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VF4 Chatter While Interpolating Holes

Blackhawkxp

Plastic
Joined
Nov 14, 2018
We have a 2011 VF4 that seems to get a bit of chatter when we interpolate holes. It is always seems to show up at 11 o'clock and 5 o'clock if it was a watch face. Not sure if there are some parameters that will help minimize this? I assume there might be a bit of backlash when changing directions on either X or Y that might cause it? Its not horrible but it is there.
 
Schedule your breaks at those times.

Boom!



....but seriously, what size holes does this become noticeable? Does 'time' change to 1 & 7 when you cut clock-wise?

TH
 
Nice! I would say over 2". It seems when it is transitioning in X/Y to different direction it shows up. Only in those 2 spots though. I'm not sure on the direction change as we usually climb mill.
 
Nice! I would say over 2". It seems when it is transitioning in X/Y to different direction it shows up. Only in those 2 spots though. I'm not sure on the direction change as we usually climb mill.

Sounds like you have it narrowed down. As to the severity..
Any measurable egg-shaping when measured at 11 & 5?

Perhaps go old school and center your X&Y, drop your Z (put a long bar in a tool holder) then put an indicator on everything and see what moves when you manhandle each direction of both the table and the spindle. Thinking you will see either a measurably loose Z while flexing in the Y axis, or in the Y axis itself.
 
cut a 2 inch round boss and measure across the X axis , and directly in the Y axis. and report back. could be backlash. or you could have bad thrust bearing.
 
Sounds like someone needs a ball bar test

I know people see a ball bar test is the be all do all test. but I have seen them not tell the whole story. I recently was involved in a fadal that was adjusted , and calibrated by a ball bar. after the ball bar the machine would cut a egg shaped part had to cut a part ( the company that did the ball bar and came back, reran and said all is great) and put a actually load on it to find the problem and fix the machine. cut a part and put a load on the axis and spindle. that's truly the tell all and see all.
 
I know people see a ball bar test is the be all do all test. but I have seen them not tell the whole story. I recently was involved in a fadal that was adjusted , and calibrated by a ball bar. after the ball bar the machine would cut a egg shaped part had to cut a part ( the company that did the ball bar and came back, reran and said all is great) and put a actually load on it to find the problem and fix the machine. cut a part and put a load on the axis and spindle. that's truly the tell all and see all.

I agree, but a ball bar can have useful diagnostic info as well.
 
I know people see a ball bar test is the be all do all test. but I have seen them not tell the whole story. .
Ball bar test are by nature unloaded so can never tell the whole story or even half of it.
Servos, bearing and machine slides react differently when under pressure.
A very handy tool in the box but will not tell you the details when in a cut.
The old circle diamond square test from the early days of NC tells more but is so much more time consuming to do and analyze.
At around 10 and 4 o'clock things change a lot on who is the controlling axis as you are into the acc/dec that has to happen and both these ramps have to match.
A scope on both axis helps but that is also complicated. I'd chase trust bearings first and servo tune second.
Bob
 
We have a 2011 VF4 that seems to get a bit of chatter when we interpolate holes. It is always seems to show up at 11 o'clock and 5 o'clock if it was a watch face. Not sure if there are some parameters that will help minimize this? I assume there might be a bit of backlash when changing directions on either X or Y that might cause it? Its not horrible but it is there.

.
servo tuning needs to be done when servo keeps oscillating back and forth often for many seconds before hopefully stopping. many cnc have a servo diagnostic screen to see this. +/-1 might be .00004" and show up as .0001" TIR waves. +/-10 obviously is a much bigger problem. diagnostic screen will show if holding a steady 0 or if oscillating
.
when doing any straight or arc moves it can be oscillating back and forth too as it moves
 








 
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