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Hi,

Can somebody tell me what the normal feedrate for the extruder would be for a Kossel Mini ?
Extruder is missing steps.

Gr.
Christoph

It depends. There probably aren't a whole lot here who own Mini Kossels, but it will depend on the motors, hot end, Bowden length and routing, material, and temperature, among other things.

If it's genuinely skipping steps before it grinds the filament, you probably have too much or too little current going to the extruder drive motor. I recollect the guideline being around 80% of rated current or you can decide which way to change it by seeing if it's getting excessively hot.

I've been meaning to make a youtube video about this. I'll post it here, if I ever get around to it.

I have several mini kossels. But "normal feedrate" depends on so many factors. The primary one is hot end and extruder - what do you have? Next would be nozzle orifice size, slicing parameters like layer height and extrusion width, print speed in mm/s and the filament type and temperature.

Basically, the root of the question you are asking is what is the maximum flow rate in mm^3/s for your hot end. That will be the limiting factor for overall print speed in most cases. The E3D V6 is around 8-10mm^3/s. The reason E3D came out with the volcano was to increase the flow rate significantly to over 20mm^3/s. Once you know your system's max extruder flowrate you can back calculate your max print speed:

(max extruder flowrate mm^3/s) / ( layer height mm * extrusion width mm) = max print feedrate mm/s

So let's assume you have a V6 and are printing PLA at reasonable temperatures. Let's use the conservative 8mm^3/s flowrate for the V6 and .2mm layer height and a .4mm diameter extrusion width (nozzle size):

(8 mm^3/s) / (.2mm * .4mm) = 100mm/s

This is the absolute maximum speed you should expect to print and many other factors will reduce this. A good rule of thumb is to use 80% of that and creep up until you have problems. Then you'll know your max for that model, slicing parameters and filament. Even factors like retract will introduce big variations so infills that require a lot or retract or a lot of very small model features will lower your actual max print feedrate.