Well I never thought we'd end up with 8 pages of guff on this over three weeks, with an assortment of new/abandoned circuit designs and quite so much head-scratching!

Anyway the machine is now back together and appears to be working every bit as well as it did before I decided to replace the microswitches with inductive proximity sensors. The real excitement is that I can now see how well the all-aluminium Z axis behaves compared to the old plywood prototype I've been using for the last year or more.