3d printing firmware extruder help

[3dkarma]

So if i do E20 it will put 20mm of filament in the extruder?

Yes.

And if it has done that it stops?

Yes.

But what speed does it do that?

Whatever your extruder steps per mm is set at. You set the steps per mm, tell it to extrude a certain number of mm and it will take that, the steps per mm, work out the number of steps needed to extrude the specified mm length and turn the stepper motor that number of steps. The printer firmware works out the speed it needs to do the extrusion based on the length of the trail that needs to be laid down and the speed at which it needs to be laid down.

Can i just leave that E paramenter ignored and just poop out fillament at the begin of a move and stop with that at the end of the move?

No. Think about what the printer is doing - there is a relationship between how much filament is extruded, the length of the extrusion that needs to be laid down and the speed the print head moves while it's being laid down.