Dave, I haven't got a stop at 90deg but was intending to add one but find it so quick to just square it up with a small square and lock it in place that I probably wont bother. I have PM'd you about the CAD files.
Tony, the original spirals were too big to fit on the right hand side where the locking knob is so I made my own, just a turned bit of wood with an off center hole in it.
John