Spring pressure vs flow rate

I was calibrating the flow rate on my R2 and I discovered that the flow rate was directly proportional to the extruder temperature. I put in my adjustable spring pressure arm and began with the spring pressure very high. I found that I needed this high pressure to give me a knee at the lowest temperature I would use on this filament. I could now calibrate flow rate independently of extruder temperature above the knee.

This is important because if I am operating spring pressure in the linear range of flow vs extruder temp the PID will oscillate the temp about 1/2 a degree in a pretty constant frequency. This can generate moire patterns visible macroscopically whose visibility is dependent on the ratio of print line length to oscillation frequency. Removing the modulation of extruder temp on flow rate will improve the finish.

I repeated this on my Hypercube variant and it was quickly obvious that my Hypercube variant runs 10C hotter than my R2.

From now on I will check the flow rate of any new filament to find out if the knee is below my operating temperature range, adjusting the spring pressure to the minimum for the task.

 

To set up this test I use Octoprint. I removed the Octoprint upgrade plugin because you can not set extruder temp with it. That reverted me to the "old" Octoprint which works well. I did that over a year ago an do not remember what I did ( I followed Jerry's instructions ).

I use Octoprint "Temperature" to set the extruder temp. I use a piece of tape and mark off 120mm on the filament. I then use Octoprint "Control" and extrude 100mm. I measure the remaining filament, which should be 20mm. If I measure 23mm it means I only extruded 97mm of filament.

I do this every 10C for the temperature range of the filament and verify that the knee in the curve is at least 10C below where I will run the filament.