Z-Zero shifting mid-process

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MillAlien
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Z-Zero shifting mid-process

Post by MillAlien »

I've run into an issue with the Laguna Swift and Richauto controller shifting the Z-Zero downwards mid-process.
IMG_7407.jpg
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.

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TReischl
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Re: Z-Zero shifting mid-process

Post by TReischl »

Yup, lots of other folks have seen this sort of thing.

Check the easiest things first, like the plunge feedrate you are using. Most "end mills" do not like plunging because most are not true end cutting end mills.

Look at the mechanical connections, but honestly, that does not strike me as the issue.

Years ago I had something similar, turned out that the stepper driver boards were not being cooled enough.

What you can rest assured it is not is the software, otherwise we would all be on here complaining to high heaven.
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MillAlien
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Re: Z-Zero shifting mid-process

Post by MillAlien »

TReischl wrote:
Thu Jan 21, 2021 1:28 am
Yup, lots of other folks have seen this sort of thing.

Check the easiest things first, like the plunge feedrate you are using. Most "end mills" do not like plunging because most are not true end cutting end mills.

Look at the mechanical connections, but honestly, that does not strike me as the issue.

Years ago I had something similar, turned out that the stepper driver boards were not being cooled enough.

What you can rest assured it is not is the software, otherwise we would all be on here complaining to high heaven.
This particular toolpath is using a 1/4" ball-end. I set the feed and speed to optimize the chip load at .010 and it was running real well on the first pass at 200 IPM with a plunge of 100 IPM and a .25 pass depth with 10% stepover. The VCarve simulation runs fine - does exactly that I expect, without the unexplained stepping down that's happening in the real world.

I'll open up the cabinet tomorrow and make sure there's nothing funky going on in there, but the muffin fans are operating normally. I'll also check the snug on the spindle bracket or whatever the hell holds the spindle to the machine. To be honest, I'm a terrible mechanic and have been wary of every having to turn a screw on that thing from the day I bought it.

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Re: Z-Zero shifting mid-process

Post by gkas »

Are you performing daily/weekly/monthly maintenance on it? Lube, adjust, clean?

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Re: Z-Zero shifting mid-process

Post by Rcnewcomb »

o be honest, I'm a terrible mechanic and have been wary of every having to turn a screw on that thing from the day I bought it.
You have a good machine and you will actually be more comfortable with it when you get to know more about it -- I know I have with my machine.

The very nature of CNC means there is vibration, so things occasionally come loose. A clamp, wire, or screw may have come loose. It is an easy fix when you find it.

There are also consumables like collets that should be replaced every 6 months or so, depending on the level of use.
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Re: Z-Zero shifting mid-process

Post by mtylerfl »

Is it possible your Safe Z and/or Home Z position is set too high and causing your spindle to “top out” during your project run? Usually, this would halt the project, but maybe it’s just causing loss of Z position and keeps on going but with incorrect depths.
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Re: Z-Zero shifting mid-process

Post by Leo »

Yes I personally have had it happen to me.

The situation will be different depending on many different things.

More likely than not you are losing steps on the "Z" azis. The X & Y look fine.

What can cause it? Lot of things like - but NOT in order:

"Z" axis tops out. It retracts too high and hits the top of the axis.

Inertia - the "Z" axis reaches the top, in rapid, then descends - inertia in changing motion overcome the steppers and looses steps - this is what happened to me.

The tool was pushing too hard and the power needed was too much force and causes lost steps

Maybe your feedrate is too high in plunge

Maybe your machine is getting dirty and needs cleaning and lubricating. I needed to do that on my older machine daily.

To me, it looks like your issue is happening at the end - maybe the "Z" is doing a rapid up before starting the next row. I don't really know without watching your machine.
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MillAlien
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Re: Z-Zero shifting mid-process

Post by MillAlien »

Leo wrote:
Thu Jan 21, 2021 3:48 pm
Yes I personally have had it happen to me.

The situation will be different depending on many different things.

More likely than not you are losing steps on the "Z" azis. The X & Y look fine.

What can cause it? Lot of things like - but NOT in order:

"Z" axis tops out. It retracts too high and hits the top of the axis.

Inertia - the "Z" axis reaches the top, in rapid, then descends - inertia in changing motion overcome the steppers and looses steps - this is what happened to me.

The tool was pushing too hard and the power needed was too much force and causes lost steps

Maybe your feedrate is too high in plunge

Maybe your machine is getting dirty and needs cleaning and lubricating. I needed to do that on my older machine daily.

To me, it looks like your issue is happening at the end - maybe the "Z" is doing a rapid up before starting the next row. I don't really know without watching your machine.
These are terrific check points. I’ll start drilling through them.

One thing I’ve noted is that this problem has twice occurred well into the second hour of 4+ hour tool paths. Most of my jobs don’t run that long. That makes me think it’s a heat related problem, which in turn could be a lot of things that need tweaking. I’ve very new at this and don’t have much of a knowledge base.

As another respondent noted above, a maintenance overhaul is warranted - I have not done that although I have done superficial maintenance like keeping oil and coolant reservoirs filled and the machine clean.

And agreed on “know your machine” - I think I’ve delayed understanding it mechanically long enough and it’s obviously fine to roll up my sleeves.

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Re: Z-Zero shifting mid-process

Post by MillAlien »

Rcnewcomb wrote:
Thu Jan 21, 2021 4:13 am
o be honest, I'm a terrible mechanic and have been wary of every having to turn a screw on that thing from the day I bought it.
You have a good machine and you will actually be more comfortable with it when you get to know more about it -- I know I have with my machine.
100% agreed. It’s time to face my fear.

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Re: Z-Zero shifting mid-process

Post by Todd D »

Also don't forget the tip above a few posts that collets are consumable, recently I was having problems with bits slipping no matter haw hard they were tightened, new collet no more slipping,

I have never replaced a router collet in 30 years so never thought it was a thing, on cnc it is,

MillAlien
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Re: Z-Zero shifting mid-process

Post by MillAlien »

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.

The tech recommended cleaning the ball screw, lubricating the balls screw bearing set with white lithium grease and pausing jobs with 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 to that area sometimes can't maintain adequate lubrication on short travel hot zones during lengthy tool runs according to the tech - problem more common on their lighter duty IQ series but also the likely culprit on my Swift.

His diagnosis is consistent with my problem - I've not run long-duration tool paths before with a small Z-travel area and never paid any particular attention to the lubrication on the ball screw. I could be more aggressive with the pump on the reservoir as well.

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. Fingers crossed.

Kudos to Laguna customer service BTW - the tech called me within 5 minutes of my form query and discussed this problem at length, then sent me pics of what he was recommending using their training machine:
Spindle2.jpg

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Re: Z-Zero shifting mid-process

Post by MillAlien »

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.
Dropping Zero.JPG
I don’t think this is a lubrication issue – 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.

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Re: Z-Zero shifting mid-process

Post by Rcnewcomb »

What is the Z plunge rate you are using for the various toolpaths?
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MillAlien
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Re: Z-Zero shifting mid-process

Post by MillAlien »

Rcnewcomb wrote:
Thu Jan 28, 2021 3:47 am
What is the Z plunge rate you are using for the various toolpaths?
1/2 the feed rate.

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Re: Z-Zero shifting mid-process

Post by Rcnewcomb »

What is your plunge rate in inches per minute?
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