Echovoice RepRap - Calibration
Part Five
Now that the machine is done we need to calibrate and configure it. In order to configure the machine we need to use the same program we used in the previous step, electronics. The reason the machine needs to be "calibrated" is to ensure that the g-code sent to the machine is inturpeted correctly. For example when the g-code sent to the machine tells the x-axis to move 100mm the x-axis needs to move exactually 100mm. This will ensure that your prints end up printing exactually how they were designed.
The first step is to get your machine to properly home itself. This is done by adjusting the opto flags so that when the machine is told to "home" itself each axis goes to its apprpriate home location, this is important becuase the machine needs to know where to print objects compared to its home location, ensuring they are printed properly and acuratly.
For the x axis the extruder carriage needs to move
First we need to pull up the firmware again and go through the configuration files. Go ahead and pull up the 5D firmware in the arduino software. This is the firmware we used to program our motherboard. In the code go ahead and do a search for "XYZ parameters of Mendel" Here you will find the following 3 important lines:
#define X_STEPS_PER_MM 10.047
#define X_STEPS_PER_MM 10.047
#define Z_STEPS_PER_MM 833.398
The above lines are the default values in the firmware. These values actually worked fine for me and produced accurate resaults. You might have to adjust them, but here is how we can easily test them. You need to send g-codes to the machine telling each axis to move a particular amount. We are going to place a piece of paper
and attach a pen to the extruder.
In order to calibrate the number of steps to extrude 1mm of filement, we need to do some calulations on the nozzel, drive gear, gear ratio and stepper.
From the above pictures you can see how the inside of the extruder works. When the large gear spins, it drives the drive gear pushing the filiment down into the heater barrel and nozzel. Our first step to calculate the number of degrees this has to spin to drive 1mm out the nozzel is we need to calculate how much of our filiment has to enter the top of the nozzel. This math is quite simple and should be too hard for any of you.
So looking above it is easy to calculate just how much feedstock has to be extruded in order to extrude 1mm out of the nozzel. Next I had to calculate the drive gears radius in order to translate the amount of feedstock to drive as an angle.
