Reply with QuoteSounds mechanical. It could be that the Z axis ball screw drive pulley(s) or coupler is slipping on the ball screw or the motor.
Z-Zero shifting mid-process
I've run into an issue with the Laguna Swift and Richauto controller shifting the Z-Zero downwards mid-process.
The toolpath is a 3-pass roughing raster running top-to-bottom, stepping left-to-right in the pic, and should be cutting 1/4" each pass. The left most 'plateau' is referencing the original Z-zero and it ran fine. One what must have been the second pass and when I started watching the process again after leaving it on autopilot for the first pass, you can see that about a 1/3 of the way through the machine started stepping down - you can see each subsequent plateau before its started furrowing and stopped the process. I re-checked the Z and found it to be 165 units lower that the original Z-zero level.
I think these resets were happening when the spindle returned to the X-Zero and began its next run down the - it doesn't look like there were any resets along the X-axis once it began the run.
This is new behavior for this machine. It occurred on the next previous job - ruined the blank - and I set that one aside for the current job and have the same behavior.
The bit isn't slipping in the collet, I double-checked the Z-zero before I started.
Has anyone seen this thing before? It feels like an issue with the hardware - the spindle is slipping down?
Thanks in advance for your help.
Similar Threads:
Re: Z-Zero shifting mid-process
Sounds mechanical. It could be that the Z axis ball screw drive pulley(s) or coupler is slipping on the ball screw or the motor.
Jim Dawson
Sandy, Oregon, USA
Seems to occur only on longer duration tool paths, 2+ hours.Originally Posted by Jim Dawson
Also, I recently refreshed my lube reservoir with 10W-30 oil based on incorrect information and have since learned that SAE 30 is the correct viscosity. I was getting unusual excess oil drippings from under the spindle assembly and I wonder if this is related to the slipping. My plan is to flush out the oil lines with SAE 30, clean-up the assembly, refresh the coolant and try again. I don’t know whether thinner oil at higher temps could be causing this, but that’s viscosity change is a variable co-incident with the slipping.
Re: Z-Zero shifting mid-process
I think it is unlikely that 10-30 vs. 30wt oil would make the difference.
Jim Dawson
Sandy, Oregon, USA
Re: Z-Zero shifting mid-process
I think you're basically correct.
Per Laguna, it's likely to be a lubrication issue at the ball screw bearing set owing to the relatively short up/down Z-travel on this job - probably less that an inch per tool path. They recommend cleaning the ball screw, lubricating the bearing set with white lithium grease and pausing small hot zone tool paths after a couple of hours to manually re-lube the bearings and hot zone. The slip packs that route oil from the reservoir that area sometimes can't maintain adequate lubrication to short travel hot zones on lengthy tool runs according to the tech - problem more common on their lighter duty IQ series but also the likely culprit on my Swift.
So, I'll clean it up, re-home, manually spray lube the bearings at the start, pause after 90 minutes or so to hit it again, and see what happens.
Re: Z-Zero shifting mid-process
That's crazy. Sounds like a design flaw, never heard of anything like that before. Maybe clean and lube the rails also.
Jim Dawson
Sandy, Oregon, USA
If manually lubricating the ball screw at the bearing nut solves the problem then I’ll need to figure out why the bearing pack is starved for lubricant. It does not seek to me that should be happening. Perhaps the line or one or more ports is clogged. But for now, manual lube seems like a good way to narrow down the cause.
Re: Z-Zero shifting mid-process
This issue remains unresolved. I applied Laguna's advice and lubricated the ball screw manually at the bearing nut during the course of a short tool path. No change in the failure case – the spindle is not correctly maintaining Z-zero.
The Z-zero in the program is at the top of the material and set to the zero reference with the touch-off puck at the start of the run. It visibly reset three times during the course of a 3 pass roughing run by ~ 1.5mm each time. At the conclusion of the run, I checked the Z-zero and found that per the controller it was 4.5mm lower than the original Z-zero set at the start of the run by the touch-off puck and visually confirmed before the run started.
