Speed control (especially with larger nozzles) or Volumetric printing

[mpirringer]

Hi.

Some slicers now support the feature of volumetric printing or at least allow you to set a max volumetric parameter. I will discuss the difference and what it does for you and how you can do it manually if your setup does not support it.
Each hotend/nozzle combo has the capability of properly melt the filament at a certain rate. E3D will not post tables as they are different for each filament and each temperature and each nozzle but the info below is based on discussions with them. So for example the hotend will have a different rate to melt PLA at 210 than at 215 and a different brand of PLA might be different and that is all with the same nozzle the value might change again if you go from a .4 to a .6 or .3 Nozzle so to get the value you have to figure it out yourself to do that you have to send some G commands to the printer to extrude some filament.

1.) wait until hotend heats to desired temp and load filament and extrude some to get rid of whatever was in there before.
2.) Type G91 into the terminal so you do not use absolute values

3.) Repeatedly type in G1 E50 Fnnn; (nnn is a speed)

This command will extrude 50mm of filament enough to build up pressure and give you something to look at. nnn is the speed in mm/min so F60 will extrude at a speed of 60mm/min or 1mm/sec.

IF you have 1.75mm filament than the cross section (r2*PI) is 2.4mm2 so each mm of 1.75nn filament is 2.4mm3 of filament so a command
G1 E50 F60;will extrude filament at 2.4 cubicmm per sec.
G1 E50 F300. will exturd 12 mm3/sec

You pick a start value that you consider safe and start going up after each time you inspect the filament extruded. IF it starts to get bulges or balls or you hear the extruder starting to click or after the extruder stops filament still poors out the hotend for a couple of seconds then you are going too fast and go back to a speed that gives good results. Then deduct 10% and lets say your calculated value is 360 then your max volumetric throughput is 360/60/2.4 = 14.4 mm3/sec You enter that in your slicer. Now on a ,4 nozzle it might not matter as your max speed might be the max speed your printer is capable lets say 60mm/sec if you print .4 wide and lets say a layer height of .32 which is the max suggested then each mm you print will have 0.128 mm3 of filament if you print at 60mm/sec then you will extrude 7.68 mm3 of filament which is about half of what you can . So if you go to a .8 nozzle and you have a slicer capable of reducing speed based on max mm3/ sec then it will perform a calculation like that. Assume .96 mm extrusion width and .6mm layer height then each mm extruded will have 0.576 mm3 of filament with our 14.4 mm3/sec max extrusion you will get a max speed of 14.4/0.576 = 25 mm/sec if you drop the layerheight to .3 you can move at 50mm/sec Either print with either layer height due to the different speed will take the same time so now you pick the layer height that is best for other reasons. If you have a layer height too high for the speed then you will get the before observed extrusion problems and a crappy print. Now that explains volumetric max.

Volu,etric printing is done by the firmware where the slicer sends the E(xtruder) values in mm3 insted of mm. How for example marlin seems to work is that when you send a command in mm
G1 Xxxx Ennn Ffff
then that means extrude nnn mm while moving to xxx at speed fff and marlin will divide it out in volumetric the command
G1 Xxxx Ennn Ffff
Is interpreted to extrude nnn m3 over the same distance while moving at speed fff which means you extrude the same amount of filament for each mm or fraction thereof over the distance. this eliminates to a great deal thickening and thinning of walls due to acceleration and deceleration and give more accurate better prints. There are 2 slicers to my knowledge that support that one experimental (cura) and one official (slic3r) In each you have to enter (For marlin)
M200 Dnnn ; S0 or S1 etc if you have multiple extruders otherwise for 1 omit
nnn is the thickness of the filament
so
M200 D1.75 ; Turns volumetric on for 1.75mm filame M200 D0 turns it off
DO NOT enter this unless you are using a slicer that supports volumetric and is set to volumetric mode as there is a huge difference if you extrude 10 mm of filament or 10mm3 of filament as for 1.75 mm filament 10mm3 are about 4.2mm of filament

Bottom line even without any slicer support for volumetric extrusion or volumetric maximums knowing about them you can use them to determine the proper max speed for a particular filament. You probably will not need to if you are only printing PLA with a .4 nozzle or smaller but if you use a larger nozzle and/or get into other filaments especially (semi)flex establishing those limits can make or break a print