Getting machine tolerances dialed in after the build

[BillB]

Hey All, Need some input on dialing in things on my Sherline mill build.

When looking at the backlash I'm consistently having to hit 6 to 7 clicks with the jog increment when set to .0005 when switching from one direction to the other to get any movement on the needle.

Testing
Putting a .001 increment dial indicator on a fixed point on each axis and hitting jog increments here is where I'm at.

X
I hit .01 and consistently get .008 of table movement.
I hit .1 and consistently get about.075 of table movement
Im getting about .004 backlash when jogging back and forth

Y
I hit .01 and consistently get .007 of table movement.
I hit .1 and consistently get about.08 of table movement
Im getting about .0035 backlash when jogging back and forth

Z

I hit .01 and consistently get .004 of head movement.
Backlash on Z is all over the place when I jog in Z back and forth, but there is an anti-backlash kit from Sherline I need to order so not really focused on Z till I get that installed.

This mill is a lead screw machine and is a 1/4-20 thread so put in 20 for thread count in the configuration in the Wizard. The machine is not new but was not used all that much over the years. I never really adjusted it for backlash.

Test Cut
I've cut my 1st test part to see where I'm at for accuracy, even though I know there is backlash and something else that needs adjusting I still figured it would be a good idea to run a test to see where I'm at as a starting point.

Running Fusino for CAM and using the Centroid post-processor that is in the post list in the software.

I cut a simple 1 inch X 1 inch X .25 block, that I faced, then did a contour cut, with a .5 circular pocket.

Im - .004 off in X
Im -.004 off in Y,
only -.001 off in Z

The circular pocket is about .004 undersized and deviates quite a bit as much as .01 in diameter, however, a .5 K&S brass tube press fits quite well in it. BTW the material I have cut is a plastic urethane I custom cast years ago back in my day when i was in the toy industry. SO the press-fit would make sense, it was aluminum the tube would not fit for sure.

What are the steps to get this mill dialed into a more acceptable tolerance?

[Muzzer]

If it has lead screws rather than ballscrews, you could fit a second nut and put shims or a spring washer between them but that's polishing a turd and you will still see inconsistent behaviour. Hopefully you won't need much of a nudge to take the leap, get yourself some ballscrews and go the whole hog - plenty of examples to take inspiration from out there!

It's true that you can play with backlash compensation in the CNC12 software but there's really no substitute for removing the backlash from the mechanism itself, otherwise why would anyone bother with precision ballscrews etc?