Currently, I print a lot of stuff using the same material.
it’s connected to the left extruder (directly, not via AMS) and it has not been removed for a while and the printer has been turned on all the time so the printer must know exactly that the same filament was there all the time.
It’s not possible the filament would have secretly been changed without the printer noticing.
But still, at the beginning of each print it does “changing filament” and then flow calibration. Means a lot of wasted time and pointless extruded poop.
@BambuLab, can you please get that fixed in the firmware?
The options with flow calibration (set to auto mode) even say that it will only run if it hasn’t been running recently. But it still does it in auto mode. Every time.
No need to purge filament if it hasn’t changed, no need to do a flow calibration.
Or is it just that Bambu printers have the reputation of constantly pooping and Bambu is afraid they will loose the reputation if it doesn’t poop at least once during each print?
That would introduce problem, more problem than it solves actually.
It can’t actually know the filament is unchanged
Even if you never touched the spool, the printer has no physical way to verify that. Someone could have swapped to a “similar” filament, put the same brand/type back, or changed nozzle or hotend parts. Skipping purge and flow calibration on the assumption that nothing changed is asking for invisible flow errors and inconsistent print quality.
Filament and nozzle condition change over time
A spool that sits loaded for days or weeks can absorb moisture, become more brittle, or develop a slightly deformed tip in the hotend. The nozzle can also accumulate residue. If the printer skips purge and flow calibration after long idle periods, you risk poor first-layer adhesion, under-extrusion, or blobs caused by old material clearing out during the print instead of in a controlled purge.
Support and reliability would get worse, not better
The more “magic state” the firmware relies on (“trust me, it’s the same filament”), the harder it becomes to debug problems. Users will disable purging and calibration, forget they did, and then blame the printer for banding, gaps, or weak parts. From a support and firmware-design perspective, a deterministic, always-safe procedure is much easier to maintain than a conditional shortcut based on assumptions about what the user hasn’t changed.
Fact user is changing filament without using supplied ui, is not every others users issue, and should not mean every other user wastes money and time. Never had these issue on printer that has never done a purge between prints. So again not valid argument. Also, if time is issue, , the system can use timestamp from last change and do change every 3 days.
Again a simple timestamp will fix this, with 3 day limit.
Not a valid argument you can already disable number of calibrations, this would be no different.
Finally a simple warning could be displayed each print if skip changing is selected.
You have a minor point about the flow calibrations every single print from the same spool but you absolutely want to purge. Measure the length of the nozzle from the tip to the heatbrake cold zone. Cylinder volume is pi x d^2 x h. Your d is 1.75mm and h is your measurement. You want to purge at the very least this amount, every time. Maybe you can weigh the result that you think is too much and compare to this value, and make a more nuanced argument about the amount. You don’t want reheated plastic especially at the start of extrusions and even more especially at the start of prints.
Thanks, I already found this in the meantime and I created two printer profiles, with and without purge/unload.
Still, it does the flow dynamics calibration when set to “automatic” even the setting in Bambu Studio is described in a way that it should not do it:
If the printer is turned on all the time there is no way (that I know) that a user can change a filament without the printer knowing.
So according to the description it should not do flow dynamic calibration every time. Need to check it a bit closer but it could be that it only skips it for RFID filament.
Not entirely true. When your external spool reaches the end, and you immediately feed the new filament before it hits the runout sensor, it will not know the filament changed.
When you are running from the AMS and the spool runs out, the AMS will detect the runout, but also here, if you load a new spool in the same position before the runout sensor is triggered, the AMS will push the newly loaded roll against the end of the previously loaded filament. The printer just keeps running and will not pause, giving a smooth transition between 2 rolls of filament.
But you could just as easily loaded a different filament then.
And also other arguments that are given, are probable reasons to double check everything before startup.
But at least you have a workaround for most of the issues.
I think that if you define the K-factor for the filament you use, it might skip the flow dynamics calibration.
But that is something you can easily check.
Yeah, sure, but that (and also what Gerrit wrote) will also apply to RFID filament but with RFID filament everything works as described.
I mean I can always try and force cheating the system but then I have options “Auto”, “On”, “Off”.
And “Auto” only works for me only for RFID filament as described where I can’t see a reason why this should behave differently as this can be “cheated” the same way.
Anyway, it’s no big deal and disabling unloading/flushing via the described wiki entry already helps.
From what I understand this will retract a bit of the filament, then cut, then unload.
What I don’t understand is the warning regarding nozzle clogs or other print problems. Why should that be an issue?
On my Prusa (with MMU3) it onloads it completely, no cutting at all. And in more than a year of using it I had zero nozzle clogs. Why should it cause clogs with a Bambu?
Has anyone of you used the “long retraction when cut” feature already?
For me that sounds absolutely reasonable to leave as little filament as possible in the nozzle/hotend and again, that’s what Prusa always does and it works with zero issues.
