Z-slide Limit Stops
 

The drawings don't explain this:


A & B are 5mm [5/16"] screws tapped into the back of the tube. They impact (seldom) against the bent tab C of the spider plate.

Position the screw heads so that:
a. The pinion does not run off the end of the rack.
b. The slide does not run out of the V-rollers
c. The gas spring does not reach its internal limits.

These screws were not defined in the drawings because of the unknown factors of which gas springs you are getting.

how many lbs does the gas spring need to be

To null weight of your spindle

correction; to balance the weight of your entire Z-slide including your spindle.