Mesh Leveling Making Things Worse
Hi guys, new to Prusas but have been 3D printing for 6 years now.
Overall this new MK3 is a very nice machine, but I have noticed some weirdness with the mesh leveling (FW 3.4). I am printing a part with a very large footprint (6.5" x 6.5"), so I get to see a large amount of bed surface. The majority of the area was extruding a correct width, but some areas were under-extruding a bit, while others were over-extruding. I watched the Z screws and found that it was bringing the nozzle closer in the over-extruded areas and vice versa. Hmmm.
I designed and printed an indicator holder and checked the bed surface. I didn't find deviations that matched the areas where I watched it compensating. I made some shims and was able to mechanically level the bed to within 0.001" across all 9 sensor points. Then I tried to print the object... and again I found it to be "correcting" in a way that made things worse.
I decided to just comment out the G80 mesh leveling call and try again. The immediate observation was the live Z adjust value was suddenly way off. Why would this change, since Z still seems to be homed using the sensor during the G28 W call? I had to change the live Z adjust from -.635mm to over 1mm. I'm now worried that it will smash the nozzle into the bed if I print something with mesh leveling on, without reverting this setting.
Either way, the first layer result is far better without mesh leveling. That is a disappointment for sure.
Re: Mesh Leveling Making Things Worse
Even after the giant correction to the live Z adjust, I tried restarting a print and the nozzle was sky high again. Something about disabling mesh bed leveling seems to prevent the initial live Z adjust value from being applied. Only subsequent changes to that value, after the homing, have an effect.
Re: Mesh Leveling Making Things Worse
take the mesh bed levelling command out of your start g code.,
then simply adjust the live Z value and you should not get any compensation...
I don't know, but it is possible that the mesh values are stored in non volatile memory, if this is the case, a factory reset should clear that out
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
Re: Mesh Leveling Making Things Worse
I appreciate the reply, but it would be more helpful if you thoroughly read my post first. Your suggestion was already discussed in my first post.
It really shouldn't matter whether the last mesh values are still in EEPROM, without the G80 command, they are not applied.
Re: Mesh Leveling Making Things Worse
Hi, same problem here
I printed for a half year with my Prusa MK3 without bigger issues and now noticed that the first layer thickness is not reliabe. I get nice first layer after live adjust, i can repeat it but after some prints it drifts away. I am not sure if it was so in the beginning and i did not notice it or if it got worse recently. I would like to understand the source of the error and tried to disable the automatic leveling to see if its the source of the variations.
Tried to comment out the line as topic starter and it failed as described.
It should be easily possible to make the automatic mesh bed leveling optional? Please provide a solution.
Kind regards
Re: Mesh Leveling Making Things Worse
Yup - seen exactly the same - in fact the pinda is not sensing accurately irrespective of temperature accurately. My bed mesh indicates that the bed is higher at the back than the front by 0.7mm - in reality it is not it is only 0.3. The mesh bed matrix shows my bed to be fairly flat - it is not, the bed is actually dished, if you put a straight edge on it in any angle in the X/Y plane you see daylight in the centre of the bed- and not a small amount either it is -0.2mm referenced to the outer edges - the mesh matrix doesn't even indicate that the dish exists.
If you want to see this in action on your own machine it is fairly straightforward. Move your bed fully to the back on the Y axis, move the X so that the nozzle is over the bed, make sure there is a reasonable gap under the nozzle - not too big you need to measure it. Then get a set of simple feeler gauges and measure the gap between the nozzle tip and the bed (easiest if you get rid of the fan shroud) take care not to force the feelers, you can use a sheet of paper if you're worried about marring the bed, they should be a light drag fit - avoid pressing on the bed. Now move the Y axis only all the way to the front and repeat - measure the gap in the same way. You can do this in the same 9 points as the mesh calibration, thus you know how inaccurate the Pinda is and I know 100% that mine is inaccurate, what's more the inaccuracy is not consistent.
I think mesh bed levelling is a great idea but it only works correctly if the information it is using is correct (we call it GIGO - garbage in garbage out) it would be nice to be able to apply 'offsets' to the mesh points - to correct the Pinda error then I don't care what values it reports as long as it produces the correct and consistent results. I have tried thermal calibration of the Pinda, it didn't help.
Currently my smaller prints are 'OK', larger prints that span large areas not so much you can see clear differences in the 1st layer, this leads to poor adhesion and sometimes warpage / lifting as a result. At the front of a large print on layer 1 there are no gaps between the lines but at the back there are, something isn't right, for me this issue is a work in progress, my prints come out OK but I need to figure out what is going on as it irks me.
Re: Mesh Leveling Making Things Worse
Exact same issue here since beginning. The Mesh bed is way over compensate the uneven bed. It make the lower area print widest line and high area print thin line....the 50um max correct is far not enough to pull it back.....
Re: Mesh Leveling Making Things Worse
Has anyone figured out a way to disable mesh leveling, without losing proper live Z adjust functionality?
