need help fine tuning multiple object print

[peetersm 124]

Any advice is greatly appreciated. I am having trouble going from single object print to multiple.

I work at a small elementary school which focus on “STEM curriculum”, we have several 3D printers (FYI - the ultimaker1 is my favorite). I often need to print ~120 of the same object or similar objects (if the kids designed their own). So I find myself wanting to find a good balance between producing good looking prints with high production volume.

My current need is to print a bunch of tree ornaments. I can change anything about the model in order to make it print faster and better, and I think I have created the best model I can by following the process detailed below. What I am having trouble with now is to figure out... Why I am getting so much blobbing on these prints??

This tree prints pretty good one at a time, but when I print a bunch at once I get a lot of blobs, more blobs than I would anticipate due to stringing. This pic compares a tree printed in a group with a tree printed alone.(same print-slice settings used on both)

more prints showing my progress in this album

 

FYI - My thought process for making a model that will print fast and pretty, and how to print a lot of them:

1. retraction should be avoided (because is slows down the printing and can make yucky blobs) – so try to make as much of the model as possible so that it will be sliced as a single path outline, or each layer is a solid path with no retractions needed. So I make the smallest dimension equal to 2 x Nozzle size, and for parts larger that 2xnozzle keep them small enough to not become too week when sliced with the following settings.

To minimize retraction slice with:

Shell thickness=nozzle size

Fill Density=zero

Printing speed = as fast as you can (for me this is usually 70mm to 100mm)

2. Go for long print runs. Removing objects, replacing tape, and re-starting a print jobs takes time..and usually if the 1^st and 2^nd layers print well you leave the machine alone and just check on it every hour. Make a STL file with a bunch of copies on the bed, since letting CURA do this puts too much space between them, you need to make your own full plate with the objects closer. Also this will make CURA print all objects at once (the ability to manually set this in CURA comes and goes from release to release).

 

[nick-foley 5]

Without seeing values you used to print, it's hard to get too specific, but here's the "blob reduction checklist":

- Increase Retraction Speed or Distance

- Increase Travel Speed

- Decrease Temperature

- Upgrade to the latest beta version of Cura which handles retraction movements better.

 

[illuminarti 18]

The blobbing is happening on the jumps from one piece to another. From the stringing in some of those pictures, it looks like retraction is totally turned off. That's going to make a mess. If you're printing multiple objects at once, you need to have retraction enabled, or else you'll get strings and blobs.

Also, in expert settings, I would suggest trying to turn off 'enable combing', as that can sometimes cause too little retraction to happen as well.

I would recommend building an up-to-date version of the firmware, and using that, as that fixes a problem that makes retraction speeds unreliable. The fix is still not in the official version of the firmware that comes with Cura, even though the fix 9 months old now.

Also, as Nick suggested, make sure the travel speed is quite high. You can probably go to at least 250mm/s on a well-set up printer.

The beta version of Cura he mentioned is at:

http://software.ultimaker.com/Cura_closed_beta/

 

[tommyph1208 55]

So, just to clarify... You are printing a bunch (from the size details provided in the picture I'm guessing 9?) of trees in a single print run...?

How does these print? One layer at a time for all models or finishing an entire model before moving on to the next?

If its the first, possibly the blobs could have to do with the start and end of travels between models, finishing an entire model before moving on to the next should effectively mimmick the print quality you get from printing just a single model in a run...

 

[nick-foley 5]

Actually, maybe my suggestion of switching to Cura 13.12 for better retraction was wrong; having some problems with that at the moment.

 

[gr5 2,234]

One layer at a time for all models or finishing an entire model before moving on to the next?

 

If you had read the whole thing or even skimmed it you would realize that this teacher doesn't want to print one-at-a-time because this teacher understands that prints can fail often but usually they fail on the first layer or 2 and yes of course the blobs are related to travels between models also known as stringing.

 

[gr5 2,234]

In cura expert retraction settings it is very important to set both minimum distances to zero. If you don't do this Cura will not retract very often at all.

Printing one tree at a time is much faster if you are hanging around the printer. All those retractions slow things down. But if you want to leave the printer alone for 2 hours I understand how you might want to print 12 at a time.

I would be tempted to just let it print during class and after each print walk over for a few seconds, pull off a print and start the next. By the time you get to print #4 you will be able to do it without interrupting a lesson. It might help to have a clipboard saying the name of the next print to do from the SD card.

 

[nick-foley 5]

I get much higher quality prints when printing all objects at the same time, and group prints whenever possible, particularly when things are small. From a cooling/curling/deforming from heat perspective, printing two of the same object at once is equivalent to cutting your extrusion temperature in half!

