Z axis not consistent (missing steps?)

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Nglcncnewb
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Z axis not consistent (missing steps?)

Post by Nglcncnewb »

Hello all,

Let me start by thanking you all in advance for any help and also apologizing in advance for my significant lack of experience, knowledge and information. ;)

So, I have an Acorn cnc table router ~4'x8'. I've dialed in the x and y axis pretty well so have little to no concern those are working fine.

The z axis on the other hand I have not been able to get working consistently/accurately.

To try and explain:

I have a simple program to cut a hole about 1 inch in diameter and about 1/4 inch deep via two depth cuts. The first time the program runs, it seems to run just fine. But if I change nothing, and run the program again, it will cut a deeper and deeper hole. Again the x and y axis fall in the exact same spots, but the z axis looses steps downwards.

For example (and some data to help maybe?). First cut the hole is .155 deep (which I know is not actually 1/4 inch, but I'm not concerned about that yet). Second cut (again, changing nothing, simply hitting run again after the program completes), and the hole is now .219 deep. Run it again, and the hole is now .250 deep. A 4th run and the depth of the hole is now .320 deep. Keep in mind the machine thinks it is going back to the false home I set it to go to after each run (+17.5522), but it is not actually going back to the same home position (again moving down incrementally; .126 away from the limit switch, then .175 away, then .200 away and finally .260 away).

One other bit that may be of some information. When I do the calculations to dial in the RPI, I can do the math for the x and y axis and the numbers dial in closer and closer to a pretty decent tolerance. But when I do that for the z axis, it seems to get closer and closer, then it goes way off. I'll work it some more and it will get closer an closer, then way off again. Sometimes it's way off + and other times it will be way off in the - direction. I can never really get it dialed in because of that, but I believe it's currently as close as I can get it.

I hope that's enough information to give you all some ideas on what to try next. I've been working on this on my own now for quite some time, but have no experience with acorn prior to this and very little assistance has made this quite challenging. Please let me know if you all have any clue.

Thank you again in advance!

DTucker
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cnckeith
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Re: Z axis not consistent (missing steps?)

Post by cnckeith »

photos of Z axis please.. make google photo album and post link to that album here.
photos of electrical cabinet showing wiring and make model of axis motor drives etc.
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
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cnckeith
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Re: Z axis not consistent (missing steps?)

Post by cnckeith »

and upgrade to v4.80.. report shows v4.50 on the system. which is 3 years old. update to latest v4.80 so we are all using the same software and can help you. update instructions and free download of v4.80 is here.
https://www.centroidcnc.com/centroid_di ... loads.html
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
tblough
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Re: Z axis not consistent (missing steps?)

Post by tblough »

Nglcncnewb wrote: Tue Oct 04, 2022 2:33 pm For example (and some data to help maybe?). First cut the hole is .155 deep (which I know is not actually 1/4 inch, but I'm not concerned about that yet). Second cut (again, changing nothing, simply hitting run again after the program completes), and the hole is now .219 deep. Run it again, and the hole is now .250 deep. A 4th run and the depth of the hole is now .320 deep. Keep in mind the machine thinks it is going back to the false home I set it to go to after each run (+17.5522), but it is not actually going back to the same home position (again moving down incrementally; .126 away from the limit switch, then .175 away, then .200 away and finally .260 away).
The scenario above is EXACTLY what would happen if you are loosing steps. Are you using stepper motors or hybrid servos with encoders? IF the latter, do you have the driver error signal hooked up to the Acorn?

Try reducing the feedrates (and that includes the rapid G0 moves) by turning the feedrate override down and see if the issue still occurs. If that fixes the issue, then your accelerations are set too fast for your drive/stepper combination, or your drive/stepper is sized too small for your system.

If the problem still occurs at lower feedrates, try it again with the spindle off. If that fixes the problem, then you have an EMI problem. Check the shielding of your motor cables and step and direction signal cables and make sure they are properly grounded.
Cheers,

Tom
Confidence is the feeling you have before you fully understand the situation.
I have CDO. It's like OCD, but the letters are where they should be.
Nglcncnewb
Posts: 3
Joined: Tue Oct 04, 2022 11:56 am
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Re: Z axis not consistent (missing steps?)

Post by Nglcncnewb »

Thank you all for your responses.. I hope I can deliver on your requests.

To cnckeith:

The link to drive w/ pics:

https://drive.google.com/drive/folders/ ... sp=sharing

Also, I don't feel comfortable enough to upgrade to v. 4.8 yet, I'm sorry. I know that may make things more difficult, but I just don't know enough to feel comfortable making major changes. Especially since supposedly this router worked fine ~3 years ago when we got it but before it was moved into our shop. If I must update I will, but I'd like to leave that as a latter resort if possible.

