Next I indicated the second X rail using the master rail as a guide. I got these parallel to about 0.0002 inches I estimate.
With the X axis rails mounted I moved on to the the Z axis mounting plate. I used 1 inch thick cast tooling plate to build the Z assembly. The plate is flat to about 0.002 inches over its 16 inch length. I may lap it at a later time but I have yet to see it cause any problems. I printed a paper template and glue it to the plate. I then used a punch to mark each hole and drilled all the holes with a drill press. My drill press has a reverse switch and a momentary run switch so I can easily power tap. The Z rails are NSK LH25 rails and mount with 1/4-20 bolts. I used a gun tap to thread the holes.
I mounted the Z axis plate to the X axis rails and then mounted then Z axis linear rails to the plate. I used the smaller granite surface plate to indicate the master Z rail in then indicated the secondary rail in from the master. Like the X rails these Z rails are quite straight. I squared the Z to the X axis at this point using a ground angle block and my indicator. I did this by rotating the Z plate slightly and sweeping the indicator back and forth against the angle block. I acheived a squarness of about 0.001 inches over 6 inches and decided this was good enough. I then tightened the Z axis plate against the X axis trucks.
At this point I tried sliding the Z assembly along the X rails and noticed no binding. You can feel the preload in the rails though and it takes a little force to move across the X travel.
I then started on machining the spindle mounting plate. I made a paper template once again and drilled and tapped the needed holes. This plate required counterbores and machining as well which was done on my X2 mill. I ended up breaking a plastic gear in my X2 and had to rebuild the spindle during this job. I replaced all the gears with metal and swapped the bearings to sealed versions as well.
I mounted the spindle plate to the Z axis rails and checked for binding but did not find any. I made another paper template and drilled the holes in the spindle clamp. The back of the spindle clamp was lightly lapped and then the spindle was attached to the spindle mounting plate.
Continued in next post....