Static extrusion speed vs printing speed

[Lee]

Strange question but if I print a line 100mm long through a 0.4mm nozzle @ 80mm/s linear speed. What speed is my extruder spinning at? 3mm/s?

[tray]

It's a constant volume problem, so cross section of the stock filament time the feed speed equals the cross section of the output times the nozzle speed. ( Nozzle size doesn't directly matter here.)  

[Rich Webb]

Engage swag engine!

Since volume in must equal volume out, the ratio of in to out should be the ratio of the cross sectional areas (assuming sufficient hand-waving). Since you're printing a line and not extruding a noodle, the exit cross section would be 0.4 * 0.2 = 0.08 mm^2 (vice 0.126 mm^2 for a circular cross section and assuming a rectangular extrusion of 0.2 mm layer height). The feedstock is 1.75 mm, so 2.4 mm^2. The ratio of gozin to gozout would then be 0.033 and an 80 mm/sec extrusion would require a 2.7 mm/sec feed rate. To figure out how fast the stepper needs to turn, you need to know the diameter of the feed gear. Mine is about 10.7 mm so that's 33.6 mm/rev. So, ((2.7 mm/sec) / (33.6 mm/rev)) * (60 sec/min) = 4.8 RPM.

On Thursday, December 27, 2018 at 5:39:25 AM UTC-5, Lee wrote:

[Lee]

Thanks guys. Didn't understand a word but I have the answer I was looking for :)

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