# Avid cnc Z axis



## Huw (9 mo ago)

Hi all, I’m a new member based in the uk, I have a avid cnc pro, and have always had problems with the Z Axis, what happens is I zero the Z on the job then when I start the program the Z travels up to its home the spindle starts and then it travels down to make the cut sometimes at this point I notice it isn’t down enough (when engraving). When I bring the Z to zero it is now about 1.8mm off the job (1.8mm seems consistent) I will then re-zero off the job again and I seems to work. Any ideas would be greatly received.


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## difalkner (Jan 3, 2012)

Backlash would be my first suggestion.


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## gwilki (Nov 12, 2012)

If it's always off by 1.8mm and only after the Z rises to set off the limit switch, I would suggest that your homing settings are off by 1.8mm. When you re-zero Z, it works. But this time, Z does not rise to set off the limit switch. Correct? 

If so, I believe the limit switch/homing routine is the problem.


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## Huw (9 mo ago)

gwilki said:


> If it's always off by 1.8mm and only after the Z rises to set off the limit switch, I would suggest that your homing settings are off by 1.8mm. When you re-zero Z, it works. But this time, Z does not rise to set off the limit switch. Correct?
> 
> If so, I believe the limit switch/homing routine is the problem.


hi firstly thanks for replying to my post, every time the cycle starts from ‘work zero’ it goes up to the limit sensor before the spindle starts I’m sure it’s a offset issue possibly Mach4 or something that’s not setup correctly rather than backlash as someone else mentioned. Having said that my startup procedure is, home all axis, go to the corner of material and zero X and Y, bring the Z (cutter) down to the material so it touches and zero, I then lift it and ‘work home’ the machine (usually because I’ve moved the X or Y as to not damage my work) and start cycle, the Z goes up spindle start and goes down to start the cut, I realise it’s cutting shallow or not at all, stop the machine discover the 1.8mm discrepancy re-zero the Z ‘work home’ and start the cycle, second time great!


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## difalkner (Jan 3, 2012)

I use Mach4 and when I start a job it doesn't home Z. I wonder if it's something in your Post Processor telling it to do that each time...


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## Huw (9 mo ago)

difalkner said:


> I use Mach4 and when I start a job it doesn't home Z. I wonder if it's something in your Post Processor telling it to do that each time...


Yeah I think there is something something that maybe set with that offset just not sure where, I have a touch plate and stopped using it because of this reason, at the moment I can get round it, think it would become a major issue on multi tool more complex parts!


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## jw2170 (Jan 24, 2008)

Welcome to the forum, @Huw


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## old55 (Aug 11, 2013)

Welcome to the forum @Huw


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## Huw (9 mo ago)

The team at ‘Avid CNC’ have sent me a link to a Mach4 update which may resolve the issue fingers crossed, if not I might do a video on the issue and post it on my new YouTube channel https://youtube.com/user/you7227 which is a bit crude but improving 😋.
Thanks for your help and welcomes will let you know the outcome


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## lucian_m_canada (9 mo ago)

I had something similar, but in my case it was triggering an over travel (out of soft limits) error.
It ended up being the tool length. I was using the M6 routine, trying to automatically change the tool length. (I have an ATC spindle)
Check the tool length in the tool table and make sure it is ZERO


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## jw2170 (Jan 24, 2008)

G'day Lucian, welcome to the forum.


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## old55 (Aug 11, 2013)

Welcome to the forum @lucian_m_canada


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## Huw (9 mo ago)

lucian_m_canada said:


> I had something similar, but in my case it was triggering an over travel (out of soft limits) error.
> It ended up being the tool length. I was using the M6 routine, trying to automatically change the tool length. (I have an ATC spindle)
> Check the tool length in the tool table and make sure it is ZERO


Thanks for this advice!!
So here’s what it seems to have been the issue like you said was in the tool table, the first ‘tool length’ was down as 2mm the second ‘tool length’ was 1.5mm and the rest is at 0mm so I set them all to zero and it seems fine. It’s something I haven’t setup or looked at in detail (must have messed around when I first got the machine).
appreciate your input and sharing your experience!

regards
Huw


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