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Volumetric extrusion

Posted by drmaestro 
Volumetric extrusion
April 19, 2016 05:10AM

I am trying to figure out the volumetric extrusion option present in Marlin firmware. My understanding is that the firmware calculates the volume of extruded plastic (in mm3) instead of the length (in mm). Is this method more accurate? What is the advantage? To use it, do you have to issue m200 command and also eneable it on the LCD menu or only 1 of them is enough?

Re: Volumetric extrusion
April 19, 2016 05:20AM
I'm not sure about Marlin's implementation, but I use volumetric extrusion in slic3r and enter the filament diameter via LCD on my Smoothieboard when I print a part. The main advantage is that the gcode doesn't care what the filament diameter is, so you can reprint a part using a different spool of filament without reslicing. If you enter "0" for the bed and extruder temperatures when you slice, the gcode no longer cares about the material or the diameter of the filament. You can switch between PLA, ABS, and TPU, etc., without reslicing. You then have to set temperatures and filament diameter at print time.

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Volumetric extrusion
April 19, 2016 07:03AM
So it isn't more accurate, but more convenient, altough I am not sure if that's really useful as you might have to change other parameters including printing speed, infill density, retractions, etc when changing filaments, so you would have to reslice it probably. That could work with PLA and ABS, as they would probably have similar characteristics (except temperatures).
Re: Volumetric extrusion
April 19, 2016 10:58AM
To give my 5 cents on volumetric extrusion:
I did not care at all about it as I thought with no filament sensor, always using 3mm filament and no obvious difference there would be no benefit at all.
A long time later I started with Nylon and copt all the problems that come with it.
Here I found an article about volumetric extrusion that got me thinking again as the explanations used there made much more sense.
For starters it is not really about what or how the filemant come in - it is about how it comes out winking smiley
With standard extrusion it goes like this:
Speed is fixed for a given task, like perimeter, infill...
The extrusion width is usually fixed too.
That means every time there is a change in speed or task the pressure inside the nozzle will change.
This can cause to over or under extrusion especially at new line starts.
On the other hand with volumetric extrusion the parameters are adjusted on the go to keep the nozzle pressure even.
Ok, simple:
Check how your extruder works during a print and you'll notice it changes speed (not counting retractions here).
If you do a volumetric extrusion these extruder speed changes will be kept to a minimum or in a good case be eliminated completly.

Especially complicated filaments benefit from volumetric extrusion, not just Nylon but also flex filaments.
Keep in mind though that some settings will work against each other!
For example using retractions should be avoided or limited to where it is really required.
Don't mess with the Gcode or add layer waiting times.
Be aware that you should use automatic settings for the speed, leaving a fixed speed for some moves will render the benefit of volumetric extrusion useless.
Simply keep in mind that you want to avoid everything that changes a nice and constat flow of filament.
Re: Volumetric extrusion
April 19, 2016 01:40PM
Is there a step-by-step guide to enable volumetric extrusion on the web? I get confused on which are the exact steps to follow.
Re: Volumetric extrusion
April 19, 2016 02:20PM
DownUnder - two different things. In slic3r, "Use volumetric E" on the printer settings tab is the concept that DD was describing for having the g-code use units of mm3 for the g-code extrusion commands. Firmware then does the conversion to steps based on filament diameter. The new constant pressure extrusion algorithm is the poorly UI'd Autospeed max print speed setting on the Print settings/Speed tab, in conjunction with setting the manual speeds to 0. Confusion abounds because it's close to the almost unrelated max volumetric speed box.
Re: Volumetric extrusion
April 19, 2016 08:38PM
Well I did not do any code diging on the matter all I know is that Nylon prints much better using the volumetric extrusion settings.
And if set correctly the extruder really runs at an almost constant speed throughout the print.
Re: Volumetric extrusion
April 19, 2016 11:23PM
How can the extruder run at constant speed with the motion of the extruder carriage being subjected to acceleration and deceleration for every segment?

