What happens when load inerta ratio parameter too low?

[Hermle UWF851]

I have a new VMC with an Oi-MC. All three axis "hum" when standing still. Like they are fighting to hold position. I was told by the manufacturer to lower parameter 2021 until it goes away. I have dropped them from 600 to 100 and it helped but is still there sometimes. How do I know what is too low? What else would cause this "hum"? Of course when the dealer comes, it don't do it much if at all. Then the next day while I'm drilling a hole, x is screaming while I'm drilling. I don't machine heavy. All our stuff is light cut precision type machining.

Any advise is appreciated. Thank you for your time.

[f-bu]

PRM2109, all the axes, try 24, 32 or 40

[CHAD LAWSON]

make sure when changing any servo tuning parameters you double check the accuracy of machine when done. i have seen fanuc come in and tune machines to run quieter but when they left the machine accuracy was way off. Many times one servo parameter adjustment often leads to another. One thing i have noticed on cheaper machines all axis will have the same load inertia setting now im no engineer but a b-axis on horizontal surely does not have same load inertia as y. Some machine tool builders do not optimize servo parameters for enhanced performance at the factory.

[Hermle UWF851]

Thanks guys. I will have to get a ball bar or laser guy in when I do this. That's why I was wondering what these parameters do when too low. I didn't want to affect accuracy. I'll then try PRM2109. I'll post what I find.

[CHAD LAWSON]

I do not have a ball bar so what i would do is cut a circle and measure it for true roundness. You could also check z by checking the depth. But i usually right an accuracy program and place a tenths indicator on the axis and check each on this way. It should repeat to zero but some machines have lower tolerance levels such as +- 3 tenths of an inch. But if you see this i would change your back lash settings. You could look at changing your parameters from a bell shape curve to a linear curve or vise versa. Also does this machine have linear scales because i have seen this when scales are contaminated unlikely for all axis but just a thought.