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Noob Questions about Different Slicing Techniques

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Hello Ultimakers!

My name is Luc, a brand new user, both to the Ultimaker and these forums. Recently, I've been reading a lot of forum posts in which people are talking about different slicing engines for varying applications. Apparently, some are better than others at certain things, and as a clueless noob, I was hoping to create a post in which a large amount of this kind of information can be compiled. I haven't seen a post like this yet; I've just been catching hints and glimpses at what people are talking about individually. Usually though, I have no idea what they are talking about.

So Ultimakers, can you explain different slicing engines to me like I'm 5?

I have taken an interest in this topic recently when I noticed a part that I was printing started taking VERY strange paths to complete the print. Basically, the part was finishing up and had only a few tall spots to complete, so it was jumping all over the place to finish these last few posts. However, the order in which it was trying to complete this part seemed chaotic. In fact, sometimes, the part would move from one post to another, and not even try to retract. I was left with long, full beads of material strung between opposite sides of the part. Pics 2 and 3 in this album really highlight this problem.

http://imgur.com/a/YSKay#DLzVzPH

Now, these were fairly easy to clean, but I can't help but wonder what the heck was going on with the gcode. I have a 7 second layer timing built into the programming. Is it possible that the gcode is trying to stay within this parameter by jumping all over the place, seemingly out of order of what the most efficient print would be?

Additionally, the 4th picture in this album shows another problem with the 7 second layer timing parameter. Once the part was trying to finish up the very last layer of the top of the flange, it slowed down to a snails crawl, in order to keep the "7 second rule," and basically way over extruded. Does anyone else out there play around with this layer timing? What can be done to prevent this last second globbing caused by over extrusion?

Thanks for reading. I know this was a lot at once, but you guys have been so awesome so far.

 

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Yes, what slicer and what version.

The minimum timing parameter in cura *only* affects print speed for a given layer. Nothing else.

Are you absolutely sure there is no retraction? In cura you can see it in the gcode view - if there is retraction, the blue line has a little straight-up line at the moment where it retracts.

As far as that final glob is concerned - the problem is more that the nozzle never really leaves that spot. One way to fix that is to add a seperate throw-away tower next to your print so the nozzle keeps going over there to let your part cool. This will also increase stringing (which can be fixed usually by lowering temperature).

Stringing is easily fixed afterwards but if you want it to look perfect without cleanup - well here's more info (doesn't work for all types of PLA though):

http://umforum.ultimaker.com/index.php?/topic/1872-some-calibration-photographs/

 

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Hey guys thanks for your response.

I've got to be honest, I am woefully ignorant of slicers, to the point where I don't even know what I am using currently. I am using Cura 13.06, and when I need to print pieces with support material, I use Daid's Cura 13.07 SupportTest2. Before last week, I had no idea options of different slicers were available. I have simply been loading my .stl files into Cura, letting it render, and printing from there. I haven't really noticed any problems before this last print, but it could also be that I am becoming more in tune with the process and noticing more.

I know this doesn't give you guys much to work with, but I'm totally ready to learn with a bit of guidance. How can I check what my slicer is? Does it have anything to do with the Marlin firmware that I recently installed? How can I install other slicers to try them out in conjunction with the Cura software, or is Cura my slicer?

As always, thanks for reading. I appreciate the help and support of this community!

Luc

 

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And yes, gr5, I am sure that those long beads 4 inches across the top of my part are done so with no retraction. I can at least identify what retraction stringiness looks like, as well as the sound of the extruder retracting. During those final moments of the pipe print, the print head made no stop before retraction, no extruder noise for the retraction, and the bead was not stringy. It was a complete, and rather well laid (for being printed into the air) line, complete from start to finish. Retraction strings usually trail off.

 

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Okay so I've only used Cura so I'm not an expert but here's a little background:

Cura was written by David Braam (Daid on this forum) and is the GUI portion that interacts with a slicer called steamEngine.

Cura is written in the python language. steamEngine written in c. steamEngine was also written by Daid.

When you go back a few months, Cura used a slicer called um. Damn I forget! Slic3r maybe? This slicer was not written by Daid. It is about 100X slower than steamEngine but is very useful. Usually takes less than a minute to slice a model. But sometimes it takes hours. You can try it out by downloading cura 13.04.x (or older but why would you?).

