Z Axis Plunging too Deep into part < part zero, tool offsets, turns ratio >

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Nigelo
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E415F6F70BC3-0318203049
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Re: Z Axis Plunging too Deep into part

Post by Nigelo »

Using Z home as your Z ref is only as good as the REPEATABILITY of your home switch. This also assumes that your Z axis is accurately calibrated of course and that EMI is not inadvertently interfering with movement.

FWIW, I have to use Z home as Z ref on my Router as I do not have fixed tool holders for that machine. I was using a Z ref tool on my Mill (with fixed tool holders) but after successfully using swissi's ProbeApp on the router, decided to check out the repeatability of my Z home. As the ProbeApp has this repeatability check built in, my results showed repeatability within 0.0002" or roughly 8 microns. It was therefore a no-brainer to use Z home as Z ref on my Mill as this frees up the previous Z ref toolholder.

Long story short, check your Z home repeatability AND your Z calibration. Also consider getting yourself a corner plate tool checker and / or Probe and then swissi's ProbeApp

hope this helps
martyscncgarage
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Location: Mesa, AZ

Re: Z Axis Plunging too Deep into part

Post by martyscncgarage »

Home your machine and pay attention to the movement. It trips the switch and backs off a predetermined amount and sets home at that position. Look at machine coordinate Alt d (to toggle it, it can also be turned on in CNC preferences)
It is NOT going back to trip the switch. The control knows where the home position is after it has been homed.

Marty
Reminder, for support please follow this post: viewtopic.php?f=20&t=383
We can't "SEE" what you see...
Mesa, AZ
martyscncgarage
Posts: 7490
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Location: Mesa, AZ

Re: Z Axis Plunging too Deep into part

Post by martyscncgarage »

Nigelo wrote: Wed Jan 06, 2021 9:04 am Using Z home as your Z ref is only as good as the REPEATABILITY of your home switch. This also assumes that your Z axis is accurately calibrated of course and that EMI is not inadvertently interfering with movement.

FWIW, I have to use Z home as Z ref on my Router as I do not have fixed tool holders for that machine. I was using a Z ref tool on my Mill (with fixed tool holders) but after successfully using swissi's ProbeApp on the router, decided to check out the repeatability of my Z home. As the ProbeApp has this repeatability check built in, my results showed repeatability within 0.0002" or roughly 8 microns. It was therefore a no-brainer to use Z home as Z ref on my Mill as this frees up the previous Z ref toolholder.

Long story short, check your Z home repeatability AND your Z calibration. Also consider getting yourself a corner plate tool checker and / or Probe and then swissi's ProbeApp

hope this helps
Nigelo,
True statement, but milling is struggling with the tool setup concept.
Let's get him through one way and then the other way. (Both explained in Centroid's mill training videos)

Bottom line
Without a properly set up machine which is the first priority, he'll be chasing his tail with much frustration.
With his turns ratios the way they are, I am not completely convinced the machine is setup correctly.
And how he is verifying the machine axis calibration and test for backlash and it would be good if we could "See" how he is verifying that.
I posted two Centroid Documents on Coarse and Fine setting of the DROs.

Marty
Reminder, for support please follow this post: viewtopic.php?f=20&t=383
We can't "SEE" what you see...
Mesa, AZ
milling
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Re: Z Axis Plunging too Deep into part

Post by milling »

I did go through the documents for coarse and fine adjustment and backlash and believe i did it right. Also, when I command a move on any of the axis the dro will match the physical movement on the machine

Is there a way I can do another check on the z axis home switch-when i click the reset home button it definitely hits the switch and then backs off just slightly. I think when reset home switch is selected the axis will move until it actually hits a switch.

When a program is run i think its looking for a actual distance number for home and not a switch
martyscncgarage
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Location: Mesa, AZ

Re: Z Axis Plunging too Deep into part

Post by martyscncgarage »

milling wrote: Wed Jan 06, 2021 10:54 am I did go through the documents for coarse and fine adjustment and backlash and believe i did it right. Also, when I command a move on any of the axis the dro will match the physical movement on the machine

Is there a way I can do another check on the z axis home switch-when i click the reset home button it definitely hits the switch and then backs off just slightly. I think when reset home switch is selected the axis will move until it actually hits a switch.

When a program is run i think its looking for a actual distance number for home and not a switch
Centroid controls, when they home, the hit the switch and back off a predetermined amount THEN set home at that point.
Once the machine is homed (MACHINE HOME) everything references from that point.

You need to dig in and give things a try. It seems you keep questioning things. No better tool to learn than to dig in and try things out.
Download the CNC Mill Operator's Manual and read it. Try the Intercon Excercises. Doing will help you understand.

