Not Z-Wobble - Bang Bang Bed Heating
August 10, 2017 08:00PM
I have seen a number of people fighting Z wobble with various exotic solutions and having limited success -- myself included. I recently installed a BLTouch and decided to determine conclusively if my issue was actually z-wobble. I introduced a substantial (about 10mm) Z / height difference across the heated bed on a diagonal. 3 Point levelling insures the plane of correction is flat so the result of this large diagonal tilt is that any X or Y movement also requires a Z correction. If the issue was z-wobble, I would no longer see linear bands, instead that wobble would have a woven look on any X or Y surface.

I was surprised to see that linear horizontal bands remained which led me back to Google and a couple of threads on these forums indicating it might be Bang Bang bed heating flexing the bed through fully on then fully off heating cycles. Since those threads didn't include images here are the results:



Problem solved! For anyone looking to make the change, these lines need to be adjusted in Marlin firmware's Configuration.h:

#define PIDTEMPBED
// ... Next section down ...
//#define BED_LIMIT_SWITCHING

Incidentally, for an Anet A8 (220 x 220 PCB bed), the following bed PID settings work well for me (YMMV):
M304 P97.1 I1.41 D800   ; Set the bed PID values
M500   ; Store to EEPROM

Many thanks to the people pointing in the right direction in these threads:
PID forum post 1
PID forum post 2

Edited 2 time(s). Last edit at 08/12/2017 12:37PM by denos.
Re: Not Z-Wobble - Bang Bang Bed Heating
August 12, 2017 01:52AM
To bad, we can't see a video of such a tilted bed! 100mm height difference, how is that possible?
Re: Not Z-Wobble - Bang Bang Bed Heating
August 12, 2017 08:25AM
What if do not use either, does this mean I should choose "#define PIDTEMPBED"


//#define PIDTEMPBED
//#define BED_LIMIT_SWITCHING

Edited 1 time(s). Last edit at 08/12/2017 01:25PM by Roberts_Clif.
Re: Not Z-Wobble - Bang Bang Bed Heating
August 12, 2017 12:32PM
Quote
o_lampe
To bad, we can't see a video of such a tilted bed! 100mm height difference, how is that possible?

Doh! That was a typo, 1cm / 10mm, not 10cm. Thanks for pointing it out.

Edited 1 time(s). Last edit at 08/12/2017 12:38PM by denos.
Re: Not Z-Wobble - Bang Bang Bed Heating
August 12, 2017 12:34PM
Quote
Roberts_Clif
What is if do not use either, does this mean I should choose "#define PIDTEMPBED"


//#define PIDTEMPBED
//#define BED_LIMIT_SWITCHING

I'm guessing that if neither are defined that it goes with bang-bang as that will work in every scenario without tuning. So maybe it's just a matter of defining PIDTEMPBED.
Re: Not Z-Wobble - Bang Bang Bed Heating
August 12, 2017 01:25PM
Quote
denos
Quote
Roberts_Clif
What if do not use either, does this mean I should choose "#define PIDTEMPBED"


//#define PIDTEMPBED
//#define BED_LIMIT_SWITCHING

I'm guessing that if neither are defined that it goes with bang-bang as that will work in every scenario without tuning. So maybe it's just a matter of defining PIDTEMPBED.

Thank you
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