Why so slow?  

RE: Why so slow?

Actually the default MK3 settings are pretty fast for my taste. In general printing faster means a lot of disadvantages. Like:

• Higher risk for fail
• worse adhesion between layers
• artifacts/ghosting
• Higher wear and tear of the hardware
• Filament might not support this speed
• ...

Usually if I need to print something faster, I increase the layer height or go with thicker nozzle diameter.

RE: Why so slow?

Counterpoints:

1. I haven't found a higher risk of failure, but I do have part adhesion completely under control unlike many users (I use glue stick)

2. I haven't found worse adhesion between layers, but I haven't tried to quantify it. If adhesion is worse it is most likely because of temperature sag under increased flow volume - reducing maximum volumetric flow, slightly increasing temperature, and/or tuning PIDs should solve it.

3. I haven't noticed worse artifacts/ghosting. In fact, speeding up can potentially smooth out inconsistent extrusion problems, as was noted by another user in a recent /r/prusa3d reddit thread. The reason for this is that there's a slight delay in the response between the extruder motor pushing on the filament and a change in nozzle flow rate. This is why linear advance is needed, and it can also work to our advantage here.

4. I wouldn't imagine increased wear would be too significant. Travel moves do already use the speeds I'm talking about. I would expect higher acceleration limits to have a larger effect on wear. However, if you are using smaller layer heights, there will of course be more moves before your print is done, therefore increasing wear proportionally. I've printed like this for *years* on previous machines, going through tens of spools of filament, with no maintenance or replacement of mechanical parts beyond re-tightening belts, and as far as I know those machines are chugging happily away printing stuff for their new owners.

5. There is a maximum volumetric speed setting for each filament. Reduce it as needed.

I've found that increasing layer height beyond 0.2 often leads to unacceptably weak parts, especially ones with thin vertical walls. I personally won't be going up on nozzle size unless I buy a second printer. Changing nozzles back and forth and re-doing offset adjustment on a print-by-print basis is just too much effort.

RE: Why so slow?

it might be different if the print bed has a full load on it. I find myself turning the dial to around 175% often with lighter loads.  the next time I fill the printbed ill see how it looks at the faster speeds.  I don't fill it often, so it might be awhile for that science

RE: Why so slow?

Posted by: jschall

In general, I find that I am able to crank my tuning print speed multiplier to around 300% on the first layer (at least when printing with PLA) and pretty much all the way to maximum (which appears to maintain reasonable acceleration limits and volumetric extrusion limits) on other layers with little-to-no realistically perceptible loss of quality. i.e., it is totally fine for 99% of prints that I do (granted, mostly mechanical parts and not miniatures or whatever).

You are getting excited about speed, and speed is an illusion. Your results going to depend on your part complexity and size. On a small or detailed part, the printer rarely gets up to full speed so prints at a fraction of what you've specified. If the actual print speed is 30mm/s and you crank it up 300%, you're still only at 90mm/s. You're also not free from real-world physical constraints like acceleration and jerk, so that 30mm/s may be the maximum speed you hit printing a particular feature. So yes, you can print some things successfully at "300%" whatever that is, but a real test would be printing a variety of things, large and small, simple and complex, at faster speeds. And documenting the results.

Linear speed is a 2D concept. That's how fast you're able to move that nozzle from point A to point B. Using that as a measure of "print speed" is meaningless unless you can also successfully extrude plastic during those moves. 3D printing requires thinking in 3 dimensions. You're not only trying to zip that nozzle along, but you're also trying to lay down an extrusion that has width and height as well as the length of your movement. At some point, you're going to run into the maximum throughput limitation of your hotend (unless you really think you've got one with infinite capacity). The E3D V6 hotend used on the Prusa i3 Mk3 is rated to roughly 15mm^3/s. Specifics vary depending on temps, nozzle and material, but a working figure of 11.5mm^3/s is realistic. That means, no matter how "fast" you zip that nozzle around, you're not going to be able to push somewhere in the neighborhood of 10-20mm^3 of plastic per second. This is expressed as Maximum volumetric speed (MVS) in PrusaSlicer. Exceed MVS and you start to get extruder clicks, bucks, skips and jams. It's a mechanical process subject to physical limitations. No surprise there.

