Nozzle ooze during calibration

Is there are reason the bed and nozzles must be heated during calibration? Even after unloading the filaments the nozzles often oozes after heating which then screws with the calibration, often requiring many re-tries.

Printer parts involved in printing process directly are heated up to some extent - hotends more, printbed - less. Still most of any material printers are made of will change their dimensions with temperature. If you would run calibration at room temperature, you will arrive to one setup, likely different from the one you should have at real printing temperatures. Even if we speak about hundreds of a millimeter, for the first layer adhesion or alignment of both printheads this will be crucial.
If remains of removed filament are still oozing you can try to load some with a bit higher melting temperature like PET-G or ABS, remove it and run calibration as regular. Oozing shall not be present any more (as to my experience) but you shall remember you have remains of more heat resistant filament in hotend if lover temperature filament like PLA is loaded for job - either choose higher temperature for loading (if PLA still can push foreign filament remains through) or do it in steps like ABS–>PETG–>PLA.

Another option would be to wait until oozing has stopped. This is how I do it when I recalibrate the printer and don’t want to change the filament.

With my PLA (non-Snapmaker) and my hotend being upgraded according to the “original clogging solution”, this takes about 5…10 minutes.

Here is my solution to the oozing…

  1. Remove the Bowden tube,
  2. Open the filament feeder door on the side of the hotend
  3. Once the hotend is up to temp, pull out the filament.
  4. Take a stiff wire a bit smaller in diameter than your filament and ram it down the hotend to push out any remaining filament.
  5. Proceed with calibration

This process forces all of the filament out, except for the tiniest amount right in the 0.4mm section of your nozzle. I am using a piece of stainless steel spring wire that is 1.60mm in diameter (1/16" for those in the US) that I had sitting around from an old project. If you wander the aisles of your local hardware store, you should be able to find something suitable.