Why does the MINI wait for the hotend to COOL before performing mesh auto bed leveling?
I've noticed that my Prusa MINI+ will wait for the hotend to cool before performing mesh bed leveling, which seems odd to me. I use the preheat feature on the printer while I finalise my slicing settings, just to find that when I start printing it has to wait for the hotend to cool (e.g. from 215ºC → 170ºC). Is there a good reason for this?
I note that the G-code generated by Prusa Slicer (Version 2.4.0-alpha1+x64) is using the "R" version of setting temperature:
M109 R170 ; wait for bed leveling temp
which according to the Marlin firmware docs means:
If the temperature is set with R then M109 will also wait for the temperature to go down.
I would expect it to use the "S" version which:
If the temperature is set with S then M109 waits only when heating.
Is there a reason the hotend needs to be cooled to 170ºC before mesh bed leveling? Put another way, what will go wrong if I change it from R → S?
It's a feature introduced in the startup g-code for the Mini, and i have copied it over to my Mk3S+ startup code. If you search the forum, there have been several complaints about the nozzle oozing during bed leveling and leaving little dots behind (and I have seen my share of that myself). This procedure basically cools filament down so much that oozing is avoided, while leaving filament still pliable enough not to damage the steel sheet when there's some still left hanging on the nozzle.
Ah right, thanks.
So the preheat feature is only really useful for loading filament? If so, it seems wasteful for it to also heat the bed straight away..
Amen to that
RE: Why does the MINI wait for the hotend to COOL before performing mesh auto bed leveling?
I change my startup gcode to preheat to 145 for PLA and 155 for PETG. I found these to be the max temps with no oozing. I'd like to adjust the mini's preheat to match these temps actually. When I do preheat, I then lower the nozzle to the temp above.
RE: Why does the MINI wait for the hotend to COOL before performing mesh auto bed leveling?
[...] So the preheat feature is only really useful for loading filament? If so, it seems wasteful for it to also heat the bed straight away..
Buried somewhere in these forums is a post in which it was explained that the assumption is that you're going to begin printing, so might as well warm it up. Beyond helping with bed adhesion, warming the printer and stabilizing temperatures can help with print reliability and uniformity. I let my Mk3 "warm up" before starting printing each day. You can always modify the start gcode to do things differently if you prefer. I've got some notes on doing this with the Mk3 that might be useful.
RE: Why does the MINI wait for the hotend to COOL before performing mesh auto bed leveling?
A similar irritating (at least for me) "feature" (bug?) is the time-consuming and energy-wastefulness of heating the bed when all I want to do (at the moment) is to load, unload or change the filament. Unless I'm ready to launch right into a print job, heating the bed serves no purpose except to waste my time and increase my electrical bill. This needs to change.
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RE: Why does the MINI wait for the hotend to COOL before performing mesh auto bed leveling?
There is nothing to stop you writing a gcode program to simply heat the hot end and run that instead of the LCD Option.
You could also run Gcode to eject the filament after a print, to save having to re heat to remove the filament later...
Both Versions of MMU, retract the filament to the holding position after each multimaterial print, as a matter of course...
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: Why does the MINI wait for the hotend to COOL before performing mesh auto bed leveling?
I guess my point is, why should I have to do a work-around for a firmware glitch that serves no purpose, so it's off to github.
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RE: Why does the MINI wait for the hotend to COOL before performing mesh auto bed leveling?
For the bed leveling process, it doesn't matter if the bed and nozzle are hot or cold unless you plan to only print with one set of settings. In this case, heating up to those temperatures before leveling can help to ensure your level is exact (because materials will expand), but this isn't strictly necessary.
RE: Why does the MINI wait for the hotend to COOL before performing mesh auto bed leveling?
I've ran the MK3S for years and just added a Mini to my arsenal. It is challenging to go back and forth between the MK3S and Mini when the process is so different. The MK3S preheats to a working temperature. When using the Mini, you don't want to forget a setting, or have the wrong material loaded, or get a bad first layer. If you do, it is preheat, heat, cool, preheat, cool, heat, cool etc.