Re: Mesh Leveling Making Things Worse
Has anyone figured out a way to disable mesh leveling, without losing proper live Z adjust functionality?
Keeping this afloat as I too would like to be able to disable auto bed leveling. Maybe a way to disable in firmware?
Re: Mesh Leveling Making Things Worse
After chatting with support and them not being able to troubleshoot, I sent an email to [email protected] relaying these issues.
I haven't heard back yet, but I suggest everyone who reads this send them a similar email, to help it gain priority.
Re: Mesh Leveling Making Things Worse
Have you guys read up on the PINDA warmup discussion? There's a lot to it, but in short: You want to let the PINDA cool between prints, then stabilize at 35C before doing mesh bed leveling. I've not had any issues, but that may just be luck. I've build a PINDA warmup into my startup gcode.
Re: Mesh Leveling Making Things Worse
Have you guys read up on the PINDA warmup discussion? There's a lot to it, but in short: You want to let the PINDA cool between prints, then stabilize at 35C before doing mesh bed leveling. I've not had any issues, but that may just be luck. I've build a PINDA warmup into my startup gcode.
Bob I would like to read up on it... I preheat the nozzle and bed for about 5 min before I print but I did not know about the letting things cool down between prints a search on "PINDA warmup discussion" just turns up this post of yours.
Re: Mesh Leveling Making Things Worse
[...] I preheat the nozzle and bed for about 5 min before I print but I did not know about the letting things cool down between prints a search on "PINDA warmup discussion" just turns up this post of yours.
It looks like the information has been distilled into a much easier to follow wiki page. Since I tend to update firmware regularly and often do a factory reset, I've followed the procedure described under An Alternative Approach that Does Not Require Temperature Calibration in my startup gcode. This has been working well for me, with the caveat that our rapidly-cooling fall temps have prompted me to up my bed warmup temp to 65C to avoid long waits on print starts. You can see my startup gcode routine here. I've found it unnecessary to wait for the PINDA cool if I wait for my nozzle to stabilize at my no-ooze temp.
I wonder if the big temperature swings we've seen since summer might account for some of these issues?
Re: Mesh Leveling Making Things Worse
Thanks bob very interesting
Re: Mesh Leveling Making Things Worse
It is, calibrated mine using that and my first layers have improved significantly.
One thing that is also interesting to do is to make surface maps (G80, G81) at different temperatures but to do it at intervals, it is really interesting just how much impact this has - or how much impact heat soak has, ambient temperatures are a big deal for sure but so is the preheating etc.
One thing that springs to mind is that none of the occurs when the wizard is run so setting 'live Z' when the wizard wants you to is pointless.
Re: Mesh Leveling Making Things Worse
Are you using the Octoprint plugin to do this? I haven't ventured down that path yet, but realize I should. My bed is pretty level though, so I'm not in a hurry to correct anything.
[...] One thing that is also interesting to do is to make surface maps (G80, G81) at different temperatures but to do it at intervals, it is really interesting just how much impact this has - or how much impact heat soak has, ambient temperatures are a big deal for sure but so is the preheating etc.
Re: Mesh Leveling Making Things Worse
Yeh I have a full fat Pi attached via USB, I use the specific Prusa bed levelling plugin. There are a couple but only the Prusa one gets the bed the correct way around - and understands that for some reason the Prusa doesn't use standard Marlin commands for this (Prusa uses G80 and G81 vs Marlin G29)
You can still get some numbers for use in a spreadsheet if you run first G80, then run G81 via a terminal window to the printeri.e. Pronterface or Simplify3D this will give you the bed levelling numbers.
I can't run a sample off because my printers active at present, I'll try to remember and do one later.
Re: Mesh Leveling Making Things Worse
Email support was no help.
I created an issue on Github. Feel free to chime in there:
Re: Mesh Leveling Making Things Worse
Have you guys read up on the PINDA warmup discussion? There's a lot to it, but in short: You want to let the PINDA cool between prints, then stabilize at 35C before doing mesh bed leveling. I've not had any issues, but that may just be luck. I've build a PINDA warmup into my startup gcode.
It's possible that it plays a part, but I don't think that is what is going on here.
The Pinda temp shouldn't be changing much at all between points of a single mesh leveling session, yet I am seeing point to point error. The temp calibration issue should manifest as more of a global height change between different prints. You would constantly need to adjust your live Z value to chase this error around. I never have to do this. My 1st layers are very consistent in absolute height, and even in the mesh leveling errors I see.
RE: Mesh Leveling Making Things Worse
Hi everyone,
Little late to the party, but if you're still having problem this might help. I was having problem with the first layer being consistent on large footprint parts. Also if I tried to print a bunch of small parts all over the bed some would not stick. I have adjusted all three or my mk3/s with manual adjustments, no code to the point where I'm getting nice first layer across the whole heatbed. Instead of typing it all out take a look at my video. I explain what was going on and show how I fixed it.
Hope this helps,