Extrusion speed vs extrusion error

Hello!

Behold my experimental data

CONDITIONS:
White PLA (local cheap brand) 1,75mm, 0.6mm nozzle, 200C temperature, nozzle is 50mm from the bed.
MK8 extruder (direct, not geared, not belted, approx 100 steps/mm)

I extrude some length and some feedrate and then weight on a very precise scales (0.01g)

Extru   feed    extusion  weight (g)
sion    rate    diameter
length          (mm)
				
200	60	0,69	0,58	
200	360	1,13	0,54	
200	360	1,13	0,55	 one skip
200	300	1,01	0,56	
200	300	1,01	0,54	
200	240	0,93	0,54	
200	180	0,76	0,58	
				
200	300	1,02	0,54

The last line is the result where i tried to help pushing the filament into extruder to exclude problems with filament unwinding force.

Tried at 300mm/min at 220C
weight 0.57g
d 0.95mm

Then i thought maybe i need to increase the extruder tention.


Increase tention:
200 С, 200mm, 300mm/мин
weight 0.54
Very tight
weight 0.50 - a lot of skips
Release a little
weight 0,55

Control extrusion at 120mm/min

0,58g

230C at 300mm/min

0,58


Now, let's calculate maximum speed with correct feedrate.
For 200C maximum feedrate with no error is 180mm/min.
For simplicity let's consider layers have rectangular section.
Layer 0.2mm. Extrusion width 0.76. Which seems like a natural width for this temperature. This is a totally separate question, haven't thought about it yet.
Section area is 0.2x 0.76=0,152 mm2
Max speed 180mm/min=3mm/sec
Filament area is 2,4 mm2
So, at speed of 3mm/sec we can extrude 2,4*3=7,2 mm3
7.2 mm3 / 0,152 mm2 = 47mm/sec

This is maximum print speed for the given condition.

I cannot say anything about 0.4mm nozzle, because it needs to be tested at all speeds to get data.

Now, let's say we print the same 0.6 nozzle and same conditions but 0.1 layer, the speed can be doubled.
But if we print 0.4mm layer then speed must be halved to get correct extrusion.

Well, apparently we can use hight speed to internal structure and then use correct speed for the external layers and shells.

Edited 2 time(s). Last edit at 03/01/2018 05:49AM by ArtemKuchin.

You don't have enough data points to determine the extent of the reduction of extrusion amount (i.e. weight) with feed rate accurately; however it looks like you are getting a reduction in extrusion weight from 0.58g at low speeds to 0.54g at high speeds before the extruder starts skipping steps. That's around 8%, which is similar to what others have found.

RepRapFirmware has a nonlinear extrusion feature controlled by M592 to compensate for this effect.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

How luck for RepRapFirmware users
Unfortunatelly i use Marlin which does not have such feature as of now.
Slicers do not have feature too.
So, is such situation for better quality i am stuck al low speed or at least low speed for external shells and layers.

Good to know that it was found before and i am not crazy

Quote

Slicers do not have feature too.

They do, it's called extrusion multiplier (EM). Say you want to print with 47mm/s, then use EM=1. You want to print at 94mm/s, then use EM=1.08

Will not work. Every feature has different speed, first layer, outer shell, infill, bridges. Cannot set extrusion multiplier for each. Also, it is not linear at all to set one number.

Edited 1 time(s). Last edit at 03/01/2018 03:10AM by ArtemKuchin.