Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s  

RE: Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s

Some PLA doesn't even do well at 8 mm3/s ... that's why it's a setting the user can change.  But 99% of the time the 15 mm3/s is fine.

RE: Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s

Much of the time, you'll never see the problem, especially if you print smaller parts. Where it comes into play is on larger parts where the nozzle comes up to full speed, especially in those features where Prusa has set very aggressive speeds (e.g. infill @ 200mm/s) where I've often experienced the nozzle scraping on infill that isn't properly extruded, and large areas of solid infill where pillowing can occur. I usually adjust it as necessary for each filament (under Filament Settings->Advanced->Print speed override) but it can pop up if I use one of the Prusa default filaments. Just to be safe, I set a "maximum speed limit" for each Print Settings profile (under Print Settings->Speed->Autospeed (advanced) of 11.5mm^3/s. The page linked by the OP gives a full set of notes. I've found this is also the key to success with hard-to-print materials (e.g. flexibles, filled materials) are quite viscous and do best when printed slowly. Prusa does make adjustments for PETG and others, but PLA at 15mm^3/s is problematic in some situations.

RE: Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s

No arguments ... only observations. 

In a few prints late last year, infill was an issue because of print speed and lack of proper "volume" adjustment: rectilinear infill is not building on the prior layer since it alternates fill directions between layers.  Increasing the extrusion width addresses the issue, so that the filament has a contact point and is better supported, not pulling apart as the extruder races along.  0.65 mm width seems to be a good number for infill when printing 0.15 mm layers (about 150% the extrusion volume); 0.55 when printing 0.10 mm layers.  This leaves a bit thinner infill stack, but one that is stable and not subject to broken raspy hooks.  It also doesn't make the same bump and grind that grid infill causes on large surfaces.

Agreed 15 mm3/s is probably too high; but then E3D has a data sheet listing the SuperVolcano at 110 mm3/s with an 80w heater. Can't find a similar spec for the Volcano or V6.  It would be interesting if anyone has something officially from E3D on the subject.  Default Settings:MoveAxis:E seems to arrive at only 4 mm3/s ... and doesn't press the volume limit.

Maybe the time to build a test part ... lol.

RE: Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s

Posted by: Tim

[...] Agreed 15 mm3/s is probably too high; but then E3D has a data sheet listing the SuperVolcano at 110 mm3/s with an 80w heater. Can't find a similar spec for the Volcano or V6.  It would be interesting if anyone has something officially from E3D on the subject.  

I did find one reference to 15mm^3/s from E3D but it wasn't easy to find and I can't seem to find the link. The 11.5mm^3/s is cited in a lot of reprap and general discussion threads. Part of the problem is that there doesn't seem to be a consistent name for this specification.

I've erred on the side of caution and tried to stay below at known-good values for my profiles. There is a simple procedure to calculate it manually that I have not completed. Essentially, start shoving filament at faster rates until you get extruder skips. Back off the speed a bit and multiply by layer height & extrusion width to get the "magic value" for your specific hotend. You'd have to print a large part to get an absolute value for each filament. Using a larger nozzle should provide quick results. May try this for my next project.

Maybe the time to build a test part ... lol.

Hah. Well, I can do that easily enough. Scale this project up enough to hit maximums, tweak speeds at each level and listen for the nasty extruder noises. It'll be a long and boring print though!

RE: Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s

Posted by: Tim

[...] Maybe the time to build a test part ... lol.

Looks like 60x60mm will allow infill speeds to hit 200mm/s.

I've attached the STL. I won't be able to do more for a day or so. I'm thinking mounting a 0.60mm nozzle with PLA should yield good results. Do a bit of test to destruction and see what happens. I think I'll mount one of my crappy generic brass nozzles for this. I feel like I'm cutting the seatbelts and disabling the airbags for this one...

RE: Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s

I did a couple tests.  Nothing concrete yet, but interesting for preliminary tests.

25 mm3/s was a non-starter.  15 mm3/s showed no almost no issues until a couple mm up in the build inter-layer adhesion started to wane.  

RE: Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s

Posted by: Tim

And just caught the 15 mm3/s @ 50 mm/s was actually only 9 mm3/s ... oops.

