Dahui,
I figured out something helpfull on my Tri-Power for reducing the table rotation around the z-axis. Having noticed the rotation when boring a hole on the lathe and then reading this thread I decided to try and quantify how much rotation my machine had and why it happens.
I set up a test indicator on a magnetic base on the table indicating on the outside circumference of the lathe 3-jaw chuck at the lathe center-line above the table so I could move the table in x and read the y movement.
Starting at the right edge of the chuck I moved the table left about .1 inch and zero'd the indicator. Further movement to the left showed no indicator movement as expected. Reversing the table movement to the right showed about .005 movement away from the chuck that then stayed at .005 with further rightward movement. Moving the table back in the leftward direction brought the indicator back to zero repeatably. The reason for this movement is rotation of the saddle in the x dovetails driven by torque from the offset lead screw reaction with the friction of the dovetails. Properly adjusted gibs SHOULD eliminate this rataion.
Note that when I measured the .005 displacement the left edge of the table was about 2 inches from the face of the chuck. The reason I point this out is because I believe the table is rotating about the intersection of a line drawn from the back left to the front right with a line from the front left to the back right of the dovetails. So if you move the table under the chuck and make the same measurement the displacement is much less because you are closer to the center of the rotation and the y component of the rotation is less because of the angle.
Now for the hopefully helpfull tip. When you move the table from right to left the offset acme screw causes the table to rotate clockwise. The rotation is limited when the rear right dovetail edge and the front left gib strip edge come in contact with the ways. At the same time, the rear left dovetail and front right gib strip are actually pulled away from the dovetail. When you reverse the table direction the opposite happens. This can be used to advantage when adjusting the gibbs!
So the trick is to tighten the right gib strip after moving the table to the left and the left gib strip after moving the table to the right. Using this method I didn't have to snug up the gib at all to get less than about .0003 of displacement using the above measuring method. In retrospect I can see why I had trouble adjusting the gibbs before. If you adjust the left gib after moving the table to the left it will be to loose and vise versa.
I do have to mention that after using this method the table will run very smoothly and correctly for much of its travel but the last 5 inches or so by the lathe chuck will be a little tight. Tightness causes excessive x slop. Not to impressive for a brand new machine.
good luck!