Taking on board the good advice offered by so many Members, I scrapped my first attempt at a dept stop and up graded the whole thing.
The end result has been much more satisfactory all round, with the error being reduced from 6 or 8 thou to I or 2 thou, which is good enough for my needs
I would like to thank everyone for their input.
I will try and put photos in my album [sometimes it works, sometimes not ]