Chatter During Cutting
Chatter During Cutting
Chatter is a resonant phenomenon where the machine or workpiece vibrate. This directly affects the look and the quality of your final cut making it look “not straight”, it gives it a look of waving or squiggly lines. In order to solve this issue there’s a couple of things that can be looked at:
Mechanical:
Servo motor checking
Once your machine is on and Homed, the servo motors activate making them so that the only way for your to move them it’s through jogging them with the control panel. If the servo motors are not “solid” this can cause chatter on your cuts. Because of this, one of the first things you should do when dealing with chatter is check your servo motors to make sure that everything is engage correctly, we do this by “checking for play”. To check for play on your machine servo motors follow these steps:
1) Turn Machine on and Home completely.
2) Jog the Y axis close to the center of the CNC table.
3) Physically go to one of the sides of the Y axis and grab with both hands as we move it back and forth.
4) Move on to the opposite side of the Y axis repeat
Since the motors engage after homing, it should be nearly impossible to move any of the axes by hand. If during the testing you feel movements, this is called play and in most cases, can be solve easily. Having play means the gear on the servo motor is not sitting tight against the gear on the machine’s track. By loosening up the bolts that hold the servo motor we can re-sit the motor back on the track. The bolts should be retightened as the servo motor is being held up against the helical gear track with pressure. If your machine has a tightening belt rather than the motor sitting directly on track move the servo motor away from the track as to tighten up the belt that is attached to the pinion on the machine’s track.
Workpiece:
If we are sure all of our mechanical is good then we can move into our workpiece. Most of the times we can get a “squiggly” line rather than a straight line on our cuts if our workpiece moves as the CNC is machining it. Moving parts can be handle in different ways but the first thing we should do is to make sure our vacuum system is working correctly. These are some of the things we can check for when it comes to the Vacuum system:
● Has the Spoil board been “Fly Cut” on both sides?
● Use MDF (Medium Density Fiber) and not HDF or LDF
● Check Vacuum Filters
● Check Vacuum oil or grease levels
● Check vacuum hoses and piping for tears, holes, kinks or vacuum leaks
● Check for current vacuum hold down reading.
If everything looks good on the vacuum system and mechanical but still have chatter proceed to servo pack settings
Servo Pack Settings:
Depending on the customer’s applications and the materials they are working with sometimes the servo drivers will
need to be adjusted to handle those applications and materials correctly. Chatter can sometimes also happen when the
settings on our servo motors for acceleration and deceleration are not set for softer or harder materials.
On our X, Y1 and Y2 Delta servo drivers these settings are under P2-00 and P2-04, by default these are set to 40 (P2-
00) and 1,000 (P2-04) and they should be increase or decrease proportionally, and their ratio is 1:5.
Spindle R.P.M.:
Since chatter is a resonant phenomenon that is excited by the tool flutes striking the workpiece, it only makes sense
that certain spindle speeds will beat on the workpiece at exactly the right frequency to maximize chatter.
In order to minimize chatter, you need to find out which frequencies to avoid, or we can reverse that problem and look
for frequencies where you can push hard without exciting chatter. This is why slowing down may work, but speeding up
may work just as well or even better. When chatter hits, play with your spindle RPM's a bit to see whether you can
make it stop. Try increasing the speed first, and then try slowing down. It may be that just twisting the knob solves your
problem.
Rev. 8112017
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