Fanuc 10m feedrate affects circle size

Hello.

I have problem with mori seiki mill. When doing circle (G3G91I-5), it is too small if feed rate is high. If slow feedrate its ok. Error seems to be quite linear, example with 3000mm/min D10 circle is 0.5mm too small, and with 100mm/min its good. Hole is not oval, its just too small. G61 is enabled (no affect). Backlash checked. Also if i make square with g1 its allways same so feed does not affect on that.
Any parameters related to interpolation or servos which i can adjust? I tried tune acceleration parameters but no affect...

No, that seems about right to me, especially on older hardware.

You have to give the tool time to cut rather than flex, and the servos and cpu need time to process position. A hole that small will do that.

Newer controls have greater control on position, but they too will slow down more in corners/small circles to get the intended result.

If you were cutting a 100mm circle, you would notice the error is much smaller at those feedrates.

In addition, while you program the center of the tool to go 3000mm/min, at smaller circle diameters and relatively large tool diameters (say a 5mm tool interpolating a 10mm hole), the outside of the tool is going much faster than 3000mm/min. I've seen someone post the math on it before, I am not going to go looking for it right now.

Yeah, sounds like normal deflection but without knowing the cutting parameters it's hard to say.

Raise up the tool so you are just witnessing the cut- say around .025mm or less DOC. Measure your diameter with the higher feedrate.

Take the cutter push-off out of the equation, see how much is the machine and how much is the cutter.

It is not deflection becouse it makes same even it is not cutting anything. I think dandrummerman is correct on that so it is just old and cannot calculate fast enough...

It's just the result of how servo systems of that era work. Keep in mind that we are discussing a control and machine that is 30 or so years old and was just one step above the entry level Fanuc offering at the time.

The result you are seeing is caused by servo lag. Lag is the error between where the control has commanded the servo to be and the physical position of the servo. The greater the commanded speed, the greater the lag.

Acceleration and deceleration also factor into this. Less so on circle cutting, much more noticeable in linear moves with direction changes. If you program a square and try to run it at high feedrates you will get rounded corners unless using exact stop check (G61). I don't know a figure for the 10M, but I did some testing on a Yasnac MX2 (slightly older than a 10M) and at 140IPM there was approximately .03" radius cut on a programmed square corner.