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Volumetric extrusion
April 20, 2016 12:46AM
Hi, a couple of questios: 1, why volumetric extrusion is better for naylon? 2, in slic3r, lets say I want to print useing volumetric extrusion, useing repetier firmware, I set extrusion with mnaully (I want to do it), set speed to auto speeds and then slic3r will try to generate a steady (or somehow steady) speed along all the print?
Re: Volumetric extrusion
April 20, 2016 04:02AM
Nylon like some other plastics has a great shrinkage.
Keeping an easy nozzle pressure simply gives better results as the flow of plastic is even.
And yes if set up correctly you will see that your extruder keeps and almost completely steady speed instead of changing the speed all the time.
Re: Volumetric extrusion
April 20, 2016 06:42AM
How can the extruder run at constant speed with the motion of the extruder carriage being subjected to acceleration and deceleration for every segment?

You're right, it't not (and can't be) truly constant. The aim is to minimize the pressure swings but you can't eliminate them. For example, with traditional manual speeds it was fairly common to go from a 25 mm/s perimeter to 50 mm/s infill, often with the infill having a higher width than the perimeter. This causes a major jump in the extrusion rate and a resulting swing in the nozzle pressure. All that the constant pressure approach is doing is choosing the linear speeds to minimize changes in the extrusion rate. If all the widths are the same then all the speeds will also be the same and pressure changes are kept to a minimum - but you still have to slow down for the corners. If the widths are different then the speed is adjusted to compensate, so wider segments will be printed at a lower linear speed than thinner ones.

Nylon seems to be particularly springy, so it's very prone to over-extruding during a high to low pressure change, and under extruding in a low to high change. Minimizing the pressure changes does seem to help a lot. You don't have to use autospeed to do that of course, you can set manual speeds all the same and use the same extrusion width for all segment types and you get the same result. Autospeed just makes it easier if you do want to use different widths.
Re: Volumetric extrusion
April 20, 2016 07:19AM
Sounds what I have been looking for: I have a particular material, is a type of PET, made from recicle pet bottles. It ahs very nice features, but a "disadvantage, because it behaves like both PLA and ABS: it melts around 240/250 degrees, but starts to soften around 80/90. This low soften temperature makes really dificult to use it in an all metal hotend. The trick so ffar has been printing it at (not slower than) 60mms/s and with an extrusion width of 0.68 (to force the printer extrude materuial fast a as much as posible). So far this is my way of useing it (I know, probably someone would say that the problem is cooling in the heatbreak, but it is no, E3D has confirm that haveing the extruder at 250, will make the temperature at the heatbreak to be around 80 and that is normal and expected. But anyway I have increase cooling there with a radial fan)
So the problem is that if for some reason the extrusion slows down, like when printing some small areas, the danger of a jam becomes really serious and happens a lot of time.
Solution: find a way to make the printer keeps a steedy flow rate, and volumetric extrusion so far seems to be the way...? Can you tell me if setting into slicer an extrusion rate of something around 0.6, max autospeed of 80mm/s and volumetric extrusion ON and auto speeds ON, this will make the printer to print at... what speed? and keeping the extrusion rate high even in small areas?
Thanks in advance
Re: Volumetric extrusion
April 20, 2016 07:51AM
If all the widths are the same then all the speeds will also be the same and pressure changes are kept to a minimum - but you still have to slow down for the corners.

Interesting. I've been manually setting line widths to 0.5 mm for my 0.4mm nozzle, and manually setting speeds to the same value (except for bridges and gap fill) because I had slic3r do some weird stuff in the past such as printing infill with lines that were narrower than the nozzle diameter. I get consistently excellent print quality doing this.

I've also found that the more manual control I apply to slic3r, the more reliable it becomes. I haven't had slic3r crash in many months even though others complain about it crashing a lot. Besides manually setting line widths and speeds, I set threads to 1. I haven't noticed any difference in slicing speed, but doing this eliminated most of the crashes I was seeing. The final thing is to set the slicing options first, then load the part on the plater. I found that if I make a lot of option changes quickly and reslicing has to keep restarting, it chokes and crashes, even on my moderately fast quad core machine with 12 GB of RAM.

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
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