Extruder calibration (3 replies)

Hi everyone.
I have almost finished my very first 3D printer.
I have already calibrate precisely E-step based on 10cm lengh extrusion (without hotend).
Recently, i fixed the hotend (nozzle = 0.34mm) to the extruder and begin to extrude some cm of my 3mm PLA filament using manual
control of the Repetier-Host. The result was not perfect; the PLA stops extruding randomly during the test du to filament
slippering on hobbed bolt.
So I reduced the extrusion speed to 40 mm/min and add some spring tension. Now it seem to work better. But it was only a manual
test with a constant and ( i think..) a relatively low speed, so i'm not sure that the extruding procedure will work fine during a real
printing process.

So my first question is, what is the speed value that i must choose to make a reliable manual test. Is 40 mm/min too slow ?.

Second question; I must add springs tension to prevent slippering of the PLA filament during normal condition.
But i figure that too much tension is not a good thing because it does not allow the filament to slip when trouble
occur (like when the Hotend jam for exemple...)
Am I right ?

Thanks in advance