Thank you all for you kind words on my work. The bulk of the praise should go to Gray, as without his excellent design work this would never have materialized. In use I have found there is a small issue with the accuracy of the end stop. Due to the long operating arm this is not as accurate as I would like. I have done some tests and am currently modifying the design to address this. I hope to have this completed in the next week or so and will send updated drawings to Gray as well as some more pictures..