Cura Questions

I want to start a new thread here, but this is partly associated with my post earlier about jams which seem to be related to retraction issues.

In an effort to try some things differently, I sliced a few of my designs with Cura and printed them this afternoon. One of them did great, although I noticed that even though I had set the support settings, it did not create on support where I thought it should. I believe that Slicer has a max bridge setting, but I am not finding that in Cura. Am I just missing it somewhere?

Cura has a setting, like Slicer, to widen the first layer. Except that in Cura, it does not work as I expected and as it seemed to in Slicer. In Slicer, the extruder seemed to actually extrude a little extra filament and made the lines wider. In Cura, setting the Initial Layer Line Width to a larger percentage just makes the same width lines, but farther apart. Setting it back closer to 100% and the lines are tighter.

In Cura, I set the retraction to on and 1.5mm. I set the minimum extrusion before retracting to 1.5mm. I enabled combing. It does not appear to me that any retraction is occurring at all. The up side to this, is that, so far, my filament jam problem has not reappeared.

Any advice appreciated.

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Originally Posted by CalifDan

In an effort to try some things differently, I sliced a few of my designs with Cura and printed them this afternoon. (1) One of them did great, although I noticed that even though I had set the support settings, it did not create on support where I thought it should. (2) I believe that Slicer has a max bridge setting, but I am not finding that in Cura. Am I just missing it somewhere?

(3) Cura has a setting, like Slicer, to widen the first layer. Except that in Cura, it does not work as I expected and as it seemed to in Slicer. In Slicer, the extruder seemed to actually extrude a little extra filament and made the lines wider. In Cura, setting the Initial Layer Line Width to a larger percentage just makes the same width lines, but farther apart. Setting it back closer to 100% and the lines are tighter.

(4) In Cura, I set the retraction to on and 1.5mm. I set the minimum extrusion before retracting to 1.5mm. I enabled combing. It does not appear to me that any retraction is occurring at all. The up side to this, is that, so far, my filament jam problem has not reappeared

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If you haven't seen it, user dacb started a thread for discussing and optimizing Cura settings - http://3dprintboard.com/showthread.p...-Cura-settings

(1) You'd have to elaborate on the support issue. I haven't had problems, but the only print where I've used support has been on the extruder base.

(2) Cura doesn't have any settings specific to bridging, and it does get flack for that. Before I switched to Cura, I read through a number of the Cura threads on the Ultimaker support forum. The main developer behind Cura is philosophically against giving the user the option to frequently change things like print speeds for bridging. His argument is that the extruder can't make instantaneous changes and that the flexibility will get many people into print-quality trouble if they don't understand the limitations in what they're asking for.

(3) I observed the same thing with the first layer width setting. I'm currently using Cura Engine embedded in Repetier-Host, so I don't even get that setting. When I transitioned from Slic3r to Cura, I found the first layer to be troublesome. So have others. Admittedly I can't get as good of a first layer in Cura as I could in Slic3r, but I also no longer heat the build plate for PLA so I don't know how much blame to put on Cura. Here again we're dealing with the philosophical attitude behind Cura. I remember the developer stating that wanting to over-extrude on the first layer was outright stupid. I also remember reading when the developer caved to overwhelming pressure, showing a GUI picture where the width option was added, with a comment that users would have to provide their own script to do anything with it. I stopped following Cura threads, so I don't know if that is still the case or if functionality was added before the setting showed up in a released version.

(4) Can't speak to combing. Your changes in retraction settings are intended to reduce the number of times retraction occurs. That's the whole point. Depending on the print, retractions may not occur. If the settings seem too conservative, back down on the minimum extrusion before retraction. FWIW, I no longer assume the same retraction settings will apply to all prints. I look at the complexity of each print, and like print speed and temperature, somewhat tailor retraction to suite. For simpler prints without a lot of perimeter crossing, I disable it. Due to what appears to be smarter track algorithms in Cura, I have found I can print without retraction in Cura more often than I could with Slic3r.

Printbus,

That was helpful, thanks. I was curious about your comment that you do not heat the bed for PLA? Could you elaborate your reasons and results of doing so? I don't heat it a lot (about 70-75 C, but I wonder how you make it stick without heat?

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Originally Posted by CalifDan

That was helpful, thanks. I was curious about your comment that you do not heat the bed for PLA? Could you elaborate your reasons and results of doing so? I don't heat it a lot (about 70-75 C, but I wonder how you make it stick without heat?

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In a round-about way, Cura drove me to it. In my first attempts with Cura, I couldn't get my first layers to stick to the hair-spray coated glass I had been using. I started working through options others have used, and bumped into the near permanent bond that forms between PLA and 3M blue painters tape swabbed with alcohol. Here the challenge is often figuring out how to get the print off the bed, and printing on a heated bed just makes it worse. Others here are reporting good success with things like Elmer's glue stick instead of painters tape. You just have to research and experiment.

Regardless, I concluded there's no way Cura extrudes the same amount of material on the first layer. I found it best to run with slightly less gap between the glass and the extruder tip, and I now adjust that with the nozzle hot. If I had started with those changes, Cura might have done fine with the heated hair-spray bed. I don't know.

I dont think I have ever messed with the first layer settings in Cura, I think its set to a 0.3mm height?

My main thing was adjusting my Z stop (first layer position/gap to the bed) when the bed and the head were hot.
I preheat my bed and head for at least 8 minutes before I start a print. Then I let it print the skirt, if it looks good, I let it continue, if not, I stop it and adjust my Z stop accordingly.
I print my first layer pretty low, it smashes that first layer down pretty good, this has worked well with ABS 90C on hairspray, and PLA 70C on just glass.
Once the printer has been running most the day, I can just do one print after another, but the first one or two prints usually need adjustment, even with the preheating.
(I really need to take the time to setup the auto leveling)

As far as how much Cura extrudes on the first layer,
If you want, you can use the Tweak at Z Height plugin, this lets you tweak settings at certain heights.
So you could tell it to use a higher flow than 100% at the first layer, then set it back to 100% for the rest of the print.