You can see the effect in the pic - the last 1.5 mm step down near the top.
I don’t think this is a lubrication issue alone – the ball screw bearing nut is well lubricated. The machine was re-homed before the tool path was loaded and run; this is the 3rd consecutive roughing pass with this issue. A pocketing pass completed prior to the roughing pass was flawless. The lubrication might improved the situation, however, prior to lubing the situation looked like this:
So it seems like something is binding on the Z-up - the spindle isn't actually going up and the cumulative loss of altitude was 4.5 mm over the course of the tool path.
Last edited by MillAlien; 01-27-2021 at 06:45 PM.
Re: Z-Zero shifting mid-process
I've discovered that the step-losses are occurring in exactly the same locations on the pass: I ran the first roughing pass and stopped the process on trial #1. Put in a new blank. Ran the pass again and compared trial #1 to trial #2. Its a ditto.
I did the same thing with a completely different 3D model. Same result. The error on trial #1 lines up with the error on trail #2. Using the same post-processed MMG file.
What does this suggest?
Re: Z-Zero shifting mid-process
Mechanical issue
Gerry
UCCNC 2017 Screenset
[URL]http://www.thecncwoodworker.com/2017.html[/URL]
Mach3 2010 Screenset
[URL]http://www.thecncwoodworker.com/2010.html[/URL]
JointCAM - CNC Dovetails & Box Joints
[URL]http://www.g-forcecnc.com/jointcam.html[/URL]
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
Re: Z-Zero shifting mid-process
To be clear, the error replicates in the same X-Y-Z location on each trial model, not the same X-Y-Z location on the machine bed. If I didn't know anything else, I'd think software error in the tool path instructions.
If mechanical, what might it be? All the axes are aligned, spindle is working fine, and this issue occurs only on 3D roughing passes.
Re: Z-Zero shifting mid-process
What software are you using?
I doubt it's a software issue, though, as I've never seen anything like that happen due to software. It would more likely be due to the machine controller than software, but again, I've never seen anything like that,
Can you post the g-code so we can check it? If the g-code is fine, then it's something in your machine causing it.
Gerry
UCCNC 2017 Screenset
[URL]http://www.thecncwoodworker.com/2017.html[/URL]
Mach3 2010 Screenset
[URL]http://www.thecncwoodworker.com/2010.html[/URL]
JointCAM - CNC Dovetails & Box Joints
[URL]http://www.g-forcecnc.com/jointcam.html[/URL]
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
Re: Z-Zero shifting mid-process
That's a new bit of information. If it's not happening at the same place on the table then it could be a software/G code issue. This does not rule out mechanical where a commanded rapid direction change or something could be occurring and causing something to slip.
Once this error occurs, does the position recover on later moves? Or does the ''new'' position maintain through the rest of the part?
I have seen math errors occur in the machine software especially on G18 (XZ), and G19 (YZ) arc moves. This is unusual but not unheard of, and 3D roughing passes are especially complex.
Jim Dawson
Sandy, Oregon, USA
Re: Z-Zero shifting mid-process
The new position is maintained.
I've replicated this five times now; same step error in the tool path at the same coordinate position relative to the work-piece itself, not the table.
As part of my trial & error approach to figuring this out, I re-calc'd a new roughing path using the manufacturer's tool library parameters for the tool I'd been roughing with (Amana 46426). The calc'd result was a single-pass instead of the 3-pass path I'd been running with the error results. I ran that MMG. Perfect. No errors - no errant step-downs.
These are the Amana parameters, per their tool library:
When these shenanigans began and with the same tool, I'd edited the parameters trying to perfect my chip-load:
Its with those user defined parameters that I get the 3-pass roughing path that's got the errant Z-step downs that I've been describing.
I think I never ran into this before because I only recently started messing around with tool parameters - up until about three weeks ago I used the Amana library parameters and never gave it a second thought. I didn't even know what "chip load" meant until about three weeks ago when I decided to up my game.