MVS is calculated as Speed X Layer Height X Extrusion Width.  This means with a 0.40mm nozzle, you can print at up to roughly 120mm/s using a 0.40mm nozzle with a layer height of 0.20mm and extrusion width of 0.48mm before you run into problems. You didn't bother to document your testing before declaring complete victory, so we can only make assumptions, but I suspect that 300% setting was still printing mostly at speeds within the MVS capacity of your hotend. You also didn't bother to show results for ringing and surface quality. That's a bit like taking a rental car out on a motocross track and declaring it's a good off-road vehicle. It works, but it's not recommended.

For my money, I would bet that for the vast majority of prints, more quality can be had in the same amount of time by reducing layer heights and increasing speeds. Reducing layer height (to a point) dramatically improves part strength, overhang capability, visual smoothness etc. My go-to layer height is 0.15mm for general use.

A lower layer height is going to markedly slow down print times, so now you're working at cross-purposes. Do you want to finish prints more quickly, or just watch that nozzle zipping around? Because if you want to finish faster, you have to lay down more plastic in a given amount of time. That can be accomplished with larger layer heights, but also with wider extrusions. Using a larger nozzle, you can print wider and higher (if desired) at slower speeds and still finish up much more quickly.

So why are the PrusaSlicer presets so slow? Even the "speed" and "draft" presets are dog slow.

Because they are intended to yield usable results under a variety of conditions. Again, you did not show your work, so assuming you've stumbled onto something that has eluded the 3D printing community for years may be a bit premature.

Additionally, I've found that in PrusaSlicer/Slic3r, it is very difficult to optimize for speed. Generally I get the best results by just cranking the tuning speed. Of course, this messes up anything that legitimately needs to be slower, such as first layer. I made one issue I noticed here:  https://github.com/prusa3d/PrusaSlicer/issues/2480

You are more than welcome to change them, and you can maintain a lot more control if you give up spinning the knob in favor of more precise settings in the slicer. Understand, though, that PrusaSlicer (and the better slicers out there) use and maintain MVS. Look under Filament and Print settings. If, for some reason, you want to get faster prints, you'll need to increase the MVS throttling along with setting your higher print speeds. Your hotend still has the same limitations though, so beware skips & jams if you do this.

Have fun with it, and do what you like, but there are perfectly good reasons for most of the recommendations if you care to ask!

Or to quote Thulsa Doom from the local makerspace...

Ah. It must have been when I was younger. There was a time, boy, when I searched for [speed], when [speed] meant more to me than gold or jewels. […] Yes! You know what it is, don’t you boy? Shall I tell you? It’s the least I can do. [Speed] isn’t [fast], boy, [volumetric throughput] is [faster]! […] That is [speed], boy! That is power! What is [speed] compared to the [nozzle] that [extrudes] it? - Thulsa Doom in Conan the Barbarian after a long night in the MakerSpace

RE: Why so slow?

I appreciate that you're trying to teach me something using colorful metaphors and so on, but you're not really listening first. I am under no delusions that changing the print speed to 300% reduces the print time to 33% of the original print time. I literally said in my original post that it appears to keep the volumetric speed and acceleration under control. I'm not "declaring victory," I'm saying that:

1. The default settings can probably be sped up dramatically with little-to-no loss in quality.

2. Given a fixed time budget, I would prefer to minimize layer height over minimizing speed as layer height is the single biggest determining factor in quality, including through-layer part strength, overhang capability, visual smoothness and bridging capability.

In fact, I'm not even convinced that the maximum linear speed even makes the tiniest lick of difference in quality, since the speed in locations where quality matters such as curves with small radii is constrained by acceleration limits anyway.

