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donmilne

Cura behaviour change? - just curious

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Cura 14.6.1 + IRobertl's bugfix firmware + UM2

Over the last couple of days I've done two print jobs whereby I printed off two copies of an item at the same time (one gcode file).

I was surprised to see my UM2 print one copy completely, before raising the bed again and printing the other copy.

In the past it has printed layer N for all copies before moving to layer N+1, so all copies finished at the same time.

Can someone confirm this new behaviour? And if so I'm curious as to what advantage it brings (except perhaps that can abort the print and waste less material when I see some problem in the object? Ditto if the material sticks or runs out).

 

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In Cura there are 2 modes of printing in the Tools menu.

Try loading the profile from the gcode in cura (File->Load Profile from gcode) and look at the Tools menu to see if its set to "print all at once" or "print one at the time".

The advantage depend on the model you print. You might get better results if the head is not constantly going from one model to the other at every layer. Or you might want to use the "Spiralize the outer contour" option from the export settings while printing more than one model.

 

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I've never consciously set any such feature, so if the behaviour changed then the default must now be different. I believe I do prefer the one-at-a-time approach. In the past I've printed (say) six copies at once, and if the filament jams halfway through then all six copies have to be junked.

On the other hand, the things I've been printing recently are quite short. If they were tall and printed one at a time, I guess there would be a danger of the printhead running into a previous copy. Perhaps Cura has a test for this, and that's why the behaviour change.

 

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if you print one at the time Cura will include the print head size into the needed space between each models. This is the dark rectangle you see on the bed when you select a model. Printing one at the time will reduce your potential print space due to the print head clearence it require.

Also depending on your model you may want to print all at once to give time to your other models to cool.

 

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There are settings in machine settings that set the size of the print head around the nozzle and also the gantry height. If even one object violates the gantry height or if it can't print all the objects with the size limitations then cura automatically does "all at once". That's why you probably didn't see this before - either they were taller than gantry height or you put them too close together.

For me the nice thing about one at a time is if things fail part way through at least you have potentially the first print being fine. Also I have had problems in between prints that sometimes when it primes the nozzle before the second print it makes a mess that can get caught on the head and mess up the second part.

Also all-at-once might get you tons of stringing if you don't have your retraction settings dialed in.

Also if you did a sloppy leveling job then you might print the first one fine but when it moves to another part of your print bed the bottom layer might not be so good.

Also all-at-once is much slower as it has to retract and move back and forth between all the prints on each layer.

 

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Also all-at-once is much slower as it has to retract and move back and forth between all the prints on each layer.

 

One at a time can be slower if you have small prints, due to minimal layer time.

Note that this feature is not new, it's been possible from version... 12.08 I think. But it came more accessible in 13.06. It's one of the features I personally really like, and I think Cura is the only software that does this right now.

There are a whole bunch of constrains for one-at-a-time, as explained above already.

 

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I ran into a problem with this feature yesterday. I was printing off IRobertL's replacement UM2 feeder, all parts at the same time. The UM2 printed each component separately as described above. However at one point I saw my whole print bed flexing, quite alarming! On closer inspection the y-axis bar was scraping the top of the feeder_v4_arm object while it printed the v4_feeder_body part that came after it. It's a testament to how well "brim+PVA" works that the tall component wasn't getting knocked over.

I assume there's a setting somewhere to increase this clearance, but you might want to take a look at the defaults. My other suggestion is to print the shorter components first.

 

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