Help with Plunge Rate/Z Axis Speeds for 3D Milling

I tried reducing my Velocity and Acceleration values from 3000 and 400, respectively, to 2000 and 200, but I still lost steps. I then reduced it again to 1000 and 100, respectively.

In Aspire, I’m using 1000 mm/min (~16 mm/sec) for my feed rate and 120 mm/min (2 mm/sec) for my plunge rate on my 3D finishing tool path. I wondered if it could be Aspire generating a bad tool path, but I verified my tool was at the surface of my spoil board before starting the tool path by hitting ‘Goto Zero’ in UCCNC and it drops into the spoil board, cutting it, when I hit ‘Goto Zero’ after I run part of the tool path, so the system is definitely losing steps.

I can jog the axis up and down at full speed as fast as I can using the hotkeys on my keyboard and I can’t replicate the step loss. It only occurs when I’m running the 3D tool path. I have full range of movement on the axis without binding.

Are there any other suggestions you can offer?

Well, just to keep this thread updated with things I've tried, I wiped down and relubricated all of my axis, paying special attention to the Z axis. Didn't make any difference. Can still job 100% to my heart's content, but steps are getting lost when I run the 3D tool path. I've long since given up on trying this path on real material and am just air cutting. Zero to my spoil board surface, run tool path, 'Goto Zero' afterward and I'm cutting into the spoil board. I even tried a 20 mm/min plunge rate to see if a super slow feed would help.

Not sure what else to do at this point. Though I've seen no evidence of it, it's possible I'm getting electrical interference somewhere, but it's only affecting the Z axis if I am. What I really think it is, is that the stepper can't handle the very small, quick movements required to cut the lithophane and is stalling out.

If I have any volunteers, I can send you either the Aspire project file or the G code itself to try it out and see if it works on your machine. Running the tool path for 10 minutes (it would run for 2.5 hrs for the whole thing) is usually sufficient to see if you've lost steps. You can just air cut rather than cut into any material.

~Dan

HI
If I understand correctly you are setting your z=0 at the bottom of the material with Aspire and Z=0 at the surface of your material?

The machine is plunging to the bottom of the material and starts cutting. You have to set the Z=0 to the top of the material and then zeroing your machine also at the top of the material or I understand something wrong you are doing...

Regards
Tom

Tom,

Thank you for the reply. However, no, I'm afraid you have misunderstood or I have described the issue poorly. I'm am setting Z=0 in Aspire to the Machine Bed (bottom of the material) and I am zeroing my cutting to the machine bed before starting the tool path, not the material surface. The machine is not plunging all the way through the material when it starts cutting. It's losing steps and cutting all the way through the material when it shouldn't. It should leave ~0.03 - 0.04" at the lowest part of the lithophane.

What little I've looked at it as it's a 7 MB file, the tool path that is generated seems fine. It's just using a bunch of G1 commands and never goes below Z = 1. I've been in contact with a support engineer and they ran my tool path on their machine and said they have no issues.

My issue is that, after I run part of the tool path, say 10 minutes or so, I'll 'Stop Cycle' and send the cutter to zero with 'Goto Zero' and I'm now cutting into my spoil board (machine bed as far as the job is concerned), so I've lost steps somehow.

The support engineer thought my rollers might be too tight, so I took the Z axis apart last night, cleaned everything up, tested the extrusion against the rollers till I had only just taken up the wiggle, put everything back together, and lubricated well. At the engineer's suggestion, I even added a drop of oil to the lead screw to try and make it smoother. Still having the issue.

I then tried tightening the rollers by 1/4 turn and rerunning the test twice, tightening another 1/4 turn in between, but it still failed, cutting into the spoil board after the tool path ran. I can still jog up and down at 100% speed without binding.

~Dan

Danny,

It looks like your machine is fine tuned baut still loosing steps.
Have you checked you computer?
Make sure that the USB/Parrallel connection stays alive and that the computer does as little background duties or none.
Because it is a large toolpath-file I think your problem lies in the continuancy between the computer connection with the steppie.

HI

If you zero and jog the Z axis up and down several times do you loose steps ? or only when the machine cuts?
Just to rule out some tricky things, is the coupler between leadscrew and motor fastened, not that it looses steps there?

Try setting z=0 to the top of the material and zero Z on the material surface.
Important to find out is it a mechanical or electronical problem...

Thanks for the replies.

CNCMiller, I've done my best to make sure background processes don't interfere and I can't say I've seen the machine stutter at all while running the tool path, but if it's subtly dropping a command here or there, I'm not sure I'd be able to tell. As best as I can tell, the X and Y coordinates are still correct. It's just the Z that is wrong. I've disabled the screen saver, putting disks to sleep, and turning the display off in the power manager. I admit I am running UCCNC in a Windows VM in VMWare Fusion on my Mac, which isn't the same as bare metal. If that is causing an issue at all, I couldn't say. I believe Stepcraft has a blurb on their site about users using a Windows VM on Macs without issue, but that doesn't mean it isn't part of the problem, I guess.

hb9dod, yes, I tried jogging the axis up and down as rapidly as I could with two fingers on the page up and page down key. Never managed to get it to bind or lose steps that way. When I took the axis apart, I triple checked the couplers and never found anything loose. When I initially assembled the machine, I used weak strength Loctite on the grub screws so they wouldn't back out.

