Mesh Compensation Overcompensating a bit?
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@fcwilt said in Mesh Compensation Overcompensating a bit?:
What about you current bed prevents it from being leveled?
Taking it apart and readjusting it every once in a while. Or is there a more permanent solution than the Nylock mod.
@fcwilt said in Mesh Compensation Overcompensating a bit?:
Can you elaborate a bit?
If the probed coordinates would be used as absolute values at those exact coordinates, they should be perfect in regard to z offset, getting more imperfect (on average) the further away from the probed point. The squished keychain i think proves this right.
Is there a way to set a "per stl" z offset? The keychains itself seem fairly uniform.
@stephen6309 said in Mesh Compensation Overcompensating a bit?:
@suntoxx Have you a low mesh compenstaion taper?
https://docs.duet3d.com/User_manual/Reference/Gcodes#m376-set-bed-compensation-taperNever heard of it, going to look at it, thanks.
Edit: If i understand it correctly, I would need the opposite of this command. For depths instead of height.
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@suntoxx said in Mesh Compensation Overcompensating a bit?:
Taking it apart and readjusting it every once in a while. Or is there a more permanent solution than the Nylock mod.
Aside from my one printer with three Z steppers allowing for Auto Bed Leveling my other printers have 3 or 4 "thumbscrews" that can easily be adjusted use the Manual Bed Leveling Assistant the is built into the firmware
If the probed coordinates would be used as absolute values at those exact coordinates, they should be perfect in regard to z offset, getting more imperfect (on average) the further away from the probed point. The squished keychain i think proves this right.
Which is why I use that max number of probe points to restrict the amount of interpolation the firmware needs to do to determine the Z adjustment between probe points.
What is your bed made out of? Perhaps you could replace it with something flatter.
Frederick
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@fcwilt it seems to be the standard Prusa mk3s heatbed.
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@suntoxx said in Mesh Compensation Overcompensating a bit?:
@fcwilt it seems to be the standard Prusa mk3s heatbed.
I know nothing about that printer - I will see what I can find out. Some companies make upgraded parts for popular printers.
Frederick
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@fcwilt it must be this one https://www.prusa3d.com/product/magnetic-heatbed-mk52-24v-assembly/
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@suntoxx said in Mesh Compensation Overcompensating a bit?:
@fcwilt it must be this one https://www.prusa3d.com/product/magnetic-heatbed-mk52-24v-assembly/
So that is the one you currently have on your printer?
Frederick
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@fcwilt yes, it's a MK52 with the Mk-52-block carriage, with LHBB10 aluminium bearing blocks.
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@suntoxx Do you have to print them face down? I know that doesn't deal with the problem you're discussing.
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@blacksheep99 yes, they are two sided.
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@suntoxx Understood. I can't add much help to your issue. I did wonder if a smaller nozzle may help you achieve what you want.
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@blacksheep99 i tried a .25 nozzle and it did work much better, but I had warping issues with this keychain size. A slightly smaler size did print very nicely though. Unfortunately i need this size. I could try it again though, as when I had the warping issues, I wasn't aware yet, that cleaning with iso and a shiny and clean surface, don't necessarily mean perfect adhesion. Now that i also use windex and water on top, adhesion is stronger. But i got most of the keychains printed already. I would still like to solve this problem though. Looking at a filafarm precision bed atm, but not sure if I can use that on a caribou.
And a little update: I got a 8x9cm surface area, that is close to perfect, and i can print 2 perfect keychains simultaneously on it
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@suntoxx said in Mesh Compensation Overcompensating a bit?:
And a little update: I got a 8x9cm surface area, that is close to perfect, and i can print 2 perfect keychains simultaneously on it
I'm sure you recall that the more grid points you specify (max 21 by 21) the better the firmware can correct the Z position during printing
Frederick
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@fcwilt yes, but on the rest of the bed, even 441 is not enough to print more than one at a time. On this part of the bed, 49 points gives a close to perfect result for two keychains at once. It's pretty much the center of the bed.
So it appears to me that something around 0.1mm deviation is more less the limit of what the mesh compensation can handle, if you expect more than adhesion.
Edit:"not enough" i meant
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@suntoxx said in Mesh Compensation Overcompensating a bit?:
So it appears to me that something around 0.1mm deviation is more less the limit of what the mesh compensation can handle, if you expect more than adhesion.
Not sure what you mean. There is no such limit that I am aware of.
But it is certainly true that since the process interpolates between gird points that the bed can have deviation between those points that the firmware will not be aware off.
Perhaps by using the max number of grid points you can find a size of grid that can print more than 2 items.
Frederick
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@fcwilt the z offset only works as good as I need it to be in this project, for a narrow margin of heights. Unfortunately this 8x9cm area in the middle of my bed seems to be the only area with a suitable height range. There i got maximum deviations of about 0.1mm and i can print two instead of one of the qr code keychains. I identified its coords via a P21 heightmap.
That's why i was looking at the precision bed from Filafarm, which is supposed to have around 0.05 deviations. When it's no problem to just level down and squish the unevenness away, it's ok. But if i want to maintain the perfect look of the .3mm extrusion width lines, it's a different matter, as I have to maintain a positive offset. On the center of my bed, for the 2 keychains, I now use 0.01 offset.
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@suntoxx said in Mesh Compensation Overcompensating a bit?:
@fcwilt the z offset only works as good as I need it to be in this project, for a narrow margin of heights. Unfortunately this 8x9cm area in the middle of my bed seems to be the only area with a suitable height range. There i got maximum deviations of about 0.1mm and i can print two instead of one of the qr code keychains. I identified its coords via a P21 heightmap.
