Extruder Drive Force Measurements

[bertho 6]

Instead of printing I ended up spending too much time to satisfy my curiosity. Here is the result:

http://www.vinland.com/Extruder_Drive_Force.html

Note, the sample spring can be even further compressed than what is shown in the data.

Bertho

[alaris2 1]

awesome work Bertho.

I found a new spring for the one I built and it's running beautifully. It's great to finally be rid of extruder problems, many thanks.

of course you realize the next thing will be to get the extruder running faster so we can print at >100mm/s!

[bertho 6]

Thanks Alaris2,

Yes, the next question is how much force do we need vs. printing speed and materiel & temperature.....

Knowing that, I can then calculate speed and spring force and gear ratio if needed.

Happy printing,

Bertho

[Daid 306]

of course you realize the next thing will be to get the extruder running faster so we can print at >100mm/s!

I've printed at 120mm/s with a stock setup. Does require a good oiled machine and a high temperature.

With Joris machines, with a 0.8mm nozzle, the limiting speed factor is not the extruder drive, but the speed at which it can melt the filament.

[joergen 2]

awesome work Bertho.

I found a new spring for the one I built and it's running beautifully. It's great to finally be rid of extruder problems, many thanks.

of course you realize the next thing will be to get the extruder running faster so we can print at >100mm/s!

We had a long discussion about this on the google group, called "reasonable expectations". I am laying down 0.2mm solid infill layers, 0.5mm nozzle at 200-250mm/s, if I am not mistaken (ABS 250C). skin is usually limited to 80, since defects would show, but the inside doesn't matter so much, as long as it is mechanically stable.

[alaris2 1]

Joergen is correct, and we had a related discussion here.

I'd like to think my machine is good and oiled and the temperature is certainly high. I performed a number of tests with the standard 0.4mm nozzle up to 200mm/s (before Bertho's extruder)

very quick summary was:

at 100mm/s prints come out perfect

at 120mm/s there's occasional misextrusion on perimeters

at 150mm/s misalignments (ie. head positioning problem, backlash?) becomes very apparent, more misextrusion, infill becomes blobby and structurally unstable (switching to grid infill helps a bit)

at 170mm/s I couldn't print anything useful.

(Joergen's results show what you can do with a 0.5mm nozzle)

I wouldn't recommend 120mm/s for something you want to show someone and impress them at how good UM is, but if it's for a 'quick and dirty' then it's fine.

I intend to re-run the tests with Bertho's extruder mods and see if there's any change. I did already notice if I up the E value I can print very successfully at higher speeds but at the cost of overextruding on fine details. I guess it's possible to change E within the gcode however, so that suggests more speed is possible.

there's something to think about Daid? post-process the SF g-code to adjust E on the fly for faster extruding - we'll love you for it

[bertho 6]

Real CNC equipment has a speed adjustment setting up or down in % of the G-Code setting. It also has Tehran % adjustment for the spindle speed.

I have not looked but I think there is at least an option in Marlin to vary the speed. Presumably both adjustments ought to be in Marlin.

This brings back my argument about do not change correct values. If the steps/mm value is correct, do not lie about it to change the the print result. I guess we are back discussing a "Packing" fudge factor.

[rewolff 0]

Bertho, I'd now be interested in the force applied by the extruder to the hot end. Can you figure out a way to measure the force that the bowden exerts on the clamp? e.g. remove the gray plastic bolt from the plastic, and put something else in so that you can measure the force there...

[bertho 6]

That is the required extrusion force that I was referring to above. Maybe using Joergen's and alaris2's numbers as an upper practical printing speed for testing.

I wonder at what printing speed the heater runs out of power? That is another interesting data point.

[Daid 306]

 

I wonder at what printing speed the heater runs out of power? That is another interesting data point.

You should ask Joris. He prints with 0.8mm nozzles, and has tested with a 3.0mm nozzle. That way he reached the heater limits.

[phut 0]

I only did some very quick and dirty math on it but I am guessing the bigger factor is the effect of heat transfer between the heater and the filament.

Theoretically you'd be able to get 0.2 grams a second of ABS out of the extruder by imparting 50W of heat to it constantly, which is like 140mm/s of 3mm filament at a guess.

ED-that sounds wrong actually... I worked from 20m of filament on a 750g roll.