05 - Filament Flow Rates (7/25/14)

Post date: Jul 25, 2014 10:42:45 PM

Some other 3D Printer owners that I know have had some issues getting their hot ends to extrude at rates much above 40 mm/min. Much speculation and discussion ensued and I decided to experiment with flow rates for the hot end that was installed at the time.

It happened to be a .4 diameter J-Head Lite and had red Coex3D currently fed to it.

Firstly, I looked in my Marlin firmware config file to see what the max extruder rate was and found it at 25 mm/s (1500 mm/min).

Next, while the .4mm hot end was heating to 185c I made marks with a sharpie every 10mm above the extruder input.

In Pronterface I set the feed distance to 10 mm and at 40 mm/min, primed it a couple times to get a flow, then after confirming it was on a sharpie mark, removed the primed material from the tip and as quickly as possible did the following extrusion rates in mm/min:

160

320

500

I confirmed it fed the full 10 mm each time (no slippage etc.). Each successive operation resulted in a shorter length but larger diameter extrusion (the pic has the last extrusion closest).

I then used the caliper to measure diameters (didn't bother with length):

flow rate (mm/min) ---> diameter (mm)

20 ---> .4

40 ---> .44

80 ---> .5

160 ---> .6

320 ---> .7

500 ---> .75

The Wikipedia entry on die swell seems a fair introduction to explain the diameter behavior.

I have on occasion, successfully printed at 160 mm/sec (perimeter and fill feed rates) but have not calculated what the filament flow rate is for the width/height etc. settings and I'm actually glad I don't have to, that the software figures it out for me ;) At those speeds I have not seen any problems with the extrusion keeping up. I am grateful for this and am lucky to have a combination of components that are working well together.

I found an interesting post with buried tidbits about the hot end melt zone (basically, larger melt zone means higher flow).

Note: I am not promoting any specific products. Reading through the thread I found some interesting ideas, information and opinions.

There is probably less biased or "more scientific" information somewhere, I simply landed on the above when searching melt zones and flow rates...

All of this combined makes me wonder if flow issues are because of too small of a melt zone, there is also perhaps restriction due to some manufacturing issue like debris, high friction internal surface, undersized hole etc. If answers are found, I will try and update this post with more information.