Trying to troubleshoot some jerky motion in cuts

[Ken Rychlik]

I fix and sell them. I’m on number 6 this year. I do most brands but remember the axyz voltage issue. I would run the full lengtb and measure both sides. I would change pinion gears if they are not running together. I don’t think there is a way to electronically correct. If someone charged one pinion gear and not the other that could cause what you have.

[muibubbles]

AH cool, just AXYZ machines? How do you find the wear and tear on them? Do they generally last long or require replacements? Do you know if generally the rack or pinion wears first or equally? I was able to dial in my speeds and feeds and get beautiful cuts (for a cnc router) in the y direction. (first 3 pics, top is with the new feeds and speeds, bottom is a little worse than what i was getting prior)

However when i cut diagonals I am still plagued with this stair stepping effect and similar with the arcs but this looks slightly better than before. This is driving me crazy! (last 3 pics)

[Ken Rychlik]

Set up to air cut the file. Next change to single step on your screen. This will run one line at a time. When you do the straight line it should run that whole section in one move. See how many segments are on the choppy curve

[cnckeith]

post the g code program

[cnckeith]

you have y axis at 1600 steps per rev at 1.754 turns per rev. this is pretty low resolution for cutting aluminum. if you are using this machine like a bridge mill you need to gear down more which would increase overall turns ratio and increase the steps per rev to 3200. Milling machines and bridge mills that cut parts like this operate in the 2.5 to 5 turns per inch range while are typically in the 4000-32768 steps per rev range.

[muibubbles]

Set up to air cut the file. Next change to single step on your screen. This will run one line at a time. When you do the straight line it should run that whole section in one move. See how many segments are on the choppy curve

I just tried it and all the codes seem to be good. diagonals and arc are one line of code (minus transition to each feature)

post the g code program

Attached

you have y axis at 1600 steps per rev at 1.754 turns per rev. this is pretty low resolution for cutting aluminum. if you are using this machine like a bridge mill you need to gear down more which would increase overall turns ratio and increase the steps per rev to 3200. Milling machines and bridge mills that cut parts like this operate in the 2.5 to 5 turns per inch range while are typically in the 4000-32768 steps per rev range.

The previous report I was testing if I could see any noticeable difference between 1600 and 3200 stepping.
My current are configured to the recommendations you posted here: https://centroidcncforum.com/viewtopic.php?f=63&t=1801 and I've attached the current report. All my settings fall within the recommended diagram for the router settings. But should I be adjusting them to the milling/lathe settings?

I'm a bit lost why I should gear down more vs just increase the micro stepping to 3200 if I'm trying to increase my resolution? Where would I see benefits changing my gearing? This is the gearing it came from the manufacture and my other cnc router(avid cnc) is geared similarly, 3:1. Does my gearing need to be different strictly because I am trying to cut thicker aluminum? (my motors are rated for 880oz-in holding torque if that makes any difference)

Also this just came to mind. The cuts from the initial post have shallower random lines and that was with 3200 steps per rev. The last cut has deeper vertical lines however they seem to be very uniform and this is with microstepping set at 1600. Coincidence or does this reveal an issue?

Thank you guys for all your feedback!

[Ken Rychlik]

I have noticed a little smoother results with 3200. At some point I think you may be seeing the tooth patern of the gears in your cuts. It might also be material vibrating on the table when cutting. Without going to a mill you are not going to get results like a mill.

[muibubbles]

I have noticed a little smoother results with 3200. At some point I think you may be seeing the tooth patern of the gears in your cuts. It might also be material vibrating on the table when cutting. Without going to a mill you are not going to get results like a mill.

Agreed, I'm going to switch it back to 3200 today. The last cut definitely seems like I'm seeing the tooth pattern as the "chatter lines" are so consistently space with matching "chatter depths" however, I just can't wrap my head around why this only happens on diagonal cuts when I can get my horizontal and vertical cuts near perfect. This part was locked down by 6" machining vice so I don't think work holding is the issue in this case.

Another thing I did notice is although my finishing pass tool path is set to 15IPM, I say it peak at 20IPM on CNC12 which was weird. I do have smooth stepping ON in CNC12. I know it should decrease speeds in corners but would it increase feed rate on straights?

[Gary Campbell]

The cuts from the initial post have shallower random lines and that was with 3200 steps per rev. The last cut has deeper vertical lines however they seem to be very uniform and this is with microstepping set at 1600. Coincidence or does this reveal an issue?

Yes. Not enough mechanical reduction resulting in a disparity between the commanded and actual position. See this white paper:
https://peoplevine.blob.core.windows.ne ... _0214A.pdf

Also, you may also be suffering from an inability, or a lag in achieving actual position due to the length and low strength of your belts, which seem undersized to me. They appear to be "XL-3/8", where if I was making an aluminum cutting machine (and I have built a number of them) I use 25mm HTD with much shorter distance between the pulleys.

For example, the one that cut the best used a 5:1 planetary gearbox INTO a 4.5:1 HTD (25mm) belt reduction into a helical spur gear of about 26mm (~1.023") which resulted into a "turns ratio" of ~6.09 where yours is ~1.18, mine being over 5 times the mechanical reduction. Add to that I was using a ClearPath servo with 6400 native counts per rev resulting in ~27,093 counts per inch of travel where your setup yields ~5927 theoretical steps per inch.

I say theoretical because as the above linked white paper shows that as you increase microstepping levels the ability to hold that position decreases and the hysteresis of commanded vs. actual increases.

[muibubbles]

Gary,

That makes so much sense, I think it finally clicked and now I am understanding how resolution would affect my diagonal and arc cuts!
Thank you for the link, I will give it a read now.

The belts and pulleys may very well be undersized, everything mechanical on the machine is how it came from the factory, the only components I swapped out were the stepper drivers and acorn board. AXYZ generally makes CNC machines for the sign making industry and the prior owner was using the table to cut solid surface materials like Corian etc (hence the enormous table size).

You are correct on the belt size. Would it make sense to mechanically reduce my gearing if predominately cut aluminum sheet metal under .1" or will it only be beneficial if I plan to do more aluminum "milling" operations?

Do you have a build thread of the aluminum cutting CNC you built? (Is it the ultimate woodworking machine on your youtube channel?)