Definitely more practical than mine! I've been looking into calibration based on free-air calibration, but the math starts to make my head hurt. Your approach looks much simpler. Doing some long boring adhesion tests on the textured PEI this evening, but will try to look more tomorrow. I did find that some PLAs are the ideal. Other materials need to have MVS reduced from there. I'm sure 11.5mm^3/s is a bit on the conservative side and you can probably beat that with some additional heat, but I think it's a good starting upper limit.

RE: Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s

Only one of the 15 mm3/s strips was misrepresented. All the others are correct, as are the 18.7 and 20 mm3/s strips.

I'm thinking 15 mm3/s is a good start.  My test shows it's where plastic is laid down well at three speeds.  The extruder has no issues at all; only at 20 does the extruder really complain.  Plus, I can print 18 without too much trouble just by keeping the speed down.   

Trying to rethink my test to make multiple layers; but want a good first layer to build on.  I want to understand why that top layer is scuffing off... but then I really don't know what the true E feed rate is on that grid pattern. The math shows it probably isn't 15 mm3/s - (0.2*0.45*100=9mm3) - it seems like the strokes were a slightly less than a second, though I wasn't timing it. Then again, with accel/decel, at 200 mm/s peak, maybe. And the upper layer that was scuffing was also about where the temps start to be cooler, and with a 210 nozzle, cool plastic, 15 mm3/s may be at some adhesion threshold.  But that isn't an extruder issue and much as selecting a better temperature set.

RE: Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s

OK, I got my head around the free air extrusion tests. I like free air tests over prints because acceleration values, XY motion and print parameters don't come into play.

1. I'm printing with filament with a nominal diameter of 1.75mm
2. The area of the cross-section of that filament is roughly 2.405mm

With that in mind, I fired up Pronterface, set extruder mode to relative and set my nozzle temp to 200C and began extruding using eSun PLA+:

M83
M109 S200

I then began issuing commands to extrude 60mm of filament at different speeds:

G1 E60 F300
G1 E60 F400

Once the extruder started clicking, I backed off until I found a speed that consistently didn't click. Results varied significantly by nozzle temperature:

• At 195C E365 was safe (~6.08mm/s * 2.405 = ~14.62mm^3/s)
• At 200C E400 was safe (~6.67mm/s * 2.405 = ~16.04mm^3/s)
• At 210C E450 was safe (~7.5mm/s * 2.405 = ~18.04mm^3/s)

So far, this matches my previous experience:

• At 195C, 15mm^3/s is a bit too aggressive.
• Raising temps increases throughput, but at the risk of diminishing print quality.
• This testing was done with an E3D nickel-plated copper nozzle which is supposed to provide superior thermal characteristics to plain brass.
• Ambient temps will likely affect results. I'm doing this testing at 68F/20C during a surprisingly chilly New England night.
• eSun PLA+ is a very smooth printing filament.

For now, though, I'm comfortable saying 15mm^3/s is not safe for all PLAs and 11.5mm^3/s is a good safe default to avoid problems for most users. This is borne out (unscientifically) by a number of posts that popped up over the summer months in which users reported failures printing with PLA (at 15mm^3/s) but none with PETG (8mm^3/s). My advice for extruder click and jams problems is always slow down, and that fixes many of these problems. Setting a lower MVS value just does that without a lot of fiddling with speeds as has to be done with lesser slicers (not KISSlicer - PJR!).

Additional testing to be done:

• Compare results with different nozzle sizes & materials. (Lots of people having issues with filled materials. Does this test work satisfactorily to identify MVS for different filaments? I think so, but I'm sleepy. Do different nozzle sizes change the equation?)
• Compare results at different ambient temps.
• Compare results using that toxic non-name filament we all have stuck in the corners.

Of course, there's a high probability I'm wrong. If you like to dissect posts (you know who you are!) to point out any misconceptions or problems, this is a good one for it. I'm dusting off skills I haven't used much in 30+ years, so lots of rust may have creeped in. I spent more time writing this post than actual testing, so YMMV!

I now have a pile of filament spaghetti I need to police up.

RE: Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s

One last note (curse you stupidly short edit time!):

• I'm running an OG R2 (? - April 2018) extruder setup. I wouldn't expect cooling to impact results much, but should verify across a range of Prusa configurations.