A lower layer height is going to markedly slow down print times, so now you're working at cross-purposes. Do you want to finish prints more quickly, or just watch that nozzle zipping around? Because if you want to finish faster, you have to lay down more plastic in a given amount of time. That can be accomplished with larger layer heights, but also with wider extrusions. Using a larger nozzle, you can print wider and higher (if desired) at slower speeds and still finish up much more quickly.

I am *not* suggesting using a lower layer height than is necessary to get an acceptable level of quality for a given print. I am simply pointing out that there is a trade-off between speed, layer height and time. If you increase speed, you gain time that you can spend on layer height and get probably better net quality. Or, you can just take the time that you gain and run. Currently, the default settings don't make this trade-off in a way that I like and there seem to be bugs (such as the one I reported and linked above) in PrusaSlicer that make it difficult to tune the speed settings with satisfactory results.

RE: Why so slow?

Edit: I've given up trying to figure out what this stupid forum software wants to keep uploaded images from appearing distorted. Right-click and do Open image in new tab to see the undistorted images. Will host images off-site until they fix this nonsense.

Looking at your github issue, it looks like your question is why you're getting certain results with gap fill. I am getting the expected higher speeds with different settings. First, your part sliced with my settings showing gap fill in white:

Next my speed results:

The gap fill is being printed at much slower speeds than the surrounding walls. Next my overly-optimistic speed settings:

Finally, the same print with only Filament settings->Max volumetric speed set to 8 (from the PLA default of 15). No changes made to speed settings. Note that top speeds have been capped to respect MVS but the gap fill and slower speeds are still as fast as my setting. No need to change overall speeds or artificially set limits. MVS keeps it all within the limits of the hotend:

So you can certainly achieve higher speeds by calibrating MVS to your nozzle, material and temp preferences. The defaults are "safe" for most cases. There is still an upper limit though. If you're placing a constraint of a 0.40mm nozzle with 0.15mm layer heights, that's about 275mm/s, at which point the printer limit probably start to come into play (especially slinging the bed around), so expect ringing. The filament itself also has limits. Some guys did a deep-dive on max speeds last year (now lost to the winds thanks to crappy search) and found that things go downhill at about 300mm/s, largely due to the limits of current filaments. There are "high speed" filaments, but they tend to be rated to 200mm/s. The industry and technology is young.

RE: Why so slow?

Interesting. Why do you think your results are different?

RE: Why so slow?

Posted by: jschall

Interesting. Why do you think your results are different?

Made some edits at the bottom you might want to review...

There are some settings that impact speed that aren't immediately obvious. Those for minimum layer time can come into play (see Filament settings->cooling). I'll dig through your 3MF later to see if I can pinpoint the issue.

RE: Why so slow?

I see. If I change the other speeds from 0 (which is supposed to be "auto," which is supposed to respect the volumetric speed limit) to 160 as you did, it works.

RE: Why so slow?

How is a filament rated to a linear speed? I would imagine the filament would only have an effect on volumetric speed?

RE: Why so slow?

Well, thanks for helping me understand that issue.

My original reply to you is stuck in a moderation queue for some reason. Not sure if you can see it or not. Anyway, the gist is that I am under no delusion that my printer has broken the laws of physics, and I am not suggesting using a lower layer height than is necessary to get an acceptable level of quality for a given print. I am simply pointing out that there is a trade-off between speed, layer height and time. If you increase speed, you gain time that you can spend on layer height and get probably better net quality. Or, you can just take the time that you gain and run. Currently, the default settings don't make this trade-off in a way that I like.

Are there firmware limits on acceleration and speed? What are they? What are the physical limits (i.e. as determined by input voltage and motor constant?)

RE: Why so slow?

Posted by: jschall

I see. If I change the other speeds from 0 (which is supposed to be "auto," which is supposed to respect the volumetric speed limit) to 160 as you did, it works.

