Z axis problem

[dakotablue]

OK, I have progressed to a test cut on my machine. I created a simple test toolpath consisting of a rectangular groove 10 x 12 x .250 deep. The x and y are exactly correct but the z is cutting at . 167 deep instead of .250. I calibrated the motors using the wizards. Thanks in advance...

 

[cncnutz]

Hi dakotablue

Three possibilities spring to mind.

You lost steps while decending to the required cut depth, the Z axis was not zeroed correctly to the material surface or the calibration was not successful. Without more testing you will not be able to narrow down the problem.

How did you Zero the cutter to the surface of the material? Manually or using the probing routine?

Here is how I would test to see where the problem is located.

• Rerun the test cut and after zeroing the Z axis check that an MDI command of G0 Z0 sits the cutter on the material surface. (This tests the Axis Zero process)
  
• I would then run the cut file and then go back to MDI and do the G0 Z0 again. Check to see if the cutter still sits on the material surface. (This checks for lost steps in the Z axis)
  
• Measure the depth of cut (This tells you if the calibration was correct)
  

Once you know where it is wrong we can look at finding a solution.

Cheers Peter

 

[dakotablue]

Hey again, Peter.

Here is what I did. I homed the machine and jogged the cutter to the center of the work piece. I zeroed using a sheet of paper. Reset all the axis to 0. Jogged the cutter up, entered into mdi g0z0, cutter went back to the paper. Then I jogged the z up to clear the material and ran the toolpath. Same result. Checked the depth of cut still shallow at .167. Jogged cutter up, entered into mdi g0z0. Cutter came back to the paper at perfect 0. Hope this makes sense. Gary

 

[cncnutz]

Hi dakotablue

That is excellent. From the results we now know that the axis was zeroed correctly before the cut started and because the Z axis returned to the original Z position after the cut you did not loose steps.

The only reasonable explanation is the z axis is not calibrated correctly. When you ask it to move 0.25" it moves only 0.167"

You can test this by measuring a piece of material eg 0.75" then put the cutter on the table surface and zero the Z axis. Next go to MDI and enter G0 Z0.75 (or what ever the material thickness is)

The cutter should now move up to the height of the material but I think you will find it is will only move a bit over half the height of the material.

Cheers Peter

 

[breezy]

Gary,

Checked the depth of cut still shallow at .167. Jogged cutter up, entered into mdi g0z0. Cutter came back to the paper at perfect 0.

This is pointing to incorrect calibration. Use a block of known dimensions and zero to the top of it, then remove it, issue a MDI command to move the distance of that dimension, you should touch the baseboard/bed. Use this method to calibrate the Z axis with the wizard.

Regards,

Arie.

Edit: Peter was replying at the same time as I was, but I was delayed in sending it.

 

[dakotablue]

OK, I zeroed to the top of a 1 2 3 block. Reset all axis, entered g0z-25.4. Cutter tried to jam through the machine surface. So what do I do now?

 

[dakotablue]

Sorry, my bad. We're in inches here?? Did it again and the cutter is shy of bed.

 

[dakotablue]

Cutter was . 323 off surface

 

[evermech]

I'm liking peters method of checking the Z axis better as it moves the tool away from the machine bed so no crashing involved.

you will need to post details of the Z axis drive setup and mechanical properties in order to determine what is going wrong with the calibration.

Guy

 

[dakotablue]

Something is definitely wrong. I go through the wizard using a 1" block and enter the info but when I g0z-25.4 cutter never makes it to the table. I'll try to upload the z info.

 

[dakotablue]

Thanks to everyone. I rebooted masso and went through the wizard process again and my cut was at . 24.99. That's close enough for me. Gary

 

[breezy]

Guy,

I'm liking peters method of checking the Z axis better as it moves the tool away from the machine bed so no crashing involved.

Gary had reported that he was coming up short on a negative movement, so I assumed that moving in that direction would be safe and allow him to measure the distance he was short to adjust his calibration. But Peter's method is safer.

Gary,

went through the wizard process again and my cut was at . 24.99.

Now you can fine tune your calibration by changing the last digit of the wizard's result, as you are still coming up short reduce the digit by one and repeat until you are spot on.

Regards,

Arie.