Extruder Calibration

This tutorial shows you a simple method of how to calibrate a 3D printer Plastic filament extruder -

Extruder Calibration - 

And as with every other 3D tool-path generator you need to have a calibrated extruder first before you can get awesome looking prints. it’s really easy to do and will save you so much messing about when you attempt to compensate for poor calibration.

So you will need to set the correct steps per mm of used filament in the firmware, you can work this out by just extruding some plastic, I recommend using Printrun (Pronterface) Get it here

To do this you will need to edit, re-compile and upload firmware to your electronics, I’m going to assume you already know how to do that using the Arduino software. – (If not let me know).

So in most firmwares like Sprinter or Marlin you will find lines in the Configuration.h file that look like this -

//// Calibration variables

// X, Y, Z, E steps per unit – Metric Prusa Mendel with Wade extruder:

float axis_steps_per_unit[] = {80, 80, 3200/1.25,700};

The number at the end (700) is the number of motor steps needed to extrude 1mm of the input feedstock plastic.

Your number could already be different and may be half of this if you are using 8x microstepping (GEN6) instead of x16 (RAMPS usually uses x16).

Every hobbed bolt and filament drive / extruder gear setup is slightly different, so it’s a very good idea to calibrate.

Now we need to check if this number is correct for your filament drive and the plastic you are using, you can use Pronterface  to extrude an exact amount of filament and we are going to measure the distance to check if it’s correct or not -

First check that your filament drive (Hobbed bolt) is clean and free from any plastic or debris.
Feed the filament in and make sure your hot-end is at temperature.
Make sure your Extruder gears are really meshing well and there is no wobble, move your motor so you have no extra play.
Set your spring compression, this does make a difference as the hobbed bolt teeth dig into the filament -
For 3mm PLA I have the springs quite tight with only a small amount of compression remaining.
For 3mm ABS I slacken them off just a little more.
For 1.75mm filament, I find you need less compression.
Then stick some tape or make a mark on your plastic filament about 50mm up from the extruder, somewhere you can measure as accurately as possible (try to use a digital gauge if possible)
Either measure this or set your digital gauge to zero measured out to this point.
Tape makes it easy to align the edge to the digital gauge.

 

Now you can extrude 30mm of plastic. You need to make sure you don’t do this too fast as you do not want your motor to skip steps or the filament drive getting jammed.
So either slow down the speed to about 50mm/min and enter 30mm and hit Extrude or I tend to extrude 5mm at a time with a little pause in-between until 30mm has been extruded.
Now check how far the filament marker has moved with your digital gauge -
it should have moved around 30mm if your firmware is close to the correct number.
If it’s exactly 30mm, then you already have a perfectly calibrated extruder :)
If  not then this is how to set the new number in firmware-
Our firmware in this test was set to 700 steps per mm and we extruded 30mm of plastic.
700 x 30 = 21000 (E motor steps for 30mm)
 For example if you actually measured 32.6mm then  21000/32.6 = 644 (so you need to put 644 into your firmware replacing the 700 we had before, re-compile and download and you can re-check again and your filament should now move exactly 30mm as you have just calibrated it.
If you measured 27.2mm then 21000/27.2 = 772 (put 772 into your firmware)

I recommend that you do this calibration for both PLA and ABS (the hobbed bolt teeth can sink deeper into ABS filament, so you will usually have a different Estep value for ABS) and if you have 3mm and 1.75mm extruders then check them also.

You can always add all your calibration readings into the firmware and comment them out so it’s easy to change if you change plastic type or extruder.

Now you have a perfectly calibrated extruder, you are well on the way to perfect printing -

 

This method was first posted up on my Blogger blog (Slicer is Nicer Part1) 6th Jan 2012

 

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