Also, there's something awesome about setting up a print, letting it go overnight, and waking up to a machine packed full of beautiful stuff.

 

[peetersm 124]

thanks all for the great input, here's my retraction setting details and what I am going to try next (following suggestions):

was using will try (new settings)

retraction speed=40.0 retraction speed=40.0 (this is default do I need the make it higher too?)

retraction distance=4.5 retraction distance=4.5 (default again, not sure if this is high enough?)

Travel Speed=70 Travel Speed=150

retractions min travel=1.5 retractions min travel=0

enable combing=yes enable combing=no

min ext before retract=0.1 min ext before retract=0

I will also read up on the firmware build..if I am understanding , do i just download the beta 13.12 CURA and let it update the firmware on the arduino board of the ultimaker1 when it asks? then mabye switch back to using the stable version(13.11.2) for slicing and printer control?

I should have some more pictures tonight. :-) thanks again!

 

[illuminarti 18]

You retraction speed and distance should be ok. Although due to the bug, you'll probably only get half the speed you ask for. To update the firmware you need to either get the source code and compile it, or use:

http://marlinbuilder.robotfuzz.com

The version of Marlin for the original Ultimaker that is included in all versions of Cura hasn't changed since last March. The changes in the most recent versions of Cura relate to how and when retraction is requested, not how the firmware actually makes it happen.

The new settings should work better... you might find you get too many retractions with the minimum travel distance set to zero; if so, you could safely increase that to 1mm, I think.

 

[gr5 2,234]

if so, you could safely increase that to 1mm, I think.

That's fine but don't increase the "min ext before retract" above 0.

I have a "robotfuzz" version of Marlin but the improvements are unlikely to help you much. The defaults will increase the retraction speed from 20 (even though you asked for 40) to 25. A small increase. Leave it at 40mm/sec in Cura - if you try 45 you will I believe get even *less* speed. Illuminarti has a large experiment/article about this here:

http://umforum.ultimaker.com/index.php?/topic/1734-marlin-bug-the-myth-of-retraction-speed/

 

[gr5 2,234]

By the way - watch the filament in the clear bowden tube when retraction occurs. Look at the top of the arch. The filament should go from the top of the tube to just barely resting on the bottom of the tube. If not, increase retraction distance a little bit - maybe from 4.5mm to 5mm. Mine is set to 4.5 and works great.

 

[peetersm 124]

That's fine but don't increase the "min ext before retract" above 0.

What should the path look like? I am trying to make sense of the tiny blue lines going up that indicat retractions. See the picture. should I strive for a single retration line when the path leaves the circle part of this layer (kinda like the far right settings) or should I expect two lines one when it begins the circle area and one when it leaves?

 

[peetersm 124]

Also, in expert settings, I would suggest trying to turn off 'enable combing', as that can sometimes cause too little retraction to happen as well.

Just by looking at the path I can tell turning off combing should help a lot. see the picture of the path changes and the picture of the blobing I expect was caused by the "off object" retracting.

 

[illuminarti 18]

The min extrusion before retraction setting is just to stop it retracting repeatedly on the same spot of filament. For something like these prints it's not really an issue. It cancels a retraction that would otherwise of have happened if you haven't moved the filament forward some minimum amount since the last retraction happened. You can set that to zero.

The min travel setting specifies how far to you have to move to get a retraction. The print head will often do lots of little moves within an island as it goes from inner loops to perimeters, and then to any infill that is needed. You don't normally need retraction for those, since they are tiny moves, and internal to the print body. But when making longer internal moves, or when moving between islands, then you want to retract. Hence, set the minimum travel setting to a small number of mm, to allow the smallest of internal moves to happen without retraction, but anything longer to use it.

The aim is to have a retraction happen immediately before leaving as island, but not within the island, unless it's a very large island, with long internal moves.

What should the path look like? I am trying to make sense of the tiny blue lines going up that indicat retractions. See the picture. should I strive for a single retration line when the path leaves the circle part of this layer (kinda like the far right settings) or should I expect two lines one when it begins the circle area and one when it leaves?

[peetersm 124]

I guess I thought (incorrectly) that Cura generates a retract only when moving the head over "empty space" or from one island to another. Now I think it's making retractions when ever it's not actively printing, so even moves inside the object (like the solid layer in the picture) will retract if it's turning a corner, or positioning the head for another pass of solid fill. ?yes?

 

[illuminarti 18]

if you enable combing, then Cura prefers moves within an island when it can, and all moves within an island have no retraction. But that causes other issues currently, as you saw.

