Welcome! Log In Create A New Profile

Advanced

Äuto bed leveling only once in a while

Posted by victorjung 
Äuto bed leveling only once in a while
November 22, 2015 02:14PM
Hello all, I am using auto bed levelling on marlin for while now and i am really happy with it, except that it's take close to a minute (9 points).
So I thought it would be great if you can run it frome time to time, note some values, and on every print correct Z axis according to those values without re-sensing any time.
I am using marlin and didn't found anything to do that.... Anybody knows how to, or have hint?
Thank you very much! smiling smiley
Re: Äuto bed leveling only once in a while
November 22, 2015 02:25PM
I think you don't fully understand auto leveling. Machines that come with auto leveling usually require releveling/zeroing with every print because they are so poorly made they can't maintain the level or zero settings from one print to the next. If you don't relevel for each print you'll be lucky to get the second print to stick to the bed well enough to finish.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Äuto bed leveling only once in a while
November 23, 2015 04:42AM
I am sorry, I have to disagree smiling smiley Cause I am the designer and builder of my machine smiling smiley
It's sturdy, and precise, I am sure that the bed doesn't move between prints, but is always, not perfectly orthogonal to other axis.
But I I know this offset, I could correct it without probing every time.
Re: Äuto bed leveling only once in a while
November 23, 2015 07:29AM
Autoleveling doesn't correct for nonorthogonal axes. Its only purpose is to correct misalignment of the bed with the XY plane so the first layer will stick. It assumes, as it has to, that the axes are orthogonal and that the bed itself is a plane.

Someone wrote some firmware that has "orthogonal axis compensation" (which should have been called "nonorthogonal axis compensation") that attempts to correct errors in orthogonality in the firmware, similar to the way that auto leveling works. You have to print an object and measure it then enter the the data into the firmware to get it to correct the errors for you. It assumes that the error remains the same at all times. If the alignment of the axes changes, such as in a machine with two motors driving two Z screws that lift the X axis, and someone turns one of the screws manually (usually as a quick way to "level" the bed!) or the mechanism binds and throws the alignment off, the compensation won't work.

If your machine is solid, it shouldn't need autoleveling. You're carrying a sensor and its wiring around on the extruder carriage, adding to the moving mass, and adding to the unreliability of the machine by throwing in more potential failure points without them providing any benefit to make them worth the risk. My machine is solid (see the link in my sig, below) and I don't have to adjust the level settings unless I change something that will affect it. The zero setting is only adjusted if I put some blue tape on the bed to print PLA and then switch back to ABS.

The solution to nonorthogonal axes is two fold. First align the axes properly, and second lock them down tight so they can't get out of alignment. I designed a test cube and wrote a spreadsheet that tells the positional adjustments to make based on measurements of the printed cube's diagonals. It will allow you to align all axes to be orthogonal. You can DL the object and the spreadsheet here: [www.youmagine.com]. You have to decide, based on your machine's architecture, which axis to use as the "reference" and which ones to move to perform the alignment. Once the axes are aligned, you want them to stay that way. If your machine has the X axis lifted by two Z axis screws, the best way to ensure it remains aligned is to use a belt to drive both screws with a single motor. That keeps them synchronized at all times and prevents having to realign the X axis by printing another test cube. I use a belt to drive the Z axis screws in my machine, and I haven't had to touch it since its final alignment was done almost a year ago.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Äuto bed leveling only once in a while
November 23, 2015 07:32AM
Quote
victorjung
I am sorry, I have to disagree smiling smiley Cause I am the designer and builder of my machine smiling smiley
It's sturdy, and precise, I am sure that the bed doesn't move between prints, but is always, not perfectly orthogonal to other axis.
But I I know this offset, I could correct it without probing every time.

RepRapFirmware allows you to put bed height corrections in the configuration file as an alternative to probing, but AFAIK Marlin doesn't.



Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Äuto bed leveling only once in a while
November 23, 2015 09:51AM
I have the same issues. I understand the limitations of marlins auto bed levelling and have dug through the code to get a feel for it. The problem I have is that it is very inconsistent. I can do consecutive g28 + g29 combinations and get variances of a mm or more. Enough that i get air prints fairly often. I can do m48 at various points around the bed and get a standard deviation of .003mm so the problem doesn't appear to be mechanical. I am currently using marlin 1.0.2 and apparently the release candidate bug fix version has some fixes in it.. I suspect the problem may be something in my routine but I certainly don't see any difference between when it works and when it doesn't.
Re: Äuto bed leveling only once in a while
November 23, 2015 10:48AM
Interesting that you say it is quite inconsistent, I've noticed that too, and have been wondering if it is mechanical. I too can get very good reproducibility from my probe. I always assumed it because my i3's bed is relatively quite a wobbly structure. Be interested to hear if you get anywhere with solving this.

Perhaps a later version of Marlin?
Re: Äuto bed leveling only once in a while
November 23, 2015 10:57AM
Ok digital dentist, my bad, I shouldn't use the word orthogonal, My axes are orthogonal I checked that and it is fine.
@DjDemonD and @Micahel Brock do you check the values?
I gonna dig in the code also, from reprap firmware check how the height corrections is done and look how it could be done in marlin
Sorry, only registered users may post in this forum.

Click here to login