Hunting for the cause of the hunting

We had been noticing that when water, and therefore power, is short the mill speed varies, slowing down once per revolution of the waterwheel.

Eventually, careful observation showed that the problem was that the angled gear teeth on the pit wheel, which shares its axle with the waterwheel (visible at the left of the upper picture and just seen over Neil's right shoulder in the lower) were not engaging at a constant height with the matching angled teeth on the wallower (showing just over the beam in the upper picture and half visible at centre right of the lower picture).

With the wallower higher, the coupling is slack.  When the wallower meets the pinwheel lower, there is considerable pressure exerted due to the angled gear faces.  The top of the wallower appears to move from 1cm below the top of the pinwheel to 2cm above.

Clearly something has run a bit out of alignment.  We made an attempt to help matters by twisting the pinwheel slightly on its axle and repacking the wedges.

This weekend there has still been some hunting, but we've had a bit more water so it has been less of a problem, so not sure if we have really improved it.