example, the spokes on a gin wheel or donkey wheel will change from being in tension to being in compression as the spoke moves from the 6 o'clock position to the 12 o'clock position thus depending on the speed and regularity of the the turning operation the spoke joints will become quite vulnerable to wear and deterioration and will quickly pull themselves apart if reliance is made on simple dovetail joints.
You should send a measured sketch copy of your joint configuration to Jack to add to his collection.
Regards
Ken Hume