I can try setting my Z reference point to the top of my material, but that was what I was doing when I first tried cutting these lithophanes and it failed the same way. I switched to the bottom on the advise of people who have cut many lithophanes as that is the best way to ensure the critical 0.03 - 0.04" minimum height for the lightest parts. The material thickness becomes irrelevant if you reference from the bottom.

If it weren't for the fact I'm not losing any X or Y steps as well, I'd suspect CNCMiller's suggestion might be my issue, but it only seems to be Z that is being lost.

~Dan

I'm going to try this again tonight with my plotter pen attachment to see if I experience the same issues. That will also help me verify the X and Y aren't being lost. I spoke with certainty above that they weren't, but, since I'm cutting a hole in the spoil board at the end, it's hard to say with 100% certainty that I'm exactly at the same X and Y position. They don't appear to be off, but if the are off just a little bit, that would certainly be telling.

~Dan

Tested a few more things tonight. I borrowed a Windows laptop so I'm running directly on hardware rather than through a VM on my Mac. Made no difference.

I also made sure it was only my Z axis losing steps. By putting a piece of tape down and cutting into it slightly. After the run, it cut directly in the same spot, but deeper.

I also ran with the spindle off to see if it might be causing some interference. Made no difference.

I also used a multimeter to verify my ground wire and the bottom plate are at the same potential. They were. I can only assume, that being the case, that the system is grounded properly.

Not sure what else I can try.

~Dan

Hi,

Some thoughts!!

Assuming that the problem only exists on the Z-axis (you've already checked this I take it)

1) If only the Z axis is affected, is it possible to remove all the X and Y movements from the Gcode and run only the Z commands to see if that isolates the problem?

2) Drive the X-axis stepper with Z-axis code (swap the motor coils) and see if the problem repeats on the X-axis or remains on the Z-axis

3) Remove the parallel card and clean all the connector contacts with IPA .

4) Generate a test Gcode file with only Z movements - this ought to run for several minutes to give a chance of catching the problem.

IMHO two 1/4 turns on the roller preload is asking for trouble - its likely to damage the roller track due to extreme pressure at the contact points - your technique of just removing the "wiggle" is one I have adopted, and have had no known problems with accuracy .

Peter

Danny,

If its like Peter says, it only happens in your Z-axis and halfway through your project, you have fantom in your machine 👿 or something else is happening.

Lets think about this.
- the Z-axis travel goes smooth, no binding on the travel?
- the G-code is correct (checked on other machine)?
- connection between computer and steppie is sound?

Then I don't think it is in your hardware.

But there is definitely a problem!
Why is the zero position of the z-axis changed during operation?
- there is no resetting of the zero position somewhere in the G-code?
- UCCNC does not reset the zero position due to........what for reason ?
- are all wires of the stepper motor are undamaged? (no wire failure?)
- is there a loose contact on the mainboard or a printfailure (broken spur?)

It is very difficult to isolate the problem and it keeps you away from milling but keep up the good work one day it will work

Hmm... the plot thickens!

Thank you all for the suggestions. I'm fortunate to live relatively close to work, so I zipped home for lunch and tried running an X-only tool path and also a Z-only tool path. Essentially, I edited my full tool path file to change the G1 commands to only have one axis.

I let the X-only tool path run for 10 minutes, usually enough to replicate my issues, and then sent the machine back to zero. I kind of expected it, but I had lost no steps.

I then ran my Z-only tool path for 5-10 minutes, stopped it, and sent the machine to zero. I'd lost no steps!

So, now the question is why am I losing steps when the G1 commands have X, Y, and Z in them? It is a UCCNC transmission issue? Or am I getting some sort of electrical interference between my X, Y, and Z steppers? If the latter, what can I do about it? The way they have you run the leads, I don't see how I can get the leads away from each other.

Suggestions appreciated!

Thanks,
Dan

Well, just wanted to report that I shortened all my wires to eliminate bundles and, as soon as I run the tool path with all the axes running, it fails in the same way. So, it wasn't due to the long servo wires.

I checked that my ground is at least getting to the control board for the E-stop and end switches, but I wasn't able to find a servo wire that had ground connectivity. Should I have?

~Dan

I additionally tried running tool paths with X and Z axis only and Y and Z axis only. Stopped the cycle after 15 minutes. They both lost steps on the Z axis.

I think I'm throwing in the towel at this point. Going to sell this system off and cut my losses. Can't imagine trying to ship this, so going to have to sell local. If there is someone in the Northern Virginia area that wants a machine for 50% off, it's yours. Latest HF-500 spindle for $400. Going to save up and try and get an Axiom Pro machine.

~Dan