It's not possible to print multi extrusion in one at a time mode at the moment.
Ah.
It would be much better if this was still possible as All at Once is messier and I need the automation to print more than one part.
I guess the issue is you'd need an extra wipe tower printed per part?
I have Print Sequence checked in settings but it doesn't appear under Special Modes on the right.
Ok, so if my UMO is set up as dual extrusion, it is not possible to select "one at a time" as it always is related to the dual setup in my json...
Is there a way to select something like a "non" material on the second extruder or is the only workaround to add an additional printer with only one extruder...?
How is it possible to select the second extruder as e.g. it is loaded with a different colored material to perform a "one at a time" print with it before unloading the first extruder...? (often do this as my first extruder is always loaded with black PLA)
I know, many questions, but maybe @nallath could give a hint?
Ok, so if my UMO is set up as dual extrusion, it is not possible to select "one at a time" as it always is related to the dual setup in my json...
Correct
Is there a way to select something like a "non" material on the second extruder or is the only workaround to add an additional printer with only one extruder...?
Not at the moment. We are planning to enable the possibility for one at a time dual at some point, but it proved to be a tricky issue to tackle and had to make tough choices at some point. One at a time dual was one of the victims.
A work around is to change the machine definition files (If only one extruder is used, it should work perfectly, but the setting visibility has no notion of what extruders are actually used at the moment)
I guess it also makes sense right. The required pathing for the head switching could hit previously printed objects, or wiping towers etc.
Ok, so if my UMO is set up as dual extrusion, it is not possible to select "one at a time" as it always is related to the dual setup in my json...
Correct
Is there a way to select something like a "non" material on the second extruder or is the only workaround to add an additional printer with only one extruder...?
Not at the moment. We are planning to enable the possibility for one at a time dual at some point, but it proved to be a tricky issue to tackle and had to make tough choices at some point. One at a time dual was one of the victims.
A work around is to change the machine definition files (If only one extruder is used, it should work perfectly, but the setting visibility has no notion of what extruders are actually used at the moment)
Thanks for clarification! so I will add an additional printer...
b.t.w. what about reactivating the "change extruder" post processing plugin ?
Change extruder post processing plugin? Could you refresh my memory a bit?
Sure :-)
Made by Dim3nsioneer, working perfectly to select the extruder which you'd like to print with.
More infos here:
https://github.com/Dim3nsioneer/Cura-Plugins/wiki/Select-Extruder-plugin
Would be great to have it working also for the new Cura...
Sure :-)
Made by Dim3nsioneer, working perfectly to select the extruder which you'd like to print with.
More infos here:
https://github.com/Dim3nsioneer/Cura-Plugins/wiki/Select-Extruder-plugin
Would be great to have it working also for the new Cura...
As long as Cura 2.x doesn't have a g-code importer yet, there isn't really a point to this.
Edited by GuestThanks, got it :-)
(UM2Go) using one at a time, when the second object starts, it looks like there is no material in de nozzle, due to a retraction before switching objects?
The second object fails because the first layer gets no material. Can someone confirm this?
This has happened to me also. I usually add extra skirt to fix this. or brim.
can this be solved in the gcode? @nallath?
I know this now, will probably forget it a couple of times, and it will result in a lot of number 1 items and too little number 2 because you have to start over again..
And everybody else who does not realize this will have the same problem.
You want to start every print well primed and using an overkill of skirt seems stupid to me..
Hi @nallath, I have just tried this with single extruder printer and it is not right. The model is 17.5mm*15mm*2.5mm. I loaded the model and created 3 copies. I then moved them apart giving 70mm between each copy.
I turned on print one at a time and two things happened
1. each of the 4 models has a very large grey area, circa around 120mm*80mm. Due to their size there is some overlapping. I have 1 line of skirt 3mm from the model.
Does the overlap mean they will not print?
2. I get the message that the build volume height has been reduced to prevent a piece being hit by the gantry. The pieces are 2.5mm high and the Printer settings have the gantry height set to 70mm!!!!!
can this be solved in the gcode? @nallath?
I know this now, will probably forget it a couple of times, and it will result in a lot of number 1 items and too little number 2 because you have to start over again..
And everybody else who does not realize this will have the same problem.
You want to start every print well primed and using an overkill of skirt seems stupid to me..
It should be possible to fix this in the g-code, but it would be better to fix this in the generation. Up until this point we weren't aware of the issue.
1. each of the 4 models has a very large grey area, circa around 120mm*80mm. Due to their size there is some overlapping. I have 1 line of skirt 3mm from the model.
Does the overlap mean they will not print?
Once at a time is... tricky. It will now draw 2 disalowed areas for each object. This has to do with the size of the head and area's it can no longer print due to another object being there. There is no real easy way to explain this, just try and play around with it a bit.
2. I get the message that the build volume height has been reduced to prevent a piece being hit by the gantry. The pieces are 2.5mm high and the Printer settings have the gantry height set to 70mm!!!!!
