Saturday, October 20, 2012

Calibrating the Prusa Mendel and get it to print

I wanted to build a mini sumo, and now I am calibrating a Prusa Mendel 3D printer!

Software installation

The first step is to install the software needed:

Virtual COM port

The 3D printer is connected to the PC using an USB cable. After installing the driver you will get an extra (virtual) COM port through which the printer can be accessed.


Pronterface is the user interface software for controlling the 3D printer. I prefer the precompiled version because it does not require installation of Python.


Sprinter is the firmware for the 3D printer. The software runs on the 3D printer itself. The 3D printer lend to me has the Sanguinololu 1.3a board. At the time of this writing, the software is based on Arduino 0023. So you need to install that specific version if you need to compile this software. Check the Sprinter page if this is still true.


Arduino 0023 is used to compile Sprinter.


ABS requires a functioning heat bed while PLA can be printed on a heat bed at room temperature. Because I do not have a power supply that is able to provide the amount of current needed by the heat bed PCB, PLA is the only option for me. PLA is made from corn and melts around 185 degrees Celsius  ABS is an oil product and is used in 3D printer at a temperature of 220 degrees Celsius.

A new hobbed bolt

When I bring nozzle of the printer to temperature and extrude some PLA, the same thing happens again and again: after some time, the filament stops while the extrusion motor and bolt are still spinning. 

The extruder
Original hobbed bolt

New hobbed bolt made by Coen
The filament is clamped between the notch in the hobbed bolt and a ball-bearing. The filament is extruded by turning the hobbed bolt. It turns out that the teeth of the hobbed bolt are somewhat blunt. Coen, a handy friend makes a new hobbed bolt with some more impressive teeth!

Extruder calibration

After installation of the virtual COM port driver and Pronterface, you can use Pronterface to connect to the printer. Select the correct COM port and hit the Connect button.

Use the extrude button to calibrate the extruder. First remove the hot end from extruder so that the filament can run freely without any obstruction. Mark the filament and hit the extrude button after filling in 100 mm.

Now measure the amount of filament run though the extruder. When it is not exactly 100 mm (+/- 1 mm), you must make a correction in the Sprinter firmware. Open the Sprinter file Configuration.h and search for the lines:

//// Calibration variables
// X, Y, Z, E steps per unit - Metric Prusa Mendel with Wade extruder:
#define _AXIS_STEP_PER_UNIT {80, 80, 3200/1.25, 700}

700 is the value you have to update. With my hobbed bolt a value of 633.6 gave the correct amount of throughput. Compile and upload to the printer. First I got next error message:
avrdude: stk500_getsync(): not in sync: resp=0x00 
avrdude: stk500_disable(): protocol error, expect=0x14, resp=0x51 

I fixed that by lowering the upload speed. To lower the upload speed, open the file C:\Program Files\arduino-0023\hardware\Sanguino\boards.txt and change the line atmega644.upload.speed=57600 to atmega644.upload.speed=38400.

A flat surface to print on

After I got the extrusion speed correct it turned out that the heated bed PCB was not flat. It was somewhat bathtub shaped. With a height difference of three mm. That was fixed with a piece of glass on top of the heated bed. Now try to print a 0.5mm_single_wall_calibration_piece. First result:

Printing directly on the glass surface
The PLA does not stick to the glass surface. The image above speaks for itself.

Print result after adding blue tape to the glass surface
Second try after applying tape the the glass surface. Now it seems that the layers do not stick enough to the layers below.

Print result after blowing air while printing
For the third try, we blew some air on the piece, while printing. The result was that the filament got stuck somewhere in the hot end.

A different head

Every time I try to print something, the filament gets stuck. First the hobbed bolt was the suspect, but that has been fixed. Next suspect is the hot end. As an experiment the hobbed bolt and gears are removed so that the filament can be extruded by hand. At the start it is easy to push the filament down, but after a short while, the filament blocks. Than it is not possible the push the filament down. The friend who also created the hobbed bolt read positive things about the J Head. He ordered one and put it in place. The image below shows the result after printing the single wall calibration piece.

Woohoo: good results with J Head!
Now that the calibration piece is successfully printed we can finally try to print the pencil hinge. That's what started this 3D printing journey.

The pencil hinge that started the 3D printer journey
Again success. Now that we made this 3D print journey to a success and learned a lot about 3D printing, Coen and I want our own 3D printer. Time for printer reproduction!

Printing parts for a 'child' printer

The first child printer (Coen's) begins to take shape

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