Finished the 3 axis and fully tested.
It's a budget conversion but with pretty good specs.
X axis travel 16", Y axis 8". Z axis around 15"
rolled ball screws on the x and y axis, Stock acme on the z.
Double spring preloaded ballnuts on the x and Y axis, an adjustable backlash nut for the acme z axis.
Direct drive with large a Oldham coupling for the x axis. The coupling also serves as the bearing preload nut with a center locking setscrew.
Belt drive y axis using Gt2 3mm pitch pulleys and 6mm belt at a 2-1 reduction. The large pulley also serves as the bearing preload nut with center locking setscrew.
Belt driven z axis with 2-1 reduction gt2 3mm pitch pulleys and 9mm belt
I added a 3rd speed which is a direct to spindle V belt that raises top speed from 2000 to 3400 rpm. It is also very quiet as all gears a bypassed.
It is a 10 minute job to convert back to the factory geared 2 speeds. I added quick knobs to remove the belt/gear top cover to make speed changes faster.
The head is counterweighted with a 2-1 compound pulley. I use 50lbs of which like 100lbs at the head and with the lead screw disconnected I can easily slide the head up and down the column by hand.
I'm using a xylotex drive box with 425 oz steppers. These motors are not exactly speed demons but x and y axis are dead reliable at 75 IPM with tight gibs and bearing preolads. The ACME Z AXIS is limited to 20IPM.
Backlash for the x axis is .0003". I am very happy with the y axis Gt2 belt drive as it is only at .0005" backlash and very close to the driect driven x axis.
The z axis with acme screw is .002" or just under that.
I first tried setting up the motors with my laptop and MACH 3. I thought perhaps I had some big issues with the motors as they were very rough.
I switched to the desktop pc I use for my mini mill and every probelm disappeared.
I still need to add limit switches and finish the 4th rotary axis.
steve