Thanx for the insights!
On 1/5/2023 at 6:37 PM, GregValiant said:Within the project file you have the Extruder #1 "Nozzle Switch Extra Prime Amount" set to 40mm³.
Fixed that, but was still having tool-change blobs (and was previously blobbing on all extruder changes, not just when engaging that one).
Played around with the various retraction settings, and it seems the culprit was the relatively large *difference* between the 'regular' and the 'tool change' retractions.
With the 6mm (regular) retraction and default 16mm 'nozzle switch retraction', you showed how Cura was first doing the E-16, Tx (tool change) then E+10 (=16-6, pre-priming?) of the new color. It's that E+10 on the new tool/color/extruder that causes the blob before moving to the prime tower, where it un-retracts 6mm before printing/priming on the tower. I set the 'nozzle switch retraction' to 6mm (matching the 'regular' retraction distance), and the blobs disappeared. This means I need more priming after the tool change to clear out the previous color, but increasing prime tower volume seems to help compensate, as well as printing walls from inside out to hide the still-transitioning color...
It's a mystery to me why Cura does the new tool un-retraction/pre-priming BEFORE moving over to the prime tower, but there it is. (probably just easier to program that way for the case where no prime tower is in use...)
Thanx again for the pointers! I think i can at least try a real multi-color print now with some hope of success...
PS, I think I grok the math of how it's trying to maintain the working nozzle pressure by pre-priming the new extruder by as much as it does, but perhaps the idle extruder sitting at temp leads to a very molten first squirt of the new extruder? ie, why else would not even equalizing the previous pressure cause a blob? (as you pointed out E-16, E+10 should leave the filament 6mm behind the tip, but it doesn't, for some reason) I may play around with a NEGATIVE value for "Nozzle Switch Extra Prime Amount" (instead of a giant positive one!) to see if that helps...
Edited by pozzello
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GregValiant 1,342
Within the project file you have the Extruder #1 "Nozzle Switch Extra Prime Amount" set to 40mm³. That's 16.63mm of filament on top of the 16mm regular prime amount. That will leave a mark.
Your "Dual Extrusion" settings for Extruders 2 and 3 look reasonable and neither have any extra prime (much less 500mm worth of extrusion in a blob). You need to set Extruder #1 up the same as 2 and 3.
There is no G1 F2400 E-16 because you set Cura up for Absolute Extrusion rather than Relative extrusion.
This is what is happening every time Extruder #1 gets over the print and starts its first extrusion:
G1 F1800 X120.359 Y116.04 E203.41115 --- Last extrusion of the previous tool and the filament is right at the nozzle
.....
G1 F1200 E187.41115 --- Nozzle switch retraction of 16mm for the previous tool
.....
G92 E0 --- Reset previous extruder to 0
T0 --- Switch to Extruder 1
G92 E0 --- Reset Extruder 1 to 0
G1 F2400 E10 --- 10 mm prime (16 minus your regular retraction distance of 6.0) The filament is 6mm behind the nozzle.
....
G1 F2400 E32.63007 --- Here is the problem. For the other extruders this is E16.0 but for Extruder 1 it's adding that extra prime of 16.63mm (40mm³) that you have asked for in your settings.
PS: I just had another look at the project file I posted in the alternate thread and it's fine. That "40mm³" of extra prime came from somewhere else.
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