X2 z-axis drifting.

A

Andros

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My cnc converted x2's z-axis is drifting. When i cut mdf it appears fine but when i cut steel with carbide endmills an very light cuts (0.2mm deep, 150mm per min feedrate), its not cutting derp enough and pencil finish its cutting too deep.

The couplings are tight. Velocity is low (1000 mm p minute) and acceleration is set to very smooth.

X and y are perfect.

Any ideas?


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Andros said:
My cnc converted x2's

z-axis is drifting.

When i cut mdf it appears fine but

when i cut steel with carbide endmills an very light cuts (0.2mm deep, 150mm per min feedrate), its not cutting deep enough and

pencil finish its cutting too deep.

The couplings are tight. Velocity is low (1000 mm p minute) and acceleration is set to very smooth.

X and y are perfect.

Any ideas?
Click to expand...

I take it you're just getting this set up?

What do you mean by drifting? Z going up as it mills? Does the screen show a different height when it moves?

Are you using stepper or servo motors?

Same type of motors on each axis?

What is a "pencil finish "?
 
Yes. Recently build it but im now putting it through the paces.

Nema23 steppers. Geckodrive. Mach3. 48v. X and y motors are the same 270oz 2.8a. Z is a 425oz 2.8a.

First pass. Stock is 3.0mm but set the stock in meshcam to 3.1 but it barely cut throgh the stock.

Then for the chamfering pass it it was set to dig 1.2mm into the stock but instead dug 2mm in.

Weird? Loosing steps?




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Using cncfusion with ballscrews and some backlash compensation.


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Andros said:
Yes. Recently build it but im now putting it through the paces.

Nema23 steppers. Geckodrive. Mach3. 48v.

X and y motors are the same 270oz 2.8a.

Z is a 425oz 2.8a.

First pass. Stock is 3.0mm but set the stock in meshcam to 3.1 but it barely cut throgh the stock.

Then for the chamfering pass it it was set to dig 1.2mm into the stock but instead dug 2mm in.

Weird?

Loosing steps?
Click to expand...

Stepper motors will loose steps and the controller will not know about it if there is any binding.

I'd turn the power off and check for any binding in the Z. Turn the motor with your hand the full motion.

Without material, can you have the Z go down and then back up to the same point? How about it going down a certain depth and then measure the depth.
 
Thank you! Ill give it a shot tomorrow and let you know the outcome!


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My guess is loosing steps and the source is the ball screw coupler. Mark the screw, coupler, and motor and make some slow jogs with no load and then the same motions in material where you noticed the irregular cut. Id drill and tap for more set screws and grind/file a flat on your stepper or screw if you need too.
 
If you are running mach3, don't forget you need to tune the number of steps per unit on the mill. If you don't do this it will appear that you are losing steps over longer distances due to the incorrect number of steps needed to move any distance. Hoss2006 at CNCZone has a video showing how to do this, watch this:

http://www.youtube.com/watch?v=XkO5tc-jSxw

-Freeman

PS - this needs to be done for each axis.
 
Last edited:
Having your steppers set for smooth speed and acceleration doesn't necessarily mean that they are at their best setting. I was having trouble when I first got my X2 up and running. I had set the motors for the smoothest operation before they were mounted. Steve (jumps4) had me slow them down quite a bit. That improved things a lot.

Later, when I was actually trying to make something, my Y-axis was losing about 3/8" (10 mm) on the return run. I slowed the motors a bit more and it got much more accurate.
 
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