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Active Leveling Too Close

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Sorry if this is in the wrong section. Not sure if it's an active level calibration issue, or simply a setting in Cura.

When I active level, my 1st layer is too close. I resolve this by lowering the bed some by tightening the bed screws as the first layer prints.

My question is what is the correct way to resolve this? Printer setting or adjust this in a Cura profile? Goal is to not have to manually lower the bed. If I active level again, I'm back to square one.

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Using the cura default profile with an initial layer of .27. Non Ultimaker PLA. You can hopefully see the differences in this image and how it improves once I lower the bed. The rest of the layers are great once I get past the first layer. The lowest layer is squished more and is wider than the rest of the layers above it. Really want to dial this in and want to adjust the correct settings as the rest of the print looks great. Thank you for the assistance.

5a3327447fd61_ScreenShot2017-02-13at2_08_31PM.thumb.png.578f929d72494dec5e6a5a6173e66ab0.png

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Thanks for your picture. I'm afraid there is no way to adjust this automatically.

I'm not aware of any offsets in Active leveling.

The Active Leveling system measures pretty accurate, with standard deviation of up to 30mu, mostly less. This means that there is a 95% chance that the distance between the nozzle and your bed during the first layer is 0.27mm +/- 0.060mm. This holds for the 3 probing positions. Outside these positions, there's other tolerances like unflatness of the build plate, bent shafts, etc.

These tolerances are exactly why the first layer is usually thicker than the rest of the print: this gives some robustness against these tolerances.

We did a lot of testing by printing 3mm high hollow cylinders on the probing points, and measuring those with a caliper. That is how we came to the standard deviation of 30mu (so it includes our caliper measurement error).

Would you be able to indicate how much you adjust the height?

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Sorry... I didn't really keep track of how much I adjusted the screws for the bed. I'm guessing a quarter turn at most.

I'm assuming there is a way to inject maybe some offset in the gcode file after sliced? If so, I will re active level and play with some various values in the gcode. I will research the way to adjust the gcode or if you have the answer handy, please let me know.

But just wanted to confirm this is not a material issue or something I can overcome in a Cura setting? Thanks for your patience. Fairly new to 3D printing. Worked with CNC carvers in the past.

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Did a new manual level to get the bed back in check. And then an active leveling. Default I got this:

5a33274d25739_ScreenShot2017-02-14at1_02_42PM.thumb.png.ad4b1e0206a6e621cf8254a241a26333.png

5a33274d581ff_ScreenShot2017-02-14at1_03_01PM.thumb.png.6770e42109a3bcd254b943c088d003d8.png

Raised the bed up .1mm with "G92 Z-.1" and seems much better:

5a33274d7eeaf_ScreenShot2017-02-14at1_07_48PM.thumb.png.2673f02b104e7cbf5dbe0c6e4c1d8e7e.png

5a33274db05bf_ScreenShot2017-02-14at1_10_07PM.thumb.png.db6b42201fb1a1fa8107b78dc6506a3b.png

will play with it more to see how it affects adhesion, etc.

5a33274d25739_ScreenShot2017-02-14at1_02_42PM.thumb.png.ad4b1e0206a6e621cf8254a241a26333.png

5a33274d581ff_ScreenShot2017-02-14at1_03_01PM.thumb.png.6770e42109a3bcd254b943c088d003d8.png

5a33274d7eeaf_ScreenShot2017-02-14at1_07_48PM.thumb.png.2673f02b104e7cbf5dbe0c6e4c1d8e7e.png

5a33274db05bf_ScreenShot2017-02-14at1_10_07PM.thumb.png.db6b42201fb1a1fa8107b78dc6506a3b.png

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I had exactly the same problem with my UM3, and on top, the prints just couldn't be removed from the plate without breaking them.

G92 Z-0.1 did the trick!!

Strange that we can not dial this in somewhere in the print settings.

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Glad it helped. I still haven't a smooth solution to overcome this. I either just live with the first layer being too close in exchange for being able to print directly to the printer over the network. Or if I want a nice looking first layer, I use the USB drive to transfer the file after I add the G92 offset. It's too bad that I have to do a workaround like this. It would be great if the printer had an ability to adjust this offset in the firmware or Cura.

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Hi

I wanted to revive this topic and see if we can get momentum going for some sort of firmware mod to allow 'Active Leveling Offset Input'. After manual leveling, my first layer thickness is spot on at about 0.27mm, but as soon as I perform an active leveling, all other settings the same, the first layer thickness measures about 0.12-0.14mm with calipers.

I'm seeing consistency in these measurements when I repeat the process, which gives me hope that the leveling sensor is as accurate as Ultimaker has touted, however I strongly believe there needs to be an offset allowance in the build plate leveling menu to correct for machine-to-machine variances.

Any thoughts on this from the community or from Ultimaker?

Thanks

Jeff

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I'm stilll puzzled by this problem, but I have an idea. When we updated the active leveling fw in December, it was thoroughly tested. The test objects that should be 3mm high were measured to be like 2.95 mm on average. Really close to 3. Tested on multiple printers of course.

But I think we overlooked one thing: when printing these test objects over and over again, the glass plate never cooled down.

In a recent experiment, we focused on the dimensional effects of heating up the printer. These were significant, as can be expected. However, the time constant I found surprisingly high. Distance between nozzle and print bed stabilize only after 10-15 minutes or so.