I have tested Mesh Compensation with a heightmap I created by hand. It was perfectly flat on the Y axis but on the X axis the deviation ranged from 0 on the min end of the axis to 100mm on the max side of the axis.
The firmware correctly adjusted the Z axis despite the extreme deviation.
I don't know why it doesn't seem to be working well with your printer.
That's why i was looking at the precision bed from Filafarm, which is supposed to have around 0.05 deviations. When it's no problem to just level down and squish the unevenness away, it's ok. But if i want to maintain the perfect look of the .3mm extrusion width lines, it's a different matter, as I have to maintain a positive offset. On the center of my bed, for the 2 keychains, I now use 0.01 offset.
A replacement bed sounds like a grand idea.
Frederick
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@fcwilt said in Mesh Compensation Overcompensating a bit?:
A replacement bed sounds like a grand idea.
Yes, I wrote to Filaprint and will see what amount of money and effort this would take and then I will decide wether to do it or not. The numbers i print now i can do with printing two at a time, so for now I am not forced to do it. I also preordered the Prusa XL, so if i can wait until then, the possibility to switch nozzle sizes in prints will probably make quite a difference for this too.
And as much as I complain about the mesh compensation, even in my "sweet spot" where i can print two at the same time, i got 0.1mm deviation. Without the compensation, i probably wouldnt even there get the result i do now.
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@suntoxx a couple of extra thoughts for you from my experiences with mesh comp...
First obvious question is have you double checked that mesh compensation is active during the print? I appreciate its a silly question, but a stray M561 has sent me nuts before...
What is your min z height allowed in config? You'll need to allow a small negative amount so that it can reach the low points on your bed.
Have you checked that the BLTouch trigger height is consistent across the bed? Could be that any small gantry sag/tilt could be affecting it in some areas? Even just the eight of the wiring and filament feed could flex things a few micron. One option for testing this is to manually edit a heightmap in excel to make it compensate more in the areas you are seeing issues. There's a couple of bed levelling stls on thingiverse that work quite well for this kind of thing
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One thing I am wondering. When you guys say that you always get a perfect first layer and don't understand why it doesn't work for me, do we mean the same thing? That means, can you level your nozzle to the bed so that at its G31 value, it is set to z 0 (=touching the bed without a paper in between) and then always print a perfect layer on a bed (that has a bad of about .5 deviance or so), without using a z probe offset (ie with m290 at 0 and not changing G31)?
Because my problem is not that i am not able to squish irregularities out of the first layer with a negative z probe offset, the problem is that with a negative z offset, the first layer does not perfectly maintain the extrusion width, which negatively affects the QR Code embedded into the first layer. Which I believe is probably a major difference. I got the impression, that on a bed with more than .1mm deviation, you can not perfectly maintain the extrusion width on the first layer of a print with multiple colors on the first layer.
@engikeneer said in Mesh Compensation Overcompensating a bit?:
@suntoxx a couple of extra thoughts for you from my experiences with mesh comp...
First obvious question is have you double checked that mesh compensation is active during the print? I appreciate its a silly question, but a stray M561 has sent me nuts before...
Yes, it's working. Only got M561 in my leveling macro and and got G29 in my startcode.
What is your min z height allowed in config? You'll need to allow a small negative amount so that it can reach the low points on your bed.
I have tried down to -4, but various first layer prints showed no difference between 0, -2 and -4. Would't it be a strange thing if the programmers allowed the mesh compensation to end at 0, when most of its job is to compensate below 0?
Have you checked that the BLTouch trigger height is consistent across the bed? Could be that any small gantry sag/tilt could be affecting it in some areas? Even just the eight of the wiring and filament feed could flex things a few micron. One option for testing this is to manually edit a heightmap in excel to make it compensate more in the areas you are seeing issues. There's a couple of bed levelling stls on thingiverse that work quite well for this kind of thing
I believe this shouldnt be a problem. It is a CaribouDuet with 10mm Misumi rods, carriage has LHBB10 aluminium bearing blocks and Igus energy chains. Printer came preassembled and calibrated.
Also, there are no signs of tolerances. If I optimize somethingto print in one place of the bed, it reproduces it there without any variance.
However, as some of the keychains themselves, when copied around the bed, seem fairly consistent, an offset for each of them might actually improve the performance of the mesh compensation, I believe. But manually editing the heigtmap won't proof that the printer is at fault, will it?
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When you guys say that you always get a perfect first layer …
Perfect is relative. Your keychain needs extreme accuracy in order to keep the QR code readable. Most things we print are less demanding (with respect to the first layer); as long as we don’t diagnose elephant feet or air prints, we are fine. Of course, that's relative, too
squish irregularities out of the first layer
For you: a problem, for others: a feature to get a uniform surface
Would't it be a strange thing if the programmers allowed the mesh compensation to end at 0, when most of its job is to compensate below 0?
Think of the axes limits as safeguard to protect our hardware. That’s why they are absolute. If you want to exceed the limits, you have to actively permit it.
But manually editing the heigtmap won't proof that the printer is at fault, will it?
The need for a heightmap itself proofs the existence of a, let’s say: less than perfect bed. If manual editing is needed on top, I would talk of a major mechanical problem.
However, your keychains are really special - to repeat myself: you are pushing the limits. In such a situation, it’s absolutely fine to try all tricks you can imagine. The alternative would be to buy a printer in the range of 10k bucks or so, and even that will not be perfect without tweaks.
