# Arcol blogJust another RepRap weblog

13Jan/10Off

## Machine Calibrating

In this blog post we try to answer the question, what should be the layer height if the head speed is 16mm/s and the motor speed is 40rpm. So calibrating the extruder theoretically, rather than trial and error.

Since I had my printing machine I always had some sort of printing deficiency. I always suspected,

I asked on the forum how am I supposed to set my machine/skeinforge settings right, and I was told that I should follow this walkthrough blog post.
I tried it, but I lacked the proper tool to do it right. I only have an "analogue" caliper, where the accuracy in theory 0.05mm, but Im only able to read it reliably 0.1mm:

Following the above tutorial requires a digital caliper with 1 µm (0.001mm) measuring accuracy.

The idea, that a measuring is required, when we know every details of the machine, is rather strange. So I asked nophead, what is his method to adjust the settings right. He said, he calculates the layer height and does not need to do any "trial and error", like the above mentioned blog post. We exchanged some emails, and here it goes the explication (at least what I grok from it):

So we are trying to determine the layer height. Before we start, I think I should clear up the terminology and the known/unknown variables.

Terminology:
Known values:
Unknown values:

Calculating the output diameter

Assumption: What is going into the extruder is coming out too.*

So the input volume is equal to the extruded volume:

*: Ignoring the thermal expansion.

The volume of a cylinder:

So:

The cross-section of the input filament and the output filament is a circle (the deposited output filament has an oval shape, but when it comes out from the extruder nozzle, it is round).

So the input and output Volume is:

We know, that , so:

After much simplification:

Where and respectively.
So:

We can simplify with T:

Where . And is:

Where :

And :

is and is .

So finally the equation:

From this:

Hope it was useful.

• The nozzle size does not come into the equation.
• it sets practical limits on . Must be less than the die swell
• The depends on the plastic and the

Note: Also I didnt tried out in practice. So I will update the post once I tried it out.
Note 2: The Mendel building is progressed quite well, just Im a bit behind with blogging.