I'd also be curious to see how use of MMU2 affects temperature selections. Lots of variables!

RE: Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s

Belay most of what I just said - copied from the wrong column on the slower speeds...  Extruder definitely grinds above 15 mm3/s.  But the extruder is spitting out 15 mm3/s without too much trouble.  I may limit further tests to 15 mm3/s, too, because I'm thinking tests have established it is a practical maximum. 

New test coming. But I need to rethink order: fast to slow as I have been doing has drawbacks (grinding filament makes next pass stutter). 

RE: Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s

Posted by: Tim

Belay most of what I just said - copied from the wrong column on the slower speeds...  Extruder definitely grinds above 15 mm3/s.  But the extruder is spitting out 15 mm3/s without too much trouble.  I may limit further tests to 15 mm3/s, too, because I'm thinking tests have established it is a practical maximum. 

Curious to see what impact nozzle size and composition, temp and filament have on your tests. I'll be interested to compare results with our different methodologies as well. This is definitely that's something of a dark art, and only Slic3r and KISSlicer seem to even be aware of it*. Other slicers just leave you twiddling speed, living with worst-case settings or being overly-optimistic and running into problems on larger prints.

Agreed with 15mm^3/s as a maximum -- at least so far as recommendations to others -- since that's E3D's stated max for the V6 hotend. I'm sure they built in a bit of slop to account for variations in production.

* Although I did come across one reference to an ancient version of Cura that allowed entry under the extruder settings.

RE: Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s

Your copper nozzle may explain why you are getting 18 mm3/s ... I was grinding at 17 mm3/s after 3/4 the pass. Which points to thermal mass being depleted. 

I need some sleep to mull over how best to test tomorrow.  I should ask a mod to come in and delete all the garbage I posted above.  It's embarrassing 8^( .  Sucks we have to make our own emojis in this forum, too.

RE: Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s

Posted by: Tim

Your copper nozzle may explain why you are getting 18 mm3/s ... I was grinding at 17 mm3/s after 3/4 the pass. Which points to thermal mass being depleted. 

Reassuring to at least be in the same ballpark. At some point, I want to match our setups to do some like-by-like comparisons.

I'm looking forward to more testing:

• Different nozzle sizes.
• Different nozzle composition.
• Testing P3-D claims of improvements.
• Comparing P3-D versus E3D versus others.
• Comparing those cheap AliExpress wonder-nozzles.
• Oooh, titanium heatbreaks and stuff ... though perhaps not. That stupid Prusa heatbreak step though?

It would be great if we could get someone with a copper heat block to test and contribute findings. 

I need some sleep to mull over how best to test tomorrow.  I should ask a mod to come in and delete all the garbage I posted above.  It's embarrassing 8^( .  Sucks we have to make our own emojis in this forum, too.

The inability to edit really keeps us from putting together coherent posts. I'm going to start composing in another editor, then just pasting after I've proofed everything. It's nice to have a methodology that can be used with non-E3D hotends as well.

Of course, the Volcano and Super Volcano guys will be laughing at us, but we're racing the midget cars!

RE: Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s

I formalized my process a bit, starting high and decreasing by 50 until clicks stopped, then working upwards by 10s until it clicked, then down by 5s. When I found a good temp, I repeated 2 more tests for a total of 3. If I could feed 60mm of filament with 0 audible clicks, I went with that value. Quick results after swapping an E3D plain brass nozzle in:

• At 195C E395 was safe (~6.58mm/s * 2.405 = ~15.82mm^3/s)
• At 200C E420 was safe (~7.00mm/s * 2.405 = ~16.83mm^3/s)
• At 210C E450 was safe (~7.50mm/s * 2.405 = ~18.03mm^3/s)

A little surprising. I was expecting the E3D nickel-plated copper to perform better. Will continue testing others. I'm really interested to see how the P3-D Apollo nozzle fares as it claims much better thermal performance.

 I'll have to repeat my prior tests with the same rigor for consistency. There's a wee bit of padding in the 15mm^3/s Prusa default for PLA under simple test conditions, but I still think it's a little too close for comfort. This may explain why Prusa's PLA defaults tend to be in the 210-215C range which is considered hot for PLA.

