[Rich05]

about a 5" hole, in aluminum 2" deep.

Feed rate 30ipm, depth cut .1875", rpm 3250, high helix endmill 3 flute.

also using 2 finishing passes at final depth of .010.

The hole is off by .020. Do I need to tune my motor controllers better?

What accuracy should I expect?

[RustedOut]

Is this on a new mill? Have you measured and corrected for the actual ball screw travels? If an older mill, you may have some slop in the nuts, bearings, nut mounts or some other place.

I never rely on the travels to give me an accurately round hole, but get close then use my boring head. I just noticed a few days ago my X and Y travels are off, so I got to measure and correct them.

Bob

[AiR_GuNNeR]

Backlash can also be a culprit.

[txcncman]

about a 5" hole, in aluminum 2" deep.

Feed rate 30ipm, depth cut .1875", rpm 3250, high helix endmill 3 flute.

also using 2 finishing passes at final depth of .010.

The hole is off by .020. Do I need to tune my motor controllers better?

What accuracy should I expect?

"The hole is off by .020." What does that mean? Off location by 0.020"? Off of diameter by 0.020"? Out of roundness by 0.020"? What machine? What size tool? What RPM? What tool material?

[jrods2]

if you can't cut a circle within .0002 you got problems.
1. check the travel of each axis with an indicator then move table back to where you started. If indicator reads back to zero alls well if not you can adjust out some of the backlash but you will lose some on distance travel.
2. Call a cnc repair shop & have them check your machine. When I bought mine and had it installed they checked everything and adjusted as well for a reasonable soom of about $120 an hour

[Dean Guilberry]

Also look at your motor to shaft couplers and make sure there are no slippage. I hunted for a bit to find slippage once. It was undetectable to the eye or even by marking on the shaft but once I took the coupler off and reseated it and properly torqued it no more issues.

Just a thought.