@oliof thanks for this, it sounds quite reassuring. I'll just stick to the documentation when I have to touch any of the electronics!

@infiniteloop said in Mesh Compensation Overcompensating a bit?:

@suntoxx It’s a bit late for a comprehensive reply, but I will try my best …

Without the use of a preprocessor, I don’t know a way to automatically confine the mesh to an area used by the actual print.

Check out the Prusaslicer startcode i found last night. It works nicely! Just wish that Duet would handle it and not that you got to adjust it according to each slicer.

Maybe you could try some faster acceleration, 100 for Z looks quite moderate to me.

Z acceleration seems moderate in comparison to the other axis? What would that improve? I guess not much in terms of time. Less stringing?

Your Edits prove the value of a narrow mesh. However, mechanical precision of a printer is limited (not only by the BLTouch or the steppers), so it’s worth to take a look at first layer adhesion, too. To improve this, you could play with print speed, bed and hotend temperatures.

Yes, i am quite far up in temperature I think, using 70° and 235° for PLA for this print. I actually did have an adhesion problem too on this print, at least on some print positions. I did not know that Iso and paper is not enough. Using dishwasher or window cleaner now on top and adhesion on the king sheet is sufficient for this more difficult print.

Edit: Adjusted z by 0.01mm and result is consistent and perfect now!

@jay_s_uk yes, those 2 are in the config.g. Something like
G31 X-xx.x Y-xx.x

@fcwilt yes, it's a MK52 with the Mk-52-block carriage, with LHBB10 aluminium bearing blocks.

@fcwilt thanks for the response! It seems the print that failed before the problem appeared, left a small blob of filament on the tip of the nozzle and that interfered with the BLToch, because the BLTouch had moved up a tiny bit.

@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

@fcwilt ah, damn, i missed that all the way up there to the right. The disadvantage of 43" screens Thanks!

Do you by any chance know how to use the Echo command to create a macro?

@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.

@infiniteloop said in Mesh Compensation Overcompensating a bit?:

You can lower the limit to any value you find reasonable for your printer. As long as you supply reliable data from the mesh, you don’t risk to damage either nozzle, print bed, or both. To be safe, you could lower the Z limit only for the time of a print - else, you might ram the head into the bed with DWC’s machine movement controls.

Reasonable would be the lowest number necessary, wouldn't it? I have done quite a bit of testing and can't seem to find any confirmation of this working. Is there any documentation about this or has one of the responsible coders mentioned this? (is this compensation reprap oder duet3d code?)

The thing is that i haven't found any indication yet, that lowering the limit down to -4 has any effect and the keychain already has strong visual changes at about 0.02mm change on z. Neither does it seem to affect adhesion on the lower parts of the bed on normal prints.

@infiniteloop said in Mesh Compensation Overcompensating a bit?:

For you: a problem, for others: a feature to get a uniform surface

Well, it does help a lot up to .1mm deviation

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.

I would have expected that G29 already permits it and only as much as is necessary for the bed in question. Or is there a reason why you trust your probe to compensate convex parts of your bed, but not concave ones? Is the risk higher?

Do you have to lower the limit by the amount of bed deviation to compensate (-0.340mm in my case) or do you also have to take the G31 z probe offset or anything else into account?

The need for a heightmap itself proofs the existence of a, let’s say: less than perfect bed.

That's one way to put it. It sucks would describe my bed with .5mm deviation well too though, I suppose

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.

The filaprint precision bed unfortunately won't work with my printer. I guess I will try the silicone mod for prusa mk3s+ and see how that improves things. It's a shame. The printer can handle those tight tolerances without breaking a sweat and with a better bed he could do it across the entire print surface. Lets hope the mod can get most of the bed below .1mm deviation.

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?

@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.

@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.

@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

@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

@blacksheep99 yes, they are two sided.

@fcwilt yes, it's a MK52 with the Mk-52-block carriage, with LHBB10 aluminium bearing blocks.

@fcwilt it must be this one https://www.prusa3d.com/product/magnetic-heatbed-mk52-24v-assembly/