Perhaps I should introduce myself. After lurking here for nearly a year, purchasing an IH manual mill and later completing the CNC conversion from an IH kit, I finally have some comments and questions for yall. Cruiser, Bob, and Runner have nearly become household names to me, yet you guys have never heard a peep from me, so here I am. Bob, I love your web-blog, keep up the great work. Cruiser, nice work on the belt drive and the z-axis mod. I am located in Bend Oregon, If you ever come over to go skiing, drop me a line, and we can have a beer.

I am an ameture machinist, having had an introduction to machining at Oregon State University (GO BEAVERS!!) where I studied to be a Mechanical Engineer, I now work for Cessna Aircraft here in Bend.
I have many questions to ask/answer, and a lifetime of tooling crashes ahead of me. (shockingly none so far.....crap....well that goofed it up..)

OK, enought rambling. Backlash..... I have approximatly 0.003-0.005 system backlash on my x and y axis, and approximatly 0.010 on my Z. the "backlash" is of course not due to the ballscrews, but rather the torquing of the ball-screw required before the axis slide begins to move and the screw actually begins to turn in the ballnut. I refuse to turn the backlash compensation in Mach on, as the stop-go movements are rather annoying, and certainly don't do any favors to your program run time.
I have set my gibbs so there is approximatly 0.0005 in lateral movement across the joint when the table is forced in-plane. (ie x-axis is pushed in y direction, and the movement at the end of the dovetail is measured with an indicator.)
So my quesiton is this, a certain bit of "torquing" in the ballscrew is inevitable prior to movement, but is 0.003-0.005 backlash excessive? If i interpolate a 0.5 inch hole it reliably comes in at 0.493 +_ 0.001 and round as can be. Repeatablility is outstanding, but the inability to hit the desired dimension is irritating. (note: I have double checked the actual cut width of the cutter used, as well as trying different size and shape holes.)

Does anyone have any suggestions for reducing this backlash without excessively loosening the gibbs.
Are the gibbs adjustments really that much of a dance to achieve optimum adjustment?
The Z axis is un-copensated for its weight, and the gibbs are set so there is about 0.001 "rock" when a lifting load is applied to the nose of the head. (any looser and the spindle would come out of perpindicularity alignment with the table.)

If any of you guys familiar with the mill have any suggestions for me, I am all ears.
Thanks!!!

JeepJake