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Quick Question Flow changed with speed ?

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A little background on speed. The speed is called the "feed rate" which is not a 3d printing term but a generic CNC gcode term. The feedrate gcode is controlled with the letter "F". The limiting speed on the UM is mostly X and Y. Most moves do not include a Z component. So on normal extruding moves (not bottom layer, not limited by minimum layer time), the feedrate is set to whatever mm/sec you set in Cura. Once set, Cura doesn't mention feedrate in the gcode until it changes. When you do a Z move, the feedrate is specified because 100mm/sec in Z is too fast (on the UM1 anyway) and if you do extrude-only moves such as retraction, the feedrate is specified (but not ulti gcode mode) also because 100mm/sec in E axis (extruder) is much too fast.

Now on the controller for UM1 and UM2, if you change the "speed" you are multiplying by a percentage. So by default is 100%. If your feedrate in Cura was say 60mm/sec then speed=100 is 60mm/sec.

If you increase feedrate to 200% you will be printing at 120mm/sec. 10% will be 6mm/sec.

If your non extruding moves were 150mm/sec and feedrate is 200% then the non-extruding moves will be at 300mm/sec.


There is a max speed and max acceleration for all 4 axes. For example, typical XY max speed is 300mm/sec. If setting "speed" or FR (feedrate) to 200% goes over these max values then it will only increase up to the max speed. Changing the FR to 200% does not affect the max speeds or the accelerations. So printing at 200% will never print twice as fast. If you were printing slow enough then it will be almost twice as fast but never quite.

Also Marlin continues to be very careful to never violate jerk or acceleration settings and always move in a straight line (linearly). So if the extruder only needs to move 1mm and the X axis is moving 200mm, the limiting speed for the extruder will be set by the acceleration, max speed, etc of the X axis.

Changing flow in effect changes the steps/mm of the extruder (without violating the existing max speed of the extruder).

Basically Marlin implements all this just the way one would want it to work.


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Also be aware that if you set your speed over 100% and some of the layers hit the "5 sec minimum layer time" or whatever your layer time is, then you will be overriding this minimum layer time. For example if you had it set for 5 seconds and you print at 200% then the quickest layers will be printed closer to 2.5 seconds and they might not have time to cool before the next layer is printed.


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It depends on the printer. For UMO I think you just rotate the control from the main menu. On UM2 and UM3 you go into the tune menu. There should be a setting called feedrate or speed. Something like that. It defaults to 100 (100%). Change it to e.g. 50 and you'll hear the printer slow down to half speed. You can go up to I think 500%. But this is the *goal* speed. If the line segments are very short it might not be able to reach the goal speed. Also printers have a max speed. For UM machines that is 300mm/sec.

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