So @Jeffg1, maybe you want to try the following: preheat your print bed for at least 20 minutes and then start active leveling. Is then the first layer thickness what you expect?

.

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So @Jeffg1, maybe you want to try the following: preheat your print bed for at least 20 minutes and then start active leveling. Is then the first layer thickness what you expect?

I have been following this as I was curious. But tomnagel's reply makes sense to me.

I do not experience that, but, as I change plates, clean and other things, I am doing a pre-heat just to cut down time. So, this would explain why I do not get this as I do the leveling after all that time doing other things.

Edited by Guest

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In Cura 2.5 the software does not give you the ability to modify machine settings, such as adding a line of Gcode to create a Z offset.  Unless there is some other way to accomplish this?

 

I just noticed (maybe it's been there a while) that I can now add start and end gcode in machine settings for my UM3 - Cura 2.6 stable. I added the G92 command to the start gcode and verified it's inserting it in.

I still need to play with preheating more as Tom suggested... but now with the start gcode option I can inject the G92 command into the normal workflow and print over the network. This will be great as now I can slice and print over the network and insert G92 if needed vs having to manually manipulate the gcode file after the fact, put on USB, etc.

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I can say that in certain situations that it would be easier to do in Cura or firmware so that you could accommodate filaments that 'want' to be printed round and not flattened such as T-Glase as that helps with transparency.

For the time being I do a manual for that and skip the active leveling so I can create that offset, but it is not as accurate as inputting direct numbers.

Edited by Guest

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I'm stilll puzzled by this problem, but I have an idea. When we updated the active leveling fw in December, it was thoroughly tested. The test objects that should be 3mm high were measured to be like 2.95 mm on average. Really close to 3. Tested on multiple printers of course.

But I think we overlooked one thing: when printing these test objects over and over again, the glass plate never cooled down.

In a recent experiment, we focused on the dimensional effects of heating up the printer.  These were significant, as can be expected. However, the time constant I found surprisingly high. Distance between nozzle and print bed stabilize only after 10-15 minutes or so.

So @Jeffg1, maybe you want to try the following: preheat your print bed for at least 20 minutes and then start active leveling. Is then the first layer thickness what you expect?

.

 

I pre heated the printer for 15 minutes, active leveled again, pre heated for a another :10 and then printed. It still appears to be too close for me. I will do this procedure a few more times as I print in the future to see if I notice any difference.

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I finally had the time to put together some tests.  In all cases, the Cura initial layer height is set to 0.27mm.  In all cases a 2-line skirt was printed and used for measurements with digital calipers.

1.  Preheat 30" and then run active level:  Thickness 0.16mm

2.  Cool off 1 hour and then run active level:  ~0.15mm

3.  Manual level cold, using Ultimaker calibration card (0.10mm thick):  0.10mm

4.  Manual level cold, using business card (0.22mm thick):  0.26mm

Since manual level & active level are both producing 1st layer thickness that is smaller than the Gcode is calling for, I think there is some sort of software error where the printer thinks the nozzle is farther from the glass than it actually is.  

So if I wanted to add a G92 command to the start code for my machine to move the plate away from the nozzle by 0.10mm, would I enter this line:

G92 Z0.1

or

G92 Z-0.1?

Thanks

Edited by Guest

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Thanks for sharing your results. It's not what I expected, I expected a bigger difference between cold active leveling, and hot active leveling.

I think you run active leveling separate from your print job. It is slightly better to run it as part of your printjob, because then the inaccuracy influence from the z-home sensor is cancelled. (standard deviation around 10mu).

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You can't do a G92 by itself.  It matters where the bed is at the moment you do the command.  so for example you could do:

G0 Z10

G92 Z10.1

That would move the bed so the nozzles is 10mm above the bed but then tell the printer it is actually at position 10.1 such that when it goes to position 0 it will press somewhat into the glass.  Or

G0 Z10

G92 Z9.9

In this case when it goes to Z0 it would hover .1mm above the glass.

Or you can do as you said:

G0 Z0

G92 Z.1  

Be careful at Z0 as you can hit a clip.  This will press more into the glass.

G0 Z0

G92 Z-0.1

This will make the head hover a little higher above the glass when printing.

Edited by Guest
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I seem to having the same issue. I see 'waves' or 'ripples' in my first layer. Similar to the last picture here: https://ultimaker.com/en/community/34262-pla-ripples

If I manually turn the bed screws a bit (about a half or quarter turn) those waves disappear.

So do I add the following to the start code to try to fix this?

G0 Z10

G92 Z9.9

In this case when it goes to Z0 it would hover .1mm above the glass.

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I tried this out and it works like a charm. The left object is without the extra start gcode and has many waves in the first layer, the right object is with the small z-height adjustment:

20170729_083236.thumb.jpg.a21f841cf6a916041462265fa5879d57.jpg

 

I seem to having the same issue. I see 'waves' or 'ripples' in my first layer. Similar to the last picture here: https://ultimaker.com/en/community/34262-pla-ripples

If I manually turn the bed screws a bit (about a half or quarter turn) those waves disappear.

So do I add the following to the start code to try to fix this?

 

G0 Z10

G92 Z9.9

In this case when it goes to Z0 it would hover .1mm above the glass.

 

 

20170729_083236.thumb.jpg.a21f841cf6a916041462265fa5879d57.jpg

Edited by Guest

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