I had no real success using the 0 auto speed settings. I've had very good luck using 0 for extrusion widths however. I haven't really investigated the speed issue or why auto isn't working. Do note that MVS is respected regardless of whether you're using autospeed or not. MVS -- either for filament or print settings -- places an upper limit on speeds. The slicer will use your specified speeds up to the point at which MVS is exceeded, at which time it will throttle speeds to keep MVS within bounds.

RE: Why so slow?

Posted by: jschall

How is a filament rated to a linear speed? I would imagine the filament would only have an effect on volumetric speed?

It's more that linear speed is one of 3 factors for calculating MVS. This is why I say that you have to think in 3 dimensions, of which linear speed is only one. (That's also the joke reference in my signature.) Different filaments have different consistency and characteristics, so will have a different MVS value that works with your hotend. Prusa's default for PLA MVS is 15mm^3/s (which is a tad high in my testing) and PETG is 8mm^3/s. The worst case I've encountered was Colorfabb XT-CF20 which works best at 1mm^3/s. So if you're using a more viscous filament, you must either limit speeds, or change layer height and/or extrusion widths. The MVS speed limit is always enforced! (By physics. You get clicks, bucks and jams otherwise.)

RE: Why so slow?

Posted by: jschall

Well, thanks for helping me understand that issue.

No worries. I've learned a lot from this community and the reddit mob myself. Hopefully I won't lead you astray. I'm always learning myself.

My original reply to you is stuck in a moderation queue for some reason. Not sure if you can see it or not. Anyway, the gist is that I am under no delusion that my printer has broken the laws of physics, and I am not suggesting using a lower layer height than is necessary to get an acceptable level of quality for a given print. I am simply pointing out that there is a trade-off between speed, layer height and time.

Oh agreed 100%. Your reddit post had more detail, so I came back here and clarified based on that. 3D printing requires considering all 3 dimensions (well, speed and 2 dimensions) together to make any meaningful findings.

We get the occasional poster that is all excited that they've "discovered" something, only to be disappointed when reality rears its ugly head. Just wanted to moderate expectations a bit.

I watched Stefan's YouTube video and his results are interesting. I do think more testing of different kinds of stress are important (crushing, etc.) so I'm not on board with only 0.15mm layer heights just yet. My casual results favor thicker (and wider) extrusions, but I haven't done anything so thorough.

If you increase speed, you gain time that you can spend on layer height and get probably better net quality. Or, you can just take the time that you gain and run. Currently, the default settings don't make this trade-off in a way that I like.

Hmm. Well, you can print at up to the MVS of your hotend. That is calculated as the combination of Speed X Layer Height X Extrusion Width. So yeah, you can play with settings up to a point, and with a 0.40mm you can go quite fast before you hit the limit. But the limit is there. If you do hit it, one of the 3 has to give.

I do think you're going to find that different filament behaves very differently at different speeds. I see a real change in glossiness from printing at 25mm/s and 40mm/s for example. I'm sure adhesion and other considerations come into play. Unfortunately, you pretty much have to test each filament, as results with one don't necessarily translate to another. Again, there was a really great "maximum speed" thread on the old forums. I don't recall all the details, but basically, approaching 300mm/s and you got into big problems, even with a higher capacity hotend. Where the big hotends come into their own is with the big nozzles where you can push big fat extrusions at 60-100mm/s. "Speed" is definitely an illusion. "Time" is what you want to focus on.

Are there firmware limits on acceleration and speed? What are they? What are the physical limits (i.e. as determined by input voltage and motor constant?)

Yes, there are, but you can set most of them in PrusaSlicer in the machine limits under Printer Settings. The defaults provide by Prusa are "quality" or "speed" to give most users reasonable quality reliably. You can definitely tune them for speed and quality beyond that. I've got settings that (IMO) produce far better finish and still maintain good speeds, but they might not work for everyone.

Keep in mind, your Y axis involves slinging that heavy bed around, so the mechanical limits of the i3 design come into play more in that axis than along X. Finding good test prints and procedures is half the fun!