Again, I just don't understand enough about this technology to really figure out what's going on, but my intuitive thinking is that I could replace/adjust stepper motors and ball screws until the cows come home without solving the problem. Whether its controller related, a post-processor problem or a VCarve problem is what I'm having a hard time sussing out. But at this point I'm pretty sure I could re-run the jobs with unadulterated tool definitions that have been screwed up in the past two weeks with adulterated definitions and I bet they'd come out fine.
Re: Z-Zero shifting mid-process
Also, I've been watching the path carefully and there really isn't any rapid direction change when the spindle suddenly dives about 1.5mm - its rastering along the X-axis smoothly with not a whole lot of Z motion when it looses altitude. I freely admit my ignorance, but this really seems like the head-end is telling the steppers to do something they're just following instructions.
Re: Z-Zero shifting mid-process
Given that a tool path change fixed the problem, I would no longer say it's mechanical.
Now it's time to do some experimenting and see what parameter changes have that effect.
Jim Dawson
Sandy, Oregon, USA
Re: Z-Zero shifting mid-process
Have you tried to look at the gcode in a simulator? That would save some time and materials. It would also help identify if it's in the machine or the post processor.
I also noticed in the pictures you posted that the feed rate changed between inches per min and inches per second. Is the machine really moving that much faster or slower?
VCarve’s preview looks like a simulation but I don’t think it actually tracks the g-code for the machine itself. For the multi-pass path, the simulation and the actual tool movement aren’t the same. They’re close, but not the same.
As for IPM v IPS. I’d set the IPM in my edited parameters based on the chip load formula. The 3-pass path runs for 60 minutes w about 20 minutes per pass and the single pass path is about 30 minutes. The IPS is Amanda’s unedited parameter from there tool library.
I sent the parameter information to Laguna and they recommend lowering the plunge rate to 30 IPM. The tech noted that “ Plunging at the higher speeds will cause over shoot and possible lock-ups in Z. Tooling Manufacturers suggestions seldom work for all machinery, and are often way too aggressive.”
So, as Jim suggests, back the drawing board. But at least it seems that I’ve narrowed this down to a tool parameter/pathing problem rather than a mechanical issue.
Re: Z-Zero shifting mid-process
Sorry, I was referring to a 3rd party Gcode viewer. A couple of examples are ncviewer or CAMotics. I have not used them because all my CNC controllers have a preview of the Gcode. In your case I think looking outside the software is a good thing.
I am confused on the speeds you show. One setup has it going 200 inches per minute and the other has it trying to do 150 inches per second. 150 inches per second is 9000 inches per minute! That would put the machine constantly trying to go as fast as it can. Bouncing on the limiters could have interesting problems.
Re: Z-Zero shifting mid-process
Yes, the speeds are confusing - I mis-clicked on that drop box at some point but have fixed it and it's not solved the step-down problem.
Moving on...
I loaded and ran the .mmg file in CAMotics and I do NOT see the step-downs in the simulation.
So what I know so far is that:
1. The only toolpaths with errors are multi-pass roughing passes - I've run single pass roughing and finish (e.g., single-pass) 2.5D tool paths with no problems, yet multi-pass roughing passes always have errant step downs.
2. The errant stepdowns always occur in exactly the same coordinate position relative to the workpeice's XYZ-0 origin for every toolpath. I ran one toolpath four times - the step downs are in the same places on each; I ran another toolpath from a different model twice and again, the errant stepdowns are the same on both of those; I ran a third toolpath .. ditto.
3. Changes in tool parameters change path times, cut quality & etc., but never resolve the errant step downs unless the pass depth is set such that there is no second (or third) pass.
These seem to me to rule out mechanical issues on the machine itself. It seems like the steppers are just following orders.
4. The VCarve post-processed gcode appears to be error free on the CAMnotics simulation, which I think would rule out a post-processor issue in VCarve.
So what's left? Doesn't this point to a controller system failure? What's done about that sort of thing? Firmware re-install? Are there boards or some other quasi-consumables that could have failed?
