Extrusion Speed vs. Print Speed

[jmunkki]

Hi,

In Simplify3D you control print speed as mm/minute and in Cura, it's mm/s, so there's a 1:60 difference there. In Cura, if I set the speed too high, it will warn me that I'm trying to push too much plastic through the nozzle, which seems pretty smart.

I guess the relationship between print quality and speed comes from at least two factors:

- Mechanical accuracy of the printer movements at high speed.
- The ability of the hot end/extruder to melt and output enough filament to fill the required volume.

For this post, I'm just interested in the extrusion volume speed.

If the nozzle width is a constant and we assume that the path is always the width of the nozzle width, then the extrusion volume needed to fill the path depends on the length of the trace and the height of the slice. The length of the trace per time is what you can control in Simplify3D and Cura as the print speed, but it seems this completely ignores the layer height (except maybe in the warnings that you get from Cura).

So if I'm printing 0.2mm layers on my Wanhao i3 at a maximum of 2600 mm/minute with good results, I should be able to print at higher speed when using 0.1mm layers. In fact, the Simplify3D default for my printer is 3600 mm/minute.

Let's make this a feature request:

Instead of controlling extrusion speed with just distance/time, add an extrusion volume limit number as well and cap the extrusion speed to the slower speed of these two. I might then leave the extrusion distance/time setting at 3600 mm/minute and set the extrusion volume setting to 0.4 mm (nozzle width) * 0.2 mm (layer height that works well at 2600 mm/minute) * 2600 mm/minute = 208 mm^3/minute (we could add a pi to the formula to make it more accurate, but the point is to include layer height in the calculation). So using 0.2mm layers, I would get a 2600mm/minute extrusion speed (plus modifiers for skin & infill etc). And at 0.1mm, the 3600 mm/minute limit would have kicked in because the volume extrusion limit would have allowed 5200 mm/s.

I guess the bottom line is that I think that layer height and extrusion speed should be connected somehow because the printer is extruding volume and not flat surfaces. The Wanhao i3 is in my opinion a very good printer that is restricted in speed by the ability of the PTFE-lined hot end to melt plastic.

If the hot end can not melt enough plastic, I suppose you end up with more pressure from the filament feeder, which could interfere with retraction settings as well -> you should end up with stringing when the excess filament has a chance to ooze through the struggling hot end?

[CompoundCarl]

You can use mm/s in S3D if you want. Just go to Tools > Options and make the change.

And you can also easily adjust the printing speed for different quality levels. You just need to add the appropriate settings into the <autoConfigureQuality> sections (this has been explained MANY times on the forum, so if you think it would be helpful then you can search for it)

[danielhenley]

From what I understand the limiting factor of speed isn't how quickly plastic can be pushed through the nozzle it's how quickly the nozzle can be moved by the steppers without causing problems due to inertia.

[tenaja]

From what I understand the limiting factor of speed isn't how quickly plastic can be pushed through the nozzle it's how quickly the nozzle can be moved by the steppers without causing problems due to inertia.

That is going to depend entirely on the machine.

[danielhenley]

From what I understand the limiting factor of speed isn't how quickly plastic can be pushed through the nozzle it's how quickly the nozzle can be moved by the steppers without causing problems due to inertia.

That is going to depend entirely on the machine.

It will vary with each machine, but is there such thing as a FDM printer that has a head so light that it isn't the limiting factor when it comes to speed?

[tenaja]

It will vary with each machine, but is there such thing as a FDM printer that has a head so light that it isn't the limiting factor when it comes to speed?

Just today I experienced printing with MadeSolid PET+, and my machine could not feed the material as fast as it could move the printhead. The heater could not keep up while running at full speed, a blistering 25mm/sec.

[Brunibbels]

+1 for the Thread.
I would as well have a cap for extrusion volume / s
Of course we could just calculate the flow according to speed. But a real software cap would be easier.

Reasons:

1) Your material is heated up within your chamber. If you go to some extrusion-limit you would need to increase temp to have the material heated up well. Ok, for that you might just buy some Vulcano.
2) With more force needed to push in filament into your hotends "slip" might increase and therefor you decrease the weight of your parts.
Slip is not a big matter of hard material but if you are gonna print softer material it can cause -35% less material.
3) If you are using very thin nozzles extrusion per second is your limiting factor. It depends on your nozzles quality and shape. It also depends on your nozzles output-hole length.

To actually get some feeling on the extrusion-max we would need to cap it and set speed unlimited.
I guess some printers would then cap speed according to their settings.

(Why do I have this intel? I print with force sensors inbetween extruder and nozzle since over a year and got some other feeling for the problems printers have.)