Learn to use the space bar on the keyboard to do a feed hold. To resume press Cycle start. All covered in the Mill Operators manual.

Good luck!
Marty
Reminder, for support please follow this post: viewtopic.php?f=20&t=383
We can't "SEE" what you see...
Mesa, AZ
milling
Posts: 58
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Re: Z Axis Plunging too Deep into part

Post by milling »

Thanks Marty- why do you say to use the spacebar for feedhold? Is clicking feedhold in the vp not a good way to do this? I can do that I just want to make sure Im not doing anything wrong.

I actually printed out the entire manual. The thing that bothers me is it really is not up to date with the currect software I have. There are things in the manual that do not sync up with what I have- such as being able to import .dxf files, also some of the paramters do not line up either. The manual I printed is CNC12 Version 4.14 and I think the software is 4.59. Hopefully I downloaded and printed the correct manual!
martyscncgarage
Posts: 7490
Joined: Tue Mar 28, 2017 12:01 pm
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Location: Mesa, AZ

Re: Z Axis Plunging too Deep into part

Post by martyscncgarage »

milling wrote: Wed Jan 06, 2021 12:11 pm Thanks Marty- why do you say to use the spacebar for feedhold? Is clicking feedhold in the vp not a good way to do this? I can do that I just want to make sure Im not doing anything wrong.

I actually printed out the entire manual. The thing that bothers me is it really is not up to date with the currect software I have. There are things in the manual that do not sync up with what I have- such as being able to import .dxf files, also some of the paramters do not line up either. The manual I printed is CNC12 Version 4.14 and I think the software is 4.59. Hopefully I downloaded and printed the correct manual!
The space bar on the keyboard does feed hold. Yes VCP can do it to. Its easier to hit the space bar. Wireless MPG also has it, it works too

You can NOT import DXF files. You will have to run your DXF files through a CAM software package like Sheetcam, CAMBAM or similar.
Centroid IS discussing bringing back .dxf import.

The only manual we have right now is 4.14. It was directed at Servo version but the software is VERY similar. WHICH parameters are not the same?
You have to dig in and try the software and learn. We can try and fill in gaps, but we can't do it for you.

Marty
Reminder, for support please follow this post: viewtopic.php?f=20&t=383
We can't "SEE" what you see...
Mesa, AZ
cncsnw
Posts: 1874
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Re: Z Axis Plunging too Deep into part

Post by cncsnw »

A "reset home" key is going to move to do the same thing that power-up homing does: move to find the switch, back off, and then set machine zero there.

For testing purposes, you really want to do the moves that find the switch and back off, without resetting machine zero. That way you can the difference from one attempt to the next.

You can do that with "M92/Z".

To test the repeatability of your home switch:
1) Power up and home the machine.
2) Press Alt-D to switch the DRO to display machine coordinates
3) Press F3/MDI
4) Jog down (in slow, continuous mode) about 1/4"
5) Enter "M92/Z" and press Cycle Start
6) When it comes to a stop, write down the Z value from the DRO
7) Repeat steps 4-6 half a dozen times.

While you are at it, with the Z at its homed position, mark the orientation of the motor shaft and ballscrew, so you can tell in the future whether they are rotated back to this same orientation.

Next time you run a job, and see that Z is going to go too deep by a large amount (0.2" or more), then:
1) Press Alt-D to switch to machine coordinates
2) Press Tool Check to move the Z to where it thinks the homed position should be
3) Verify that the Z DRO reads 0.0000 in machine coordinates.
4) Check your motor and screw orientation marks to see whether it is really there
5) Press F3/MDI
6) Enter "M92/Z" and press Cycle Start
7) When it comes to a stop, write down the Z value from the DRO.
8) Also at that point, re-check your motor and screw orientation marks.

If the result from step (7) is significantly outside the range that you saw on the previous set of tests, and step (8) shows the orientation marks do not line up, then you have mechanical slippage.

If the result from step (7) is significantly outside the range that you saw on the previous set of tests, and step (8) shows that the motor shaft and ballscrew are back where they should be when at home, then you have lost position due to dropped steps or bogus steps.
milling
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Re: Z Axis Plunging too Deep into part

Post by milling »

Thanks cncsnw- Ill give it a try
milling
Posts: 58
Joined: Mon Dec 14, 2020 5:41 pm
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Re: Z Axis Plunging too Deep into part

Post by milling »

Thanks everyone for the help. It seems to work now. I have found that when I am in a program you cannot switch to another program without having the issue I was having. Not sure if that sounds right but thats whats happening. If I want to run a new program, i shutdown CNC12 and then pick the program I want and it seems to run right. I think each program retains the WCS zero position that was set for that particular part.

Anyway thanks again everyone and Im going to keep trying to run new programs to make sure the issue does not re-appear.
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