So, I have a question about direct drive extruders.
How is the gap between the feeder gears adjusted to accommodate new filament and/or filaments with different diameters? Particularly on printers like the Bambu Lab that can automatically swap it out, since obviously you can’t manually pinch the spring clamp like you can on Bowden extruder printers like the Ender 3.
I’m working on a design project where I need to come up with my own direct drive system so I’m curious to know how the filament swapping is managed while still keeping the proper pressure of the gears against the plastic.
Most high quality filament you will find nowadays is pretty standard at 1.75mm, usually these don’t vary all too much so we don’t really have to worry about variable spring tensions. Generally once you have tuned your spring tension in properly you can apply that to basically everything successfully.
The way that the Bambu machines handle filament swapping is that the springs in their extruder are set up to be the correct tightness from the factory. Then they can cut the filament inside the nozzle and retract it using the extruder, the cutting ensures there is no stringing and that the filament will extrude properly on the next attempt. Once the filament has been fully cleared from the extruder it is then grabbed by a servo in the AMS which retracts it back onto the spool. Then a new color is sent out.
But ultimately, as long as you are using decent quality filament and have your spring tension dialed in properly you won’t need to worry about variable spring tension.
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As far as I know all direct drive use a tension system, a spring usually. Once the correct tension is set it rarely (never?) needs an adjustment. Because they use a feed command and the rollers are powered they grab the filament.
Most others the filament is pushed not pulled and it needs help to start. Hence the need of an arm or something.
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