poor surface quality

Hi Peeps,

Im pulling my hair out trying to debug a poor surface problem. I have a LinuxCNC retrofit Haas mini mill. Dimensional accuracy is within 5 microns, perfect. Backlash is around 3 microns.

The problem is the even faceting im getting, this is only on round or any move that needs the x and y axis working together. Straight lines in x and y are a nice and smooth surface finish. I have attached a few pics for reference. 

the cutting strategy was adapive clearing with 0.5mm stock to leave cleaned up with a profile toolpath

The square was oriented with the points facing north, south, east and west, forcing them to be cut using both servo motors.
I'm using AC servo motors with 10.000 steps per rev. So 1 micron per pulse.
I'm running a 2 ms servo thread, probe basic on linuxcnc 2.9
for this cut I used 0.001 tolerance and tried smoothing on and off with no difference. I also used G64 p0.01 makes no difference

if you look at the images you can see the faceting lines, they all measure around 1.5mm between each line.

any thoughts?


 

I had similar problems with my servo system, and solved most of it by tuning the servos better. A loose servo control loop will look precise and accurate, until you put it under load. Can you rotate the servos by hand, at all, when they should be "holding"? If so, retune them.

I will take the covers off and give this a try. Thanks man.

Hi tommy. They are ac servos all connected to the same 240v supply. Would the tuning be done via lunuxcnc or on the servo amp? They are step and direction drives. Thanks

Which type of servo drive do you use?

They are lichauan a5 drives

Hi tommy, 

The voltage was the same at both drivers. I have dug a bit deeper and used Halscope and probed 

Joint.0.motor-pos-cmd against hm2_7i95.0.encoder.01.position

For both X and Y, I cut a few circles using arcs, and this is my result. Looks like the motor isn't keeping up with the encoder?

I wasnt sure what /k to use, so I have attached two screenshots, one all even /k and some scaled to fita better curve. This is all new to me so apologies in advance. 

I'm using Step/Dir Servos, I have just temporarily fed the endcoder back to LinuxCNC for testing. 
Im using 1kw ac servos by Litchaun 4NM the machine is a Haas mini mill. any thoughts?
   

As had been suggested before, it looks like the drives themselves need tuning.