To tblough:

The problem is it's not consistent. It acts like it's losing steps almost randomly. Like it's missing a step only a part of the time. But, to answer your questions; I don't know :lol: I hope the pics I took will help answer those questions. I believe I'm using stepper motors, but I can't answer the error signal question.

Also, I believe the feed rate is relatively low, since that was a concern at one point so someone we worked with turned it way down. One problem I have is I don't know how to configure that anyway :oops:

I almost always do my tests with the spindle off (unless I'm attempting a cut, such as the above). And we have already done a variety of things to minimize/eliminate EMI problems including shielding and ferrule filters etc. to no avail.

I'll try a few different speed rates via MDI an see if I see any change in behavior.

Thanks again!

DTucker
cnckeith
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Re: Z axis not consistent (missing steps?)

Post by cnckeith »

thanks for the photos.
i would start looking for mechanical issues. loose z axis motor belt drive pulleys? no keyway? loose keyway?
something is loose and slipping etc.
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
Nglcncnewb
Posts: 3
Joined: Tue Oct 04, 2022 11:56 am
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CNC Control System Serial Number: 7804734C5EE9-0325191808
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CNC12: Yes
CNC11: No
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Re: Z axis not consistent (missing steps?)

Post by Nglcncnewb »

Pulleys and belts all seem reasonably tight (no more than about a 1/2 in play or so). I'm not sure what the keyway would be let alone if it's loose (keyway in the gear/motor sprocket? Also seems tight).

Everything feels tight. Backlash seems minimal, belts and pulleys seem okay, no real play in anything out of the ordinary. I've tightened my limit switches down to account for play in the send home, created false homes to account for potential loss via limit switches, and re-calibrated RPI ad nauseam.

At this point someone has recommended swapping the encoder out, but that's a ~$1000 fix (which would be great if I knew that would fix it, but supposedly the motor and encoder have already been swapped out before, sooo... plus I'm not sure I'm comfortable doing that alone yet either).

Anyway, I know this is a tough one. I have had a few 'experts' take a look to no avail. Just hoping that a broader scope of users may lend insight.

Thanks again!!
Nigelo
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E415F6F70BC3-0318203049
98F07B91FC6B-0123236802
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Re: Z axis not consistent (missing steps?)

Post by Nigelo »

Daniel

You say that backlash is minimal but your report shows you have just changed the Z lash compensation from 0.003" to 0.010" which itself raises several points:
  • 10 thou, really? Is this a mistake or if not, you need to track down the mechanical cause as its way more what any software can correct and is certainly NOT minimal as you suggest. Even 3 thou is above what the comp can reliably correct
  • A straight change from 3 to 10 thou suggests that you may have rechecked the backlash without zeroing the comp setting / rehoming first. This is not the practice I follow as it leads to errors
  • If 10 thou is correct you need to find and correct the mechanical problem before even touching the comp settings
You have also stated in an earlier post
Pulleys and belts all seem reasonably tight (no more than about a 1/2 in play or so)
What does 0.5 inch refer to as this seems massive?

Finally, you have changed comp settings and yet you state you don't feel comfortable in upgrading your very old s/w version 4.5!! As support for v4.5 has long since finished this should be done ASAP if not before doing anything else. Otherwise, it makes it more difficult for everyone to give you the most accurate advice.

If you are competent to change settings, you ARE more than competent to upgrade the s/w. Just be sure to follow the "Update Instructions" about half way down in Keith's 1st post here https://centroidcncforum.com/viewtopic.php?f=60&t=7354

Hope this helps
"You can lead a horse to water but you cannot force it to drink"
Hope this helps
Nigel
tblough
Posts: 3072
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100327
102696
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7804732B977B-0624192192
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Re: Z axis not consistent (missing steps?)

Post by tblough »

If you don't upgrade your CNC12, then we can't load your report on our systems to help with debugging.
Cheers,

Tom
Confidence is the feeling you have before you fully understand the situation.
I have CDO. It's like OCD, but the letters are where they should be.
ShawnM
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Re: Z axis not consistent (missing steps?)

Post by ShawnM »

Nigelo wrote: Thu Oct 06, 2022 7:15 am You have also stated in an earlier post
Pulleys and belts all seem reasonably tight (no more than about a 1/2 in play or so)
What does 0.5 inch refer to as this seems massive?
I saw this also and wondered about what he meant. If you have 1/2" deflection in your belts this is a problem. They are WAY too loose.

And be sure to follow the update instructions to the letter since you are upgrading from such an old version. There's a document just for updating from older versions on the linked page below. Here's the link to the download page AND the install instructions.

https://www.centroidcnc.com/centroid_di ... loads.html
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