The slotting is used WITHOUT the lathe under power, It is set in the compound in place of your tool post then it is brought up to the work mounted in your lathe check, faceplate
then the carriage is locked down and the cross is used to cut internal keyways or splines and could probably be used on some external cuts as well. It is hand operated with the attached
lever. As stated in the post I did cut the key way for my pulleys for a belt drive upgrade for my mini mill.
Hope this clarifies things for you.