An X Y Z R Table: the Z axis

I have most of the pictures, and will reconstitute the ones that I do not have.  It's a very different way of doing things for this part, because I decided to spend money rather than get the whole thing done as cheaply as possible.
So what did I do?  Instead of the table resting on roller skate bearings, I decided to use linear bearings and supports.  I have rods and linear bearings holding up the table, and will use the 135 in-oz steppers to control it.

I had to decide how to do this.  The best way that I thought of was to make a framework of 1/2 inch aluminum 1 1/2 inches wide. 

The major idea is to make a cage for the table, and then suspend the z axis from that cage.  Cross bracing will be added as needed, but right now, it's not in there. 

First thing is the Z axis, and the idea is to figure out how high to make this.  What I wanted to do was to make the top limit of the table roughly equal to the travel.  That means, a 6 to 7 inch z axis reach, and I need to also consider the height of the rotary table.  (do please see that section).
Well, this is roughly what I want to do, height wise.
First, cut all the aluminum, drill and tap for the 1/4 by 20 socket head cap screws that hold it all together.
This is roughly how it goes together.  Note that the way the bolts fit.  They will not run into each other.  Been there, done that.
The completed cage.  I will add a piece of angle (as you see, but longer) to go across the top.  The bottom carriage has the complete assemblies as detailed in the previous sections, but also has the edges built up with the 1/2 inch aluminum bar.  That clears the adjustments for the bearings.
Along the top, I drilled holes for 1/4 by 20 capscrews, each 1 1/2 inches apart.  They will be for the angle.  Yes, they will all be tapped.  I just need another hobby.
Fortunately, I bought a "hand tapper."  It allows the tap to go in straight, without a problem at all.  The only thing that you have to realize is that the lever action of the handle will make it easy to over torque a small tap, so you do need to be careful and develop a touch.
Tapped, all that's needed.
This is not the first piece of bracket, but it's the one that I went out and bought.
The Z axis is a flat plate with two end pieces.  This is the bottom end piece. 

The two holes are for the linear bearing rods, and are drilled as precisely as I could.  It was not good enough, though.  Errors happen.

Now the counterbored hole is for a homemade thrust bearing.  First, consider the roller skate bearing.

Here's a close detail of the bearing holder, it has two steps.

First, you put in the skate bearing.  This takes care of the radial loads, so the Z axis cannot wander in the X or Y direction. 

Next, you add the bronze bearing.  I probably needs to be something other than bronze, but that's what I bought.  Note that the bearing inner diameter is larger than the acme screw that goes through it, and also bigger than the inner race of the ball bearing.

Here's the rest of the assembly.  The aluminum collar is fit to the inside of the thrust bearing (surplus).  The inside diameter is bored to 8.0 mm, which is is the inner diameter of the skate bearing.  You can guess the way this goes together.

A closeup of the acme thread and the bearing collar.

Put the bronze bearing on the thrust collar.

Then mate the whole assembly together.  The bearings run on the bronze collars, which could be replaced by steel if needed.  The aluminum thrust collar cannot rub on the inner race of the bearing, since it goes only part way through the ball bearing assembly.
More to come....

 

Go to part 2