Sometimes jittery cuts

[ShawnM]

Your steps/rev are WAY outside the sweet spot for plasma. It states in the chart that you'll get jerky motion with your current settings. You said you have a belt reduction, what ratio is it? Your steps/rev are .43 for both X and Y and they should be at a minimum of 1.5 to 3. You'll be hard pressed to get any good cuts with this setup. Your Z axis is set to 1.

Please also post pics/screen shots of the DMM settings you have in the DYN software.

[_Duke_]

the belt reduction is 1:3.25
that gives a turns per inch of about 1.4, which is still on the low end of good. But these are 1.3kw servo motors, so plenty of grunt.
I stepped up the steps/rev to 6400 from 4000 and ran the auto tuning feature in the DMM software. The before and after screen grabs of the tuning window are at the bottom of the build thread album. Let me know if you think I should go higher with the steps/rev, like 8000?
sorry for any rookie mistakes, I'm new to ac servos, this is my first time configuring them

[ShawnM]

the belt reduction is 1:3.25
that gives a turns per inch of about 1.4, which is still on the low end of good. But these are 1.3kw servo motors, so plenty of grunt.
I stepped up the steps/rev to 6400 from 4000 and ran the auto tuning feature in the DMM software. The before and after screen grabs of the tuning window are at the bottom of the build thread album. Let me know if you think I should go higher with the steps/rev, like 8000?
sorry for any rookie mistakes, I'm new to ac servos, this is my first time configuring them

If you look at your last report from 1/3/2024 you have your step/rev set at .43668 and .43455, there's no 1 in front of either of those numbers. Doesn't matter if they are 5kw motors with and endless supply of power, it'll never cut good with your current steps/rev. You might want to do the math again and see if you have these set correctly.

[jcoldon]

first off using a dmm ac servo with 3 to 1 s reduction my guess 1.5 inch pinion you have. based on moving 1.4 inch per rev. not going to work .. you need 10 to 1 reduction with 2 inch or 1.5 inch pinion gear . 3 to 1 setup for stepper most 3 to 1 run 1 inch pinion gear to get 1 rev to 1 inch movement. . Dmm has a motor gear program that allow you to size the motor drive system i posted it on my fb page cnc plasma table builders . that gantry large heavy not designed to run at 400 ipm with high acceleration that hypertherm requires . i ask this how smooth is the z axis my guess it has a 5 mm pitch ball screw that about 5 to 1 reduction . you cant push a heave gantry running motor at low rpm no matter how big the motor . the torc curve drops off on dmm ac servo at low speeds . this table was designed to cut thick heavy plate were slow speeds were required . if I'm correct that table only has 1 Y axis motor were it should have 2 motors 1 on each side . were 1 motor y table will not be smooth on high speeds . 10 to 1 reduction get rid belt reduction that one you have lack resolution most likely lot back lash

[_Duke_]

Well guys, I feel like a bit of an idiot.
I was wrong when I said the belt reduction is 1:3.25 - it's actually a double belt reduction. The 2nd belt that goes to the pinion is under a cover that I can't get to easily. But looking at it through a small gap, it looks about the same as the first belt setup, so that would put the reduction around 1:6.5
After increasing the resolution and running the auto tuning, the jitters seem to have gone away.
I did my first real test cut after the changes today, some 16ga steel at 350ipm. Best cuts I've gotten out of the machine to date.
Still don't know why it was having such a bad hair day the other day doing all that weird stuff with the restart buttons, cutting square circles, etc.
I'll keep playing with it and let you know if I come up with any smoking guns.

Jeff- I did a search on your fbook group and couldn't turn up the Dynamic Motor Motion motor gear program you mentioned. Perhaps you could post it again here?

Thanks everybody for all your help

[Joey]

Good to hear Duke
learned something new from this. Low speed with low resolution was pretty wild

What is your steps per/rev and overall turns ratio now?

Did you update to 5.08 yet?