First layer calibration Question  

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keith.g5
(@keith-g5)
Eminent Member

Hello all.

In my MK/3-MK/3S upgrade I would like to know what the thickness measurement of the First layer calibration should be.

We've all seen the photos and graphic images in the handbooks that describe the proper settings.

I want to measure the sample so I can get it exactly right every time. I have plenty of micrometers so that's not a problem.

When I do mic it mine generally measure ,02 to ,023 mm. Is that correct?

thanks

Posted : 28/07/2019 9:20 pm
Tim
(@tim-m30)
Illustrious Member

Layer 1 when set to 0.200 mm should be ... wait for it ... ta-da! 0.200 mm.

Otherwise you will have a height error in your parts: a 25 mm cube will be +/- whatever layer 1 error you actually have.

That said, most of us adjust layer 1 to get a good contact patch, welded extrusion strips, and generally a good looking layer 1.   And all this is moot if you are using a textured sheet, except for the "pretty" parts.  

 

ps: that all said, mesh level adjusts layer 1 nozzle position to compensate for variations in apparent bed flatness. So you will get some height error anyway.  And mesh level isn't perfect, interpolations used are 'tweaked' and may even add some error, especially outside cal points. So ... experiment and use what works best for you.  I started by trying to keep layer 1 exactly 0.2 mm ... eventually gave up.

This post was modified 10 months ago by Tim
It is always wise to get more than one opinion......
Posted : 28/07/2019 9:49 pm
david.a66 liked
keith.g5
(@keith-g5)
Eminent Member

Thanks for the reply Tim. I understand your point about layer resolution. I do print 25mm cubes/boxes to confirm dimensional accuracy in x/y/z axis.  I'm just wondering what the measured thickness of the calibration sample. See photo below. Oh, as a correction I miss-typed the dimensions in my first post. Should be; 0,2 0,23. Oops.

Posted : 29/07/2019 2:58 pm
Tim
(@tim-m30)
Illustrious Member

That isn't really a valid sample...  the patch is too small and never where it needs to be, like where we actually print.

And thickness might best be 0.156 one print, 0.241 the next.  "About" 0.200 is the best most can do since the bed isn't perfectly flat, and the mesh level code isn't 100% repeatable because every different start temperature changes PINDA accuracy/sensitivity.

Cal Circles.zip

 

As for a real number, 0.2 mm or whatever this is set to is the ideal: 

... but it's often not the optimal choice. Just too many subjective and just as many unavoidable variables. Is filament actually 1.750 mm? Is the nozzle perfectly aligned and perpendicular to the bed?  Is the bed perfectly level across the print area? What is heat doing to reshape the bed while I am calibrating?  How does the heat affect the precision of the height detection? Did the filament diameter change between start and finish?  Did the extruder shift when changing directions?  Is the nozzle actually true and perfectly flat or is there a small angle that produces more plastic when traveling 67.4 degrees? Or do the belt notches cause a micro stutter that causes variations in the extrusion height and width as the extruder moves?

 

It is always wise to get more than one opinion......
Posted : 30/07/2019 2:20 am
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