what does "Extrusion Multiplier" do?

OK, so from my printer wiki I need to do some calibrations. First I made sure the motor which is pulling the filament in is moving the correct amount of steps per mm by following a guide from their wiki.
In the next page, I'm told also need to make sure the correct amount of plastic "is coming out as well", by printing a 1-layer thick wall, measuring its with with a caliper, then changing the "Extrusion Multitplier" in Slic3r by doing some calculation with that data.

I dont get it, what's the point?
Isn't changing the "extrusion multiplier" just talking the "Steps per mm" number which I've already calculated and entered in my software and multiplying it with the "Extrusion Multiplier" number from Slic3r settings and using the resulted number instead? Because if it is, then shouldn't there be no need for multiplying the number I've already calculated and I should just set the multiplier to 1?
What am I missing?

Yes, extrusion multiplier is to fudge the numbers a bit when the machine is not perfectly calibrated. larger number equals more plastic being extruded. It can be used + or - and can be minute amounts like 1.05 or .95. If the machines is perfectly calibrated then it should be set at 1.

Thanks. That's what I thought.
The Solidoodle wiki said "Once you get your extruder calibrated, you know that the right amount of plastic is going in, but you still need to make sure that the right amount of plastic is coming out.". Unless there's clogging, I dont see why I need to do that.

Edited 1 time(s). Last edit at 10/05/2014 03:48AM by anon92.

Quote
anon92
OK, so from my printer wiki I need to do some calibrations. First I made sure the motor which is pulling the filament in is moving the correct amount of steps per mm by following a guide from their wiki.
In the next page, I'm told also need to make sure the correct amount of plastic "is coming out as well", by printing a 1-layer thick wall, measuring its with with a caliper, then changing the "Extrusion Multitplier" in Slic3r by doing some calculation with that data.

I dont get it, what's the point?
Isn't changing the "extrusion multiplier" just talking the "Steps per mm" number which I've already calculated and entered in my software and multiplying it with the "Extrusion Multiplier" number from Slic3r settings and using the resulted number instead? Because if it is, then shouldn't there be no need for multiplying the number I've already calculated and I should just set the multiplier to 1?
What am I missing?

It's because there is no perfect world when it comes to extruder calibration. You may set it perfectly at 100mm for example but that doesn't necessarily mean you will have the perfect extruded amount when it comes to printing. The idea of the single walled print is to allow you to measure the wall thickness and adjust if needs be - the multiplier is a fine adjustment. You may of course have the perfect measurement right off without any multiplier involvement so your number would be 1.
Have you printed a single wall box and measured it?

---

_______________________________________
Waitaki 3D Printer

You will find that different filaments often need different multiplier factors to give the same result. I'm not entirely sure why that is - my immediate thought was that the filaments are slightly different diameters, but measuring them seems to show that they are accurate. Maybe some filaments shrink or have small air bubbles causing the extruded volume to be less than expected.

Dave

Think also about this. The filament could be of a softer or tougher material. This may even vary by pigment used to color the same basic material, not to mention different materials (e.g. ABS vs. PLA).
Now, even if they have the same diameter, when the hobbed or knurled bolt is driving the filament, depending on the extruder type, the teeth will "bite" differently so that the length of the filament that will be extruded for the same length given by the Gcode will differ.