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Extruder steps per mm!

Posted by homecore 
Extruder steps per mm!
July 23, 2012 10:17AM
Hi guys,

I'd like to start a topic in which we can all verify our calculated E_steps_per_mm values. For the new people (me up until yesterday): this is the number of steps your extruder stepper motor must get to pull/push 1mm of filament through the extruder. The formula to calculate it depends on the mechanical construction of your extruder of course. Let's all explain it for our own extruder and verify?

I have a regular Adrian's geared extruder, with following specs:

Nema17 motor with 1,8° per step
Gen6 electronics  = 1/8 microstepping is used > it thus needs 8 microsteps for a revolution of a full 1,8° step
pinch wheel diameter 7mm (Mendel-parts Brass insert)
59/11 gear ratio. (ratio of the driven gear vs. the drive gear of your extruder stepper motor)

E_steps_per_mm = 360/1,8° * 8 * 59/11 * 1/(Pi*7) = 390,2397 theoretical steps per mm

correct? thank you!
Re: Extruder steps per mm!
July 23, 2012 11:34AM
I have a toothed, not hobbed, bolt in a Wade's/Greg's extruder, a 200 steps/r motor, 16x microstepping and 33/13 gear ratio.

E_steps_per_mm = 200 * 16 * 33/11 * 1/(Pi*7.5) = 407.4 theoretical steps per mm.

I'm using 420 right now and the extrusion is quite accurate.
Re: Extruder steps per mm!
July 24, 2012 01:51AM
Many people recommend the try-and-error approach. With a hobbed bolt, for example, it's difficult to measure the effective diameter. So, unmount the hotend, set STEPS_PER_MM to 100 and measure how much the filament is forwarded. Adjust STEPS_PER_MM and iterate 2 or 3 loops, just like the other axes.

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