Z axis has suddenly stopped going forwards <resloved>

[dmbgo]

Hi,
My Z axis is going in one direction only if I run a turning cycle. It takes the first cut, then instead of returning the Z axis to the beginning of the cut and moving the X axis in, it moves the X axis in, but reverses the Z axis for the amount of travel that it should be going forward for.
For example, if I try to turn 1mm off a 25mm bar in 0.1mm increments for a distance of 20mm, with the part co-ordinates starting at Z 20mm and X 25mm, it will do the following:
1/ Move X to 19.9mm and take a cut for 20mm. Reverse Z for 20mm
2/ Move X to 19.8mm and reverse Z for 20mm (now Z is 20mm away from the face of the job at +40mm.
3/ Move X to 19.7mm and reverse Z for 20mm (now Z is 40mm away from the face of the job at +60mm.

This repeats until the Z axis hits the home switch and the job is aborted.

Initially, I thought my Z axis was losing it's Dir signal from the controller, which would cause almost the same symptoms, but now I don't think so, when I use the MPG to move the Z axis, it consistently goes wherever I ask it, as many time as I like to spin the wheel on the MPG.

[dmbgo]

I had a cup of tea while I thought about this problem, and decided to run one of the standard programs that had not been changed by me. After my cuppa, I ran the Pawn gcode (metric version). I was just cutting air, but I wanted to see if it was caused by something I'd done.
Strangely enough the pawn gcode didn't work either, but it tripped the X axis limit switch.
The only other thing I've done recently, is to upgrade the CNC12 software from Ver4.5 to Ver4.62. I'm sure that everything worked after the upgrade, but to be certain, I'll uninstall V4.62 and reinstall V4.5 now. I think I can restore a backup created before the upgrade.

[dmbgo]

Well I uninstalled the latest 4.62 version of the Acorn software and reinstalled ver 4.5 and restored a report from just before I upgraded, when all was working. I then re-ran the pawn-mm demo file that comes with the software.

Sadly there was no change, the pawn-mm cnc file started to run, then the X limit was triggered shortly after the spindle started.
I'll give up on it for today, perhaps someone else may have some suggestions.

[Muzzer]

Are the feedrates in the file higher than the MPG feedrate? I could be that the g-code is asking for speeds that exceed the machine's ability.

But that doesn't explain the unidirectional behaviour. If this is a new development, is there a drag on the carriage in one direction? Has the carriage lock or the gibs become tight or does it need lubrication?

[martyscncgarage]

Well I uninstalled the latest 4.62 version of the Acorn software and reinstalled ver 4.5 and restored a report from just before I upgraded, when all was working. I then re-ran the pawn-mm demo file that comes with the software.

Sadly there was no change, the pawn-mm cnc file started to run, then the X limit was triggered shortly after the spindle started.
I'll give up on it for today, perhaps someone else may have some suggestions.

ALWAYS post a fresh report.
Did it actually hit the X axis limit? X+ or X-? Hard or soft limit?
Are you sure you set Part Zero correctly?

Marty

[cncsnw]

First, compare the machine's movements with what you see on the F8/Graph screen. That will tell you whether there is an issue with your CNC program or with the way the control is interpreting your CNC program.

Also, the F8/Graph screen will tell you whether running the loaded job would exceed your software travel limits (i.e. whether you are going to get something like "907 X axis travel exceeded, line 123").

Next, try writing and running a CNC program that moves Z in both directions, at a moderate feedrate. For example (assuming G21 metric setups)

Code: Select all

G1 G98 F500 W-20
W20
W-20
W20

If that moves in both directions without error, but the turning cycles (which always move Z- at feedrate, and Z+ at rapid) have a problem, then the issue probably relates to speed, not direction.

[dmbgo]

Are the feedrates in the file higher than the MPG feedrate? I could be that the g-code is asking for speeds that exceed the machine's ability.

But that doesn't explain the unidirectional behaviour. If this is a new development, is there a drag on the carriage in one direction? Has the carriage lock or the gibs become tight or does it need lubrication?

Hi Muzzer, I don't think there is a problem with the ways, no there is no more drag on the carriage in one direction than the other. The problem has also now swapped from the Z axis to the X axis, with the only pertinent change being the Gcode file that I was running. The machine happily moves in either direction, using the G0 command, so with my limited knowledge it should be trying to move as rapidly as it can.
I am using AC servo drives and motors, so there are no stepper stalls in play. I would assume (correct me if I'm wrong) that the servo controller would error if you asked it for an impossible speed, or the encoder indicated that it couldn't move for some reason.

[dmbgo]

Well I uninstalled the latest 4.62 version of the Acorn software and reinstalled ver 4.5 and restored a report from just before I upgraded, when all was working. I then re-ran the pawn-mm demo file that comes with the software.

Sadly there was no change, the pawn-mm cnc file started to run, then the X limit was triggered shortly after the spindle started.
I'll give up on it for today, perhaps someone else may have some suggestions.

ALWAYS post a fresh report.
Did it actually hit the X axis limit? X+ or X-? Hard or soft limit?
Are you sure you set Part Zero correctly?

Marty

Hi Marty,
Backup reports are attached, the most recent is the current configuration.
The limit hit was the X+ hard limit switch, which is an inductive proximity sensor. It was previously hitting the Z+ hard limit, which is the same type of sensor located on the tailstock base, so when the cross slide gets within 1mm of the tailstock, the limit is trigged. The Z limit is a moveable one, depending on the location of the tailstock.
I was very careful to set part zero, in both Z and X directions.

[dmbgo]

First, compare the machine's movements with what you see on the F8/Graph screen. That will tell you whether there is an issue with your CNC program or with the way the control is interpreting your CNC program.

Also, the F8/Graph screen will tell you whether running the loaded job would exceed your software travel limits (i.e. whether you are going to get something like "907 X axis travel exceeded, line 123").

Next, try writing and running a CNC program that moves Z in both directions, at a moderate feedrate. For example (assuming G21 metric setups)

Code: Select all

G1 G98 F500 W-20
W20
W-20
W20

If that moves in both directions without error, but the turning cycles (which always move Z- at feedrate, and Z+ at rapid) have a problem, then the issue probably relates to speed, not direction.

Thanks Cncsnw,
I was going to start running through the steps you suggested today, but 1st I thought I'd just run the same pawn-mm file that I ran yesterday. I got the same tripping of the X axis limit switch when running the file as yesterday. At least the lathe is consistent.
I then thought, what happens if I use the MDI to run the steps of the program manually? The only time that the X axis goes near the X limit is when it is commanded by the .cnc file to do a G28 move and when I did that manually through the MDI there were no errors and I was able to move to the other steps in the program with no errors as well.
I am starting to wonder if I have a compound error here. Perhaps my original issue was caused by my original program, and the subsequent tripping of the X axis limit, is for a different reason? Perhaps the limit switch (an inductive one) is tripping at different X axis points depending on the speed at which the axis is moving?
Is there some sort of change that I can make to the system where I specify a slightly larger distance from the home position for a G28 move, rather than the current position setting?

[cncsnw]

The end position for G28 moves is on the "Return Points" table: F1/Setup -> F1/Part -> F9/WCS -> F1/Return.

It is entered as machine coordinates (distance from machine home).