Retract update…
Someone mentioned using 40mm/s for retract, which was counter to ohter folks listing 150 to 200 mm/s. The faster retract rates were noisy and didn’t seem to help, I’m homing in on a good ballpark, but Cura’s recommended 4.5mm retract at 40mm/s sure seems ‘proper’.
Just saying, if you’re having problems with retract, try a little slower, too.
It’s possible to be more specific than that.
Some extruders, such as direct drive extruders can retract much faster. Accessible extruders are geared down which gives better precision but significantly reduces speed. Material also matters. PLA can put more resistance on an extruder than ABS. Different hotends can provide different leeks of resistance as well.
Faster is better but as you have found, it is important not to retract faster than the extruder allows.
It’s making me think that the really high retract rates caused slipping of filament or lost steps, which may have contributed to the starvation issues I was having.
Further thinking, is there a difference between direct drive and gear reduction, even if they’re calibrated to move the same amount of filament? I’m thinking acceleration would be different and that 40mm/s on a gear reduction extruder WOULD be 100mm or so on a direct drive?
As mentioned, the speeds that you can go depends on gearing (actually on steps/mm, and on how much excess torque you have, and the torque/speed curve, and friction, etc.). You want to retract as fast as possible, but you want to recover from retraction at a slower speed, both because there will be more forces acting against you (thus more torque is required and the maximum speed is lower), and because you want to repressurize the nozzle at a speed closer to your printing extrusion speed so that it is equalized when you start printing again.