very strange Lines on Prints - Firmware issue?

[Tim N.]

@Phaedrux Yes. I tried PID as well as Bang-Bang but no luck. However I switched back to Bang bang since the PWM signal from the PID control caused more audible noise.

Edit: I am not sure I covered this explicitly in my tests. I will rerun this right now, to be 100% sure.

[Phaedrux]

Do a test print with the bed heater off entirely to verify.

[Tim N.]

@Phaedrux good idea!

[Tim N.]

@Phaedrux

I did Some tests now, and on the first one was still some decent Z banding - but in a random order!
Then I placed a model right in the middle of the bed (if it would be because of thermal expansion, then it should be most visible there, I think) and run a test without and with Bed heating (Bang-Bang).

This is the Result:

Hell YEAH! This was it!
@Phaedrux can I offer you a Coffee?

Fun fact: I measured the cycle time for the Bed heater turning on: It takes between 15-17 Seconds

So the next question is: Does PID solve the problem entirely?
And how common is this problem? I searched a lot for types of z wobble, but this one is new to me, although it makes a lot of sense.

Edit: Is there a way to change the name of the topic (or mark it as solved)?

[theruttmeister]

Cool!

Have you tried printing in a corner of the bed?

[Tim N.]

@theruttmeister yes. I did most of my testprints in the corner. However with Bang-Bang ON it is still noticeable. I am trying it now it PID PWM mode.

[Dad003]

it look like Z banding like some said. threaded rod must be flexing under the weight

[Tim N.]

@Dad003 I think the remaining artifacts could be to some amount z-wobble. However, the biggest point was definitely the Bang-Bang Mode.

Now here is something interesting: I changed to PID-Mode and the wobble is very present like in Bang-Bang mode! I'm running a new auto tune run now. I hope, that helps.

[Phaedrux]

PID tuning should help quite a bit by keeping the temp steady, but from what I know about the Tronxy bed is that it's very large and very thin and when current is applied it causes it to deform. I would think that once the bed is at temp and stable it shouldn't be much of a problem.

You can also experiment with different PWM frequencies in the M950 command for the bed heater.

https://duet3d.dozuki.com/Wiki/Gcode?revisionid=HEAD#Section_M950_Create_heater_fan_or_GPIO_servo_pin

Q500 is the default. Can try higher or lower.

Also make sure you're tuning the bed from cold.

[Tim N.]

I used M307 with the Fnnn parameter to set the frequency without luck. But Qnn on M950 works! Thanks @Phaedrux !
Running now inaudible at 20 Hz.
Does anybody know if this could be unhealthy for the PSU Capacitors?

[percar]

A number of years ago when i was printing on a thick aluminum plate 12mm cast fixture plate i was having the same issue using bang bang for the bed heater. If you put a dial indictor on the place you will actually see the dial indicator moving up to .2mm during heating. I changed the bed heater to PID and the issue was greatly reduced. One issue with aluminum is the thermal expansion which is why i have gone to borosilicate glass and all the expansion problems went away.