RE: Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s

Bob - what acceleration and max feed are you using with the E395 command?  Or is that short hand for E60 F395?  But question remains for acceleration.

Also - at what temp did you run PID calibration?

RE: Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s

Hey, bobstro, I looked at your MuppetLabs just now about calibrating new filament. I've been thinking that I should add figuring out volumetric flow based on your topics above. But my disagreement is with your order (though, the reasons for my disagreement may be based on new information discovered here that you may not have had last time you edited your page). Because it seems extruder temperature (and probably nozzle, but that just muddies the water for the moment) affects the max volumentric speed, I would find the max volumetric speed after doing a temperature tower and I've decided on a temperature that has the best compromise for surface finish, overhangs, stringing, bridging, etc.

Up until now, based on your pre-experimenting thoughts (I'm thinking that "advise" is too strong a word), I was assuming that your 11.5mm³/s wasn't conservative enough so I'd been just throwing 11mm³/s in to be even more conservative. Granted, I rarely print something large enough that I even approach the max volumetric speed on my stock 0.4mm nozzle, especially since I usually use gyroid infill which isn't really the fastest infill available... Though, not knowing how to find the max volumetric speed has been one of the reasons why I have yet to try using flexibles yet (even though I have a spool in my collection...).

I do have a question (that you might not have an answer for): What would you say is the range of amount of filament used for dialing in extrusion? How many 6cm extrusions do you end up having to do, average and maximum? A dozen? More? Less?

RE: Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s

Hi Bob @bobstro ,

you asked for an analysis, so here is the physics. 🙂 And thanks for the measured data, that kind of research is most valuable.

PLA thermal conductivity is 0.13 W/m·K, steel is around 25 W/m·K, brass is 109 W/m·K, aluminum is 205 W/m·K, copper is 385 W/m·K.

Even steel is 20x more thermally conductive than PLA and so it is always the filament that is the limiting factor in the melting process and the nozzle material doesn't make much difference. That's why the E3D Volcano, the Supervolcano and the Raise3D Matchless nozzles exist - they try to increase the contact area between the nozzle and the plastic to pump heat into the plastic faster. Even the 40W heater of the v6 is not the limiting factor. With PLA's thermal capacity of 1.8 J/g·K, fusion heat of 93 J/g and density of 1.24 g/cm³, a 40W heater could easily melt 70mm³/s of pure crystalline PLA. PLA is usually shipped in mostly amorphous form, which makes melting even easier.

In your experiments, you're basically measuring what is the limit of the nozzle → filament heat transfer. With increasing speed, the temperature of the extruded plastic decreases until it is below the melting point and the extrusion stops. Increasing the temperature of the nozzle increases the heat flux into the filament thanks to a bigger temperature gradient, but the extruded plastic temperature will be the same in all the maximum extrusion rate situations you measured, somewhere around 180 °C.  This would result in very poor layer adhesion and possibly other adverse effects.

As for the filled filaments, I limit my carbon-nylon printing to 3.6

Your findings support your original statement that a slicer limit of 11.5 mm³ would be a more reasonable default for PLA. With that, there is enough headroom for the nozzle to heat the plastic to a reasonably consistent temperature.

Fortunately, in real prints, the extrusion rate is varying considerably and it's enough for the average to be under the sustained rate limit. Acceleration and speed constraints for particular features tend to limit the print most of the time. That's why the 15 mm³ default can still work - as an infrequent stop gap to prevent the printer stalling on the quick parts of the print.

RE: Slic3r PE: Please reduce default values for "max volumetric speed" from 15 to 11.5 mm³/s

Posted by: Sembazuru

Because it seems extruder temperature (and probably nozzle, but that just muddies the water for the moment) affects the max volumentric speed, I would find the max volumetric speed after doing a temperature tower and I've decided on a temperature that has the best compromise for surface finish, overhangs, stringing, bridging, etc.

The converse is even more true: Speed changes the temperature of the extruded plastic. (See my other reply.) So when you select a particular temperature, any increase in speed will change the print quality. While there is enough headroom, the change is negligible, but as you start to approach the speed limit, the temperature of the extruded plastic will go down quickly.

So it's about finding a good combination, rather than tuning one and then the other, or vice versa, unfortunately.