cut quality issue/troubleshooting

[indredcold]

Just finished my first cnc router, I am getting bad cut quality on curves and holes, ie bumpy curves/irregularly shaped holes. I am not sure what might be causing the issue....

Machine specs are

5x10 welded steel base
Aluminum gantry
DMM 750w servos all axes/DMM BoB
Mach4, Mach 2/3 ARC post processing
Cheap 2.2kw Huanyang spindle (for now)
Hiwin rails
Avid CNC rack and pinion drive system

I have lowered feedrate to lowest setting, seems to help slightly but problem still exists, checked for loose bolts etc.
Also calibrated axis movement...I get repeatable movements within .003. Is this still too high?
Only thing I can think of is my calibration is off?

Any help appreciated!

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[wendtmk]

Some pictures of the cut issues you are having would be a big help.

Mark

[Vlod]

Try different computer, may be it’s not machine issues and it could be not sufficient power, though irregular shape holes usually if the machine is not stiff enough, to much stick out cutter, z axis is extending to much…

[awerby]

Is it noticeably shuddering when the machine is cutting? Sometimes that's due to being in "exact stop" mode rather than "continuous contouring" - the machine stops at every listed coordinate, rather than cruising smoothly through them.

Another thing to check is deflection of the Z axis. Put a dial indicator on it and push gently on the spindle when it's at full extension. If you get significant motion - more than a millimeter or so - that lack of rigidity could be causing the tool to shudder as it attacks the material.

[LangleyWoodworker]

Check if both of your Y axis are being driven. I had the same issue before - weird cuts and irregular holes, and then realised that one of the Y axis wasn't being driven as it was hooked up in reverse and the drive was throwing and error and disconnecting the motor. Ended up having to remove the belt to identify the issue. But you should also be able to tell by trying to manually move each side of the gantry

[indredcold]

Thanks for all of your suggestions! Still having problems..

I am running in continuous contouring
Checked Z deflection...rock solid, however, with motors powered on, I am seeing about .020- .030 deflection in both the x and y axes, ugh. (Checked for slop in the drive belts, but it appears to be the motor shaft is moving)
Both slaved Y motors are working properly.
I am using vcarve and did switch from Mach 2/3 ARC post processing to the Avid CNC post processor and did seem to get a little better cut. (wishful thinking probably)

Given the deflection of the x and y, would this carry over while running?

[Vlod]

It looks like its overshooting. Have you try to lower acceleration not the speed in mach3 motor tuning.

[boydage]

Have you checked your backlash?

Sent from my SM-S908E using Tapatalk

[TMToronto]

I believe the Avid pulleys are keyed but in case your DMM shafts are not perhaps double check set screws and tighten motor shaft connections.
Also, are you seeing this issue with larger diameter circles, and direction changes with less extreme angles (> 90/square corners)?

[joeavaerage]

Hi,

It looks like its overshooting. Have you try to lower acceleration not the speed in mach3 motor tuning.

I would go the other way, have the higest acceleration your steppers will tolerate without missing steps. I would lower the velocity.

The faster a machine can accelerate the better its toolpath following. In the case pictured the machine needs to slow to a stop, or near stopin the X direction, and then accelerate away at 90⁰.
The higher the acceleration the faster and better that can happen. If you slow the velocity of the axis as it approaches the corner that to will save the deviation.

Could this be caused by the gantry flexing? If the machine is cutting the cutting forces will deflect the gantry to a certain extent. When the cutting forces reduce as the axis slows the flex
of the gantry will 'spring back' causing the defects you are seeing. Try the same toolpath but with just the very very l9ightest of cuts.....does it change? If it does then flexure of your machine
may be the culprit.

Craig

[mactec54]

Thanks for all of your suggestions! Still having problems..

I am running in continuous contouring
Checked Z deflection...rock solid, however, with motors powered on, I am seeing about .020- .030 deflection in both the x and y axes, ugh. (Checked for slop in the drive belts, but it appears to be the motor shaft is moving)
Both slaved Y motors are working properly.
I am using vcarve and did switch from Mach 2/3 ARC post processing to the Avid CNC post processor and did seem to get a little better cut. (wishful thinking probably)

Given the deflection of the x and y, would this carry over while running?

Yes, if you have that much deflection that will cause you a lot of problems, what settings have you used in the servo drives

Did you use a key in the motor shafts