[Vogavt]

Not sure what's going on here but I've measured the Z-axis movement with a dial indicator and have gotten it to repeat positioning accurately. I've adjusted the backlash the best I can and finally utilized the backlash offset within Mach 3. I can issue code and have it move up and down to within 1.5 thousandths at any (+) or (-) I give it and yet always return to zero. All of this is without any load, just free movement.

I'm milling a 1/4" piece of aluminum in four passes at 0.0625" each pass. However each pass is measuring with a digital scale at 0.0675" each. I have bridges placed at strategic spots to keep the piece from falling through on the last pass. I plan to manually remove the endpieces with twist and burnish off the remaining portions, but at the last pass I don't have enough material left to hold it.

I THINK I've got the steps/unit correct because of the repeatibility, but now I'm concerned that maybe the dial indicator is way off. I think it's that, but not sure.

With all that being said, is it possible that under load the head can drift down or is it possible that the process itself if pulling the head in a downward direction? If so, how do I compensate accurately?

Sorry I don't know any other way to put the question.

Noob out......

[dalvinder]

as the machine is moving in Z axis and showing repeatability so the steps should be what they are supposed to be.No back lash is there and even if the backlash is there steps are going down so even that dont have a role to play.only thing left is pitch error if thats there try a plunger dial with 1 micron least count and use handy pulsar and origin Z axis and move Z axis by 1 micron and go down till 1mm every time 1micron at the end of 1mm check the on screen value for Z and the dial if they are same then it could be the machining process.

[OldWrench]

Try leaving .005 for finish cut between each pass, make a finish cut to remove this and measure. If .0625 is the amount of stock removed, could be your method of milling.

[Vogavt]

could be your method of milling.

Can you explain this further?

[Khalid]

In my case, z-axis get down when i m doing 3D milling. But it is workin good when i milling 2 or 2.5D. I just decrease the IPM from 15 to 10 IPM for the Z-axis and its working will n 3D.