My "normal operation would be to elevate the mill only 1/4". It is reasonable steady but depending on the position of the casters can get shaky, but cannot fall over.
I was only extending the scissors because I had a request to see them extended. Obviously I did not "think" it through but just started cranking.
I diffidently would extend the lower channel iron if I were ever to need to raise the mill more than 1/4".
And thanks again everyone for your comments, I do hope this thread might help someone avoid killing themselves.