Failing that, Cura retracts whenever it makes a non printing move, such as between lines of infill, or areas within a shape, or between shapes - if the distance being moved is greater than the minimum travel amount, and the amount of filament used up since the last retraction is greater than the minimum extrusion amount (measured in terms of mm of filament fed in).

So in your test case above, with a minimum travel of 0.3mm, it retracts on every move between infill, since the lines are spaced 0.4mm apart. if you increase that to say 1.5 or 2mm, then it's only going to fire on moves between areas or islands, rather than just between adjacent lines.

Provided the minimum travel setting is greater than the smallest distance between your printed objects, at their closest, then you'll always get retractions when moving between objects.

 

[gr5 2,234]

In post #13 above you have a triple picture showing slice view and expert settings. Clearly the first and last are ideal (for this layer anyway) as you don't get more retractions than necessary. However you did it by messing with "min extrusion..." instead of "min travel...". It's much easier in my opinion to mess with the second (min travel). It is clear - it says if the movement is smaller than this, don't retract, if the movement is larger, do.

The other one, "min extrusion..." is more complicated. With .2mm layer heights use a multiplying factor of 100X meaning .1mm here means 10mm of printing lines. If you print less than 10mm of printed path it will not retract even if going to another island. This is bad. 10mm might not be enough. Plus you can get out of sync and it might do retracts only *within* islands on the next layer. So I strongly recommend you keep "min extrusion..." to 0. Always zero. This is a recent feature (only a few months old) and I think it's a bad idea. It's intended to keep you from grinding the filament but instead seems to result in ugly prints.

The other one, "min travel..." -- feel free to mess with that. Like Illuminarti says, try to give it a value that is always smaller than the distance between two "islands". I usually just give it a value of 0 or 1mm and enable combing but combing can cause other issues. For these trees it sounds like a value around 1 to 4mm might be a good value for you.

edit: bold word above was edited (fixed).

 

[Daid 306]

I have noticed this myself, I think I managed to put a fix in the 13.12-test from http://software.ultimaker.com/Cura_closed_beta/

Cura is trying to move the head inside the print area before retracting (so it retracts inside the print instead of on the edge), however, on small things this means the head moves actually outside the object instead of inside. I've put an extra check in place to make sure the final position is inside the print, else it does not do this extra move before retracting.

 

[peetersm 124]

I really appreciate the expert help and your patience guiding me through this! I have posted pics of my latest prints, looking much better.

I delivered the trees to the 1st, 2nd and 5th grade classrooms today and they were very pleased. They were all waiting on the trees since last week they worked in pairs with openSCAD to make thier own tree modifications and posted pictures of thier individual trees to our classroom forum. I was able to tell them about how much I learned in the past few days and how grateful I was for the chance to deepen my understanding of the slicing and printing process. A wonderful example of the problem solving process, I showed them slides of the yuckiest prints and how (with your help) the prints got better, I was able to tell them all about how I was stumped by this printing job, and how i was able to find help from the amazing open-source community here. (I even included a slide of this forum in my presentation and some of the slice/head path photos from CURA)

anyway, please know how much your time and willingness to share your knowledge is valued.

 

[gr5 2,234]

So you have a makerbot also? Were the red trees on the makerbot and the green trees on the ultimaker? Both look incredibly similar in quality - for example both have trouble with the ring on top.

 

[illuminarti 18]

Excellent!! I'm glad you were able to get better results for your students, and for your own peace of mind!!

[peetersm 124]

gr5 - I do not have a makerbot (I try to only expose the kids to open products) the red was printed on the MakerGear M2 and green on the Ultimaker1 (we also have a TypeA Machine Series 1 but it needs a new bed so it was not avalible at the moment) and both did have trouble with the top ring. Even after lowering the temp a bit and slowing things down the top ring was fussy. If I tried to print it filled it would be blobby, if I tried to print it hollow it was weak. I told them if the top breaks off maybe use to for a table top decoration, or use that as a chance to design a new hanging mechanism . :-)

[gr5 2,234]

Regarding those rings: It's tough to go from zero extrusion (retraction even) to 70mm/sec printing instantly. It takes a 100millseconds or more to get up to speed. So for larger things like the tree itself you don't notice as much the bad spot before quality improves. For the tiny ring it's obvious. The simple solution would have been to slow down the printer to 40% feedrate when you got near the top of the tree.

The quality of the trees would have been improved greatly at 30mm/sec but it also would have taken more than twice as long so it's a tradeoff.