Daid is doing a great job with steamEngine but it feels like he put all the dual extrusion issues at the top of his huge list of featuers/bugs for steamEngine. Right now he seems to be working on support (physical support).

Another great slicer to try is kisslicer. It's free and has a great gui just like Cura. It's at kisslicer.com.

Another popular slicer is netfabb. This is I beleive what professionals use (and pay for).

 

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Yes, Cura is your slicer, to all intents and purposes. Behind the scenes, in versions up to 13.04, Cura was using Skeinforge to do the slicing. In 13.05 and later, Cura uses new custom code ('SteamEngine') to do the actual slicing. But the two can't really be separated, so most people just talk about 'Cura' as being the slicer.

Slic3r and Kisslicer are two other free options for slicing. Use one or other of those instead of Cura. Repetier Host is also free, and provides its own front end for managing the slicing (and a good tool for viewing and visualizing the results from gcode), but actually uses Slic3r as the backend to do the actual gcode generation.

Cura/SteamEngine is still under very active development, and has some quirks. The path planning in particular is a little odd at present, so that's probably why you are seeing oddities. In particular it doesn't do retraction when moving across what it thinks is the 'inside' of an object. Maybe that is what is causing your stringing.

If you want to share the gcode for a print that's causing you issues, I'd be happy to look at it, and see what might be going on.

 

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As Gr5 pointed out there is another option called NetFabb, which is the slicer I use. I just wanted to write about it here for completeness.

NetFabb is a commercial application that is designed to work with the big (expensive) professional 3d printers like the Statasys machines, etc. However, they've also added some support for a handful of hobby/consumer printers like the Ultimaker. When you buy a license for NetFabb you get the basic software plus an 'Engine' for the specific printer that you are using. Because NetFabb is targeted at the comercial printers it has lots of advanced features that are not found in the free slicers.

Back when I first got my Ultimaker it was before Cura was available. The de-facto standard at the time was a program called Replicator-G, which used Skeinforge as it's back end. There were serious problems with Replicator-G and Skeingforge... They were VERY slow, tended to crash on large models, and generally produced pretty poor surface finish on the printed objects. The only viable alternative at the time was NetFabb and people were showing off some amazing prints that they had done with NetFabb that just were not possible with Rep-G. That's why I bought it.

However, since Cura has come about with it's new SteamEngine the advantage of NetFabb is much less than it used to be. The focus of Cura is simplicity and ease of use so it probably will never support many of the advanced features of NetFabb.... But really, most people will never need those features.

Here are some of features of NetFabb that you won't find in Cura (yet):

- Concentric fill on top/bottom surfaces (instead of crosshatched lines back and forth it does circular fill). Also can do crosshatch fill.

- Configurable different speeds and line thickness for outer shells and inner shells... So you can print your outer facing side slow to get high-quality and then print the inner shells faster.

- Configure the fan to turn off and on at different heights

- Create regions in your model that can have different settings. I.e. Print slower in a certain part of the model and faster in another part. Also control the infill density in different regions so some parts can be hollow or sparse infill and others more solid.

- Because you change the line thickness of your shells and infill separately you can use very thick infill lines to make parts really strong.

- Half-height slicing... Lets you slice at twice your print height resolution and perform a sort of 'interpolation' in between to improve quality... The default 'Ultra' Profile is 0.08mm layer height, but because of this feature it really is more like 0.04mm.

You can see some of my prints that show these features here:

https://picasaweb.google.com/102544598518008997408/3dPrints?authuser=0&feat=directlink

Most of those prints were done with NetFabb.

However.... NetFabb is a commercial product and their commercial clients come first... They are very slow at adding features and fixing bugs on the Ultimaker engine. They took ages to change their calculation engine to Volumetric after that had become the standard approach on Ultimaker.... and although NetFabb always had an option in it's configuration for retraction, this never really worked on the Ultimaker Engine... It took them almost a year to fix that. It also works on Dual Extrusion, but I think there are some bugs with retraction when doing dual extrusion (I haven't played with it enough yet to be sure)... but I don't think these bugs will be fixed any time soon.