Yes, this makes sense right? A one a time object can be bigger than the gantry height. If that would be the case, the gantry would hit the first object when printing the second one. There is a damn good reason why one at a time is not the default 
G1 F1800 X119.437 Y107.840 E391.44929G0 F9000 X118.800 Y108.701M107G92 E0G10G0 X118.800 Y108.701 Z14.999G0 X110.001 Y132.914;Layer count: 49;LAYER:0G0 X104.001 Y126.914 Z0.300;TYPE:SKIRTG11G1 F1200 X126.000 Y126.914 E5.27976
Above is the code generated from cura 15.04.4 (what version are you using @peggyb ?)
If there is a bug it's probably related to the G92 E0. The G10 does a retraction and the G11 undoes that. But I'm thinking the G92 E0 which resets where the firmware thinks the E axis is positioned back to zero and this somehow makes the G10 retract too much or insetad makes the G11 do nothing. I guess G11 doing nothing is more likely.
Either way it seems more like a Marlin bug and not a Cura bug. Maybe this was fixed? Did you try latest firmware @peggyb? Or was this on a UMO? I think you said um2go. Sorry didn't reread.
1. each of the 4 models has a very large grey area, circa around 120mm*80mm. Due to their size there is some overlapping. I have 1 line of skirt 3mm from the model.
Does the overlap mean they will not print?
Once at a time is... tricky. It will now draw 2 disalowed areas for each object. This has to do with the size of the head and area's it can no longer print due to another object being there. There is no real easy way to explain this, just try and play around with it a bit.
2. I get the message that the build volume height has been reduced to prevent a piece being hit by the gantry. The pieces are 2.5mm high and the Printer settings have the gantry height set to 70mm!!!!!
Yes, this makes sense right? A one a time object can be bigger than the gantry height. If that would be the case, the gantry would hit the first object when printing the second one. There is a damn good reason why one at a time is not the default
Hi @nallath, OK let us take no.2 first. No it does not make sense to reduce the height of my model when the gantry is 67.5mm above the highest point of my model!!!
No.1, maybe a bit more complicated. With a particular set of parts, all 2-3mm high, I always print 4 or 6 copies together. For the past three years with 13/14/15.nn I have nearly always used one at a time - for me it is the much better option. If the print fails say 60% of the way through, instead of having 4 unfinished models I will have two finished models. Also it can be cleaner with no trails between the parts - although these days with more experience I have retraction right and do not usually suffer from this.
15.4 backwards had a much smaller disallowed area and I could easily fit 6 on the bed and probably 9 although I never tried that. I am expecting an order for 500 of the parts which I had planned to print at at least 6 up- if I can only fit 2 or 3 on the bed I will need to go back to 15.04 which will be a shame because I am getting a better top layer finish with 2.3, the top surface is quite complex causing quite a lot of retraction during the infill.
I guess my point is that with 15.4 etc. everything was fine so I can only think that 2.3 is doing this wrong - it is the same part and the same printer.
@yellowshark, I am using 'one at a time' a lot also. And I think it works almost the same now as 15.4, except still missing the multiple copies.
Did you try overlapping the 'fan shadows'? You can overlap the shadow of object 1 to the thin skirt shadow of object 2.
The gantry warning is correct, you will notice that your build volume is lower now, but it would make more sense if it showed up with object higher then the gantry, because lower objects aren't the problem.
@gr5, I am using 2.3.1 (as in the title) with my Um2Go, and suspected it has something to do with the retraction gcode, and was hoping somebody else could check if the gcode generation is to blame (or the user..) @yellowshark, does this happen to you as well?
Hi @nallath, OK let us take no.2 first. No it does not make sense to reduce the height of my model when the gantry is 67.5mm above the highest point of my model!!!
We don't change the model, we change the height of what the printer says it can print.
No.1, maybe a bit more complicated. With a particular set of parts, all 2-3mm high, I always print 4 or 6 copies together. For the past three years with 13/14/15.nn I have nearly always used one at a time - for me it is the much better option. If the print fails say 60% of the way through, instead of having 4 unfinished models I will have two finished models. Also it can be cleaner with no trails between the parts - although these days with more experience I have retraction right and do not usually suffer from this.
I fully understand why people want one at a time. I'm just saying that it's a pretty difficult way of printing and introduces quite a few additional constraints.
PeggyB is correct as for the shadows; The outer shadows can overlap outer shadows of other parts, but outer shadows may not intersect with inter shadows of other parts.
The Old Cura had a pretty naive way of setting the size of the head; You could only set a width & height (aka; bounding square). Cura 2.x can use a polygon, which should allow you to pack more objects on the plate in quite a few cases when printing one at a time.
Hi @nallath and @peggyb, thank you both for your help, it is all clear now and I should have read the message more carefully and prevented my misunderstanding! I can get at least 6 on the bed so I am happy now 
I have always thought that if the user could select the sequence of printing and, say you were printing a row left to right, then if Cura could navigate itself back to the left hand side, the right hand side fan shadow could be removed and more units could be loaded on the bed.
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nallath 1,124
It's not possible to print multi extrusion in one at a time mode at the moment.
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