Simple Metal Heated bed - first layer uneven across the bed?

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Simple Metal Heated bed - first layer uneven across the bed?

Postby inertianinja » 2015-Feb-Sun-19-Feb

(edited as I understand the problem better now)

I just got my heated bed upgrade, and I have been experimenting with ABS.]

The printer is not compensating (or compensating incorrectly) when auto-leveling.

As a result, lines on the left side of the bed are not being squished properly and are not adhering.
It's bad enough that the lines are actually not touching each other on the right side of the bed.

G29 in Repetier gives the results Z1.22, Z1.11, Z1.06.
G29 in Cura gives the results Z1.16, Z1.04, Z0.98

These results fluctuate slightly depending on how long the bed has been heating; I assume due to expansion.

I watched the Z-axis screw - As the print moves from X0 --> X150 (left to right), the Z axis moves up slightly.

Is it over-compensating? compensating backwards? Auto-leveling never gave me problems with the original bed.

What's going on?
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Simple Metal Heated bed - first layer uneven across the bed?

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Re: Simple Metal Heated bed - first layer uneven across the

Postby teicher » 2015-Feb-Sun-21-Feb

G29 output looks OK, I'm sure you'd see the same kind of fluctuation within the same tool if you kept repeating the test.

Lets get a handle on how the bed looks outside those three points. Can you run this gcode and report back the Z measurements? It'll just probe the 4 corners and the middle, that'll give us a quick idea of the overall level and flatness of the bed.

Code: Select all
G28
G0 X10 Y140
G30
G0 X10 Y10
G30
G0 X70 Y70
G30
G0 X140 Y140
G30
G0 X140 Y10
G30
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Re: Simple Metal Heated bed - first layer uneven across the

Postby inertianinja » 2015-Feb-Sun-21-Feb

Thanks for helping. In the interim I did a ton of searching (others have had this problem).
I went ahead and re-calibrated my Z-height and probe height (I had not done a full recalibration since I got the heated bed).

With everything fully heated up, G29 got me 0.76, 0.71, 0.71.

Calibration cube printed a nice, even first layer.
I started a print that went diagonally across the entire X and Y axes, and it was BETTER but not PERFECT.
Still not laying down evenly - still uneven enough for inconsistent adhesion.

Bed is cold now, but here are the values you asked for:
G28 - 0.88
X10 Y140 - 0.98
X10 Y10 - 0.86
X70 Y70 - 0.88
X140 Y140 - 0.84
X140 Y10 - 0.87
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Re: Simple Metal Heated bed - first layer uneven across the

Postby teicher » 2015-Feb-Sun-21-Feb

Yeah, you need to recalibrate the z offset everytime you do somethign with the bed or probe. I failed to do that step once when I was in a hurry and I have a nice little scratch on my mic6 to remind me of that.

The back left corner (X10, Y140) is just a bit different from the rest, I wonder if you could get that adjusted to be more in line with the others.

Since this is a recent upgrade, have you tried using PLA and see if you can match the print quality on this new bed that you used to get with the old?
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Re: Simple Metal Heated bed - first layer uneven across the

Postby inertianinja » 2015-Feb-Sun-22-Feb

teicher wrote:Yeah, you need to recalibrate the z offset everytime you do somethign with the bed or probe. I failed to do that step once when I was in a hurry and I have a nice little scratch on my mic6 to remind me of that.

The back left corner (X10, Y140) is just a bit different from the rest, I wonder if you could get that adjusted to be more in line with the others.

Since this is a recent upgrade, have you tried using PLA and see if you can match the print quality on this new bed that you used to get with the old?


Well ironically enough I got the bed because I was getting crappy PLA prints. My original bed was warped, which took a long time to diagnose because i had no prior experience with 3D printing. You can read about that saga in my prior threads :)

I am still trying to get to a point of good calibration so I have a baseline. Sadly I've been playing whack a mole with problems for the last month. I'm close now though. Hopefully this will be the last hardware issue, then I can move on to tweaking other settings for higher quality.
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Re: Simple Metal Heated bed - first layer uneven across the

Postby inertianinja » 2015-Feb-Mon-21-Feb

Does anyone have any suggestions for this? I would really like to get this dealt with.
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Re: Simple Metal Heated bed - first layer uneven across the

Postby evanalmighty » 2015-Feb-Mon-22-Feb

I think it has already been said, but my advice is to level the bed manually and get rid of the auto leveling altogether. IMO Printrbot took a big step in the wrong direction with their half @ssed attempt to implement this feature.
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Re: Simple Metal Heated bed - first layer uneven across the

Postby thawkins » 2015-Feb-Mon-22-Feb

evanalmighty wrote:I think it has already been said, but my advice is to level the bed manually and get rid of the auto leveling altogether. IMO Printrbot took a big step in the wrong direction with their half @ssed attempt to implement this feature.


That and the instructions are wrong.

The startup sequence in the start gcode needs to be

G28 X0 Y0
G28 Z0
G29

Or

G28
G29

Not

G28 X0 Y0
G29

As confirmed by the guy who wrote the autoleveling code. The sequence that printrbot advises does not correctly initialise the z0 plane in the center of the bed, which is used as a refference point for all z probing operations.

There is a known bug in the marlin used by printrbot in that it miscalculates the normal vector for the bed, when the bed is already close to level, this results in inaccurate calculatoin of the leveling corrections.
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225mm x 200mm - Heated Bed
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-------------------------------
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230mmx360mm bed
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Re: Simple Metal Heated bed - first layer uneven across the

Postby evanalmighty » 2015-Feb-Tue-19-Feb

I gave this same advice to a guy on Google+. Then Brook D. chimed in and told the guy it should be
G28 X0 Y0
G29

I just left it at that.

thawkins wrote:
evanalmighty wrote:I think it has already been said, but my advice is to level the bed manually and get rid of the auto leveling altogether. IMO Printrbot took a big step in the wrong direction with their half @ssed attempt to implement this feature.


That and the instructions are wrong.

The startup sequence in the start gcode needs to be

G28 X0 Y0
G28 Z0
G29

Or

G28
G29

Not

G28 X0 Y0
G29

As confirmed by the guy who wrote the autoleveling code. The sequence that printrbot advises does not correctly initialise the z0 plane in the center of the bed, which is used as a refference point for all z probing operations.

There is a known bug in the marlin used by printrbot in that it miscalculates the normal vector for the bed, when the bed is already close to level, this results in inaccurate calculatoin of the leveling corrections.
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Re: Simple Metal Heated bed - first layer uneven across the

Postby inertianinja » 2015-Feb-Tue-20-Feb

I have always had it that way, actually.

In Cura, I have this:

M104 S{print_temperature}
G21 ;metric values
G90 ;absolute positioning
M82 ;set extruder to absolute mode
M107 ;start with the fan off
G28 X0 Y0
G28 Z0
G29
M109 S{print_temperature} ;wait on temperature line
G92 E0 ;zero the extruded length
G1 F{travel_speed}

Today I went through some more tweaking of lots of things, and I'm still consistently having this problem. filament on the left side of the bed is going down flatter than the right.
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Re: Simple Metal Heated bed - first layer uneven across the

Postby Chris Knowlton » 2015-May-Sun-18-May

So were you ever able to get this corrected? I too have this problem. After a lot of successful prints, one day the right side of the first layer started printing wider than the left. My "0" and "triggered" set points all work as intended, and the Z motor turns slightly as I print the first layer, but the auto level does not correctly adjust for the little my bed is out of level.

Chris
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