Relation between extruder speed and moving speed
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Hi,
What is the relationship between travel speed and extrusion speed? I want to find out... How fast you can print, I guess it will depend on layer height and material. What else? What relationship exists
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@peirof the maximum travel speed depends on the mechanics that move the print head (and bed, if applicable). The maximum printing speed is typically limited by the maximum speed that your hot end can extrude plastic at, which depends on many factors including heater power, melt zone length, nozzle size, and the power of the extruder drive. There are specialist hot ends for high flow rate extrusion from all the major hot end manufacturers.
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To calculate extrusion speeds, plug your numbers into the formulae for volume of a cylinder (filament) and volume of a rectangular prism (extrusion).
When the approximate volume for both is equal, you now know your linear speed for E (it's the height of the cylinder).
E.g.:
0.2 mm layer height
0.4 mm extrusion width
1.75 mm diameter filament
100 mm/s print speed (X/Y)Rectangular prism:
V=whl=0.4·0.2·100≈8Cylinder:
V=πr^2h=π·0.88^2·3.32≈7.98554So the height of the cylinder (3.32 mm) is approximately the speed in mm/s that the E axis will have to move for the given 100 mm/s 0.2x0.4 extrusion parameters.
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I've been thin king about a method for finding the fastest extrusion speed for a given extruder/hotend. I think the process would be something along the lines of extruding in space (not making a part) and increasing extrusion speed until the hot end heater cannot maintain the temperature. Then you could use bots formula to calculate the print speed for a given layer thickness and line width. You'd probably need to do this for different filaments because the heat required to melt them varies (not sure by how much).
One thing that may affect the experiment is that the firmware may limit speeds (extruder and movement) if the hot end temperature cannot be maintained.
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@mikeabuilder See here for finding the max extrusion rate: https://duet3d.dozuki.com/Guide/Ender+3+Pro+and+Duet+Maestro+Guide+Part+4:+Calibration/40#s177
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@mikeabuilder As someone who has done a lot of work on high extrusion flow rate hot ends, I can say that it's not as simple as looking for a drop in hot end temperature. The reason is that it takes a finite amount of time to melt the filament so the extrusion rate will drop well before there is any change in the temperature of the metal surrounding the filament. The best method I have found is to extrude into air but lower the extruder motor current to a point where the extruder will skip before it starts to grind and strip the filament. At least that works well for me with my Bondtech BMGs. I.e rather than trying to overcome the resistance to flow, use it as the indicator that the maximum volume flow rate has been attained
Even then, it's not straightforward when one gets up into the realms of 100mm^3/sec using large nozzles like 1.5 mm diameter because while the outer skin of the filament will be molten, the inner core might be semi molten or even solid but will still extrude (with strange results). -
@Phaedrux - Thanks for the pointer to that page. Excellent method for finding the max extrusion rate, plus some other gems. I hope that page is making it through the documentation migration. And @deckingman, thanks to you too, for the same basic method. I like using the extruder motor as a measure of "extrudability".
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@mikeabuilder said in Relation between extruder speed and moving speed:
I hope that page is making it through the documentation migration.
It should be but I think it's currently missing. It needs to be reworked a bit and expanded and probably should be its own guide.
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Thanks to all..
You have given me a lot of information, which will take me a while to "digest". Being all useful, you find the guide you have posted @Phaedrux, especially useful. Since it offers a method to calculate the extrusion speed
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@mikeabuilder said in Relation between extruder speed and moving speed:
I hope that page is making it through the documentation migration.
It's planned! Just needs to be migrated, updated, new images, etc. Just got a couple of other guides to do first.
Ian
