I was really sick yesterday and only got out of bed for an appointment. Thank goodness my wife is very understanding! This morning, I felt much better and decided to make some progress and write an update.
At first I was going to try working on the Z axis without removing the head of the machine, but the more I thought about it, the more I realized that I wasn’t being practical. The head is really heavy, and trying to get the machine put back together with the head on would be a headache. With the head removed, I removed the four screws holding the lead screw in the back of the machine and the eight screws connecting the head slide with the screw. Everything on this machine is also pinned together, so it takes some wiggling to get the parts loose.
With the lead screw on the bench, I had to remove the bearings and blocks. This sounds easier than it really is. The important thing is to be smarter than the machine. Resist the urge to 
use a hammer to bang on things! In the photo to the right, you can see the original lead screw assembly next to the new ball screw. There are two small problems that you need to tackle in order to get this put back together. The first issue is the removal of the bearing retaining collar from the “south” end of the screw.
This collar is held in place by a pin, which you can see in the following photograph. In order to remove the pin you will need a hammer and a punch. I cheated and used an old nail set. Be wary of two things. First, the pin is tapered, so try to find the small side and punch it out. If it doesn’t start moving, try the other side. Don’t use a lot of force unless you are sure you have the right side of the pin. Second, be careful not to mushroom out the head of the pin, as it wont go anywhere if you do. There is a key in the screw for the gear, and you should be able to gently tap it out with a hammer.
On the “north” end of the screw you’ll find a bearing which needs to be “recycled” 
on the new screw. Bearings are pretty fragile, so the best way to remove the bearing is to press it off. If you have some sort of puller, good for you! If not, rotate the screw until the block travels all the way to the end. Keep turning the screw and the block will press the bearing off.
The bottom support has a thrust bearing top and bottom that you’ll use on the new ball screw. Reassembly is pretty straight forward. I’m going to stop working here for a couple of reasons. First, I noticed that the thrust bearings were dry and I want to grease everything before closing up. Second, I’m also going to install a gas spring, third, I want to run the Z axis stepper motor a couple of times to to make sure everything looks good before I close up the back of the machine. This means I need to do some soldering. With luck, I’ll post about the electronics today or tomorrow!