And it's very expensive at €150. You can buy it in the Ultimaker shop if you are interested... but after all that, my suggestion is to stick with Cura. It's come a long ways.... And though it's not quite as advanced as NetFabb, it is free and pretty damn close in the quality you can get. I still stick with NetFabb because I like it and I paid for it... but now I think it's not worth the price and Cura gives you a lot of functionality, is easier to use, and best of all it's FREE.

Cheers,

Troy.

 

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Wow guys. Awesome responses! There's some pretty good information in here.

@gr5: Yes, Cura retraction was enabled. I've got 40mm/s retraction, 4.5mm distance.

@Code Maven: Honestly, those features sound SO useful. I'd love to vary my shell thickness, temp, and fill throughout parts. I've already had a print in which I was wishing for this kind of control. But like you said, Cura is free and works pretty darn well.

@Illuminarti: I am going to reprint this pipe and check for more string problems. From gr5's advice, I'm going to drop the temp on that print by 10 degrees and see what happens. I had bumped it up to about 100 mm/s, and I wanted to make sure I wasn't underextruding, so I think I may have gone a bit on the warm end of things at 230C. After I print again around 210-215C, I'll come back here and confirm whether or not the gcode was messing up and drawing lines where it shouldn't have been.

Again, thanks so much for reading and your insightful responses guys. It's this kind of support that makes me so glad I purchased an Ultimaker!

Regards,

Luc

 

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1) If you really care about stringing so much, do a test print like I did here. It only takes a few minutes to run the test itself. Keep good notes as you change the temperature. I found that different color filaments have hugely different results:

http://umforum.ultimaker.com/index.php?/topic/1872-some-calibration-photographs/

2) If you go lower temp you need to go lower speed (volume actually). So if your layer height is .2 and your temp drops to 210 or lower, now you really should slow down to at least 50mm or lower.

3) If you want the features of netfabb but don't want to have to learn it's quirks, learn how to use existing (and write new) cura plugins. These can very easily do things like change speed or temp at a particular layer. Adding fill you can't do but it's not too hard to remove all infill for a given layer.

>I'll come back here and confirm whether or not the gcode was messing up and drawing lines where it shouldn't have been.

I believe Illuminarti offered to check the gcode for you if you send it to him. I think he uses repetier host.

Or you can check yourself in just a few seconds. Slice it again and view in cura in slice view. Pay attention to all blue lines. Wherever retraction occurs you can see the blue lines move vertically and not just horizontally - there is a little vertical line - maybe 2mm high? That is a visual representation of retraction.

 

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I just checked the layering in Cura, both the 13.06.4 and 13.07 TestSupport2, and I looked for the little vertical blue line indicating retraction.

Apparently Daid's 13.07 does not support certain retractions that 13.06.4 does. I checked both programs, and the 13.06.4 does show a retraction before the move - 13.07 does not. I do all pieces with excessive support material in Daid's 13.07 because it makes cleanup a million times more simple, but it seems to not be quite as polished as of yet.

This explains my dilemma. I suppose for now I can just deal with cleaning up these excessive stringers. It's just good to know my intuition was correct. Some parts were stringy, but the bad ones were full extrusions in mid air.

Thanks for your suggestions gr5! It really helped me figure this out.

Luc

 

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Actually.... no. There are three different ways that you can get 'strings':

1) The print head retracts before moving, but some trail of plastic gets pulled behind the head anyway.

2) The print head doesn't retract before it moves, and so any residual pressure causes it to ooze somewhat during the move.

3) The printer actively turns the extruder motor, and extrudes plastic while moving over space.

Even in your worst case scenario, Luc, I think you're only seeing the first two of these - so not 'full extrusions in mid air'. Just pent-up pressure being released. The third one would typically be some sort of slicer bug (except in the cases where you are intentionally bridging over a gap).

 

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@daid - what does that do exactly? Does it reduce the extrusion for the last mm of XY travel/printing maybe? Or does it stop extruding completely the last 1mm of xy travel? Or maybe the last 1mm of filament is underextruded?

#2 above will show as a blue line without the vertical blue line. #2 can be reduced if you lower the printing speed (because pressure in print head is lower).

 

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