Tuesday, October 11, 2011

Prusa Mendel RepRap: Calibration Part Three

In Calibration Part Two I offered an entrée into RepRap firmware, and I know you're probably excited to start printing. Good news, that's what happens next. The thing that's needed now is the program that slices the model into layers and writes the program for movements of the extruder head. The program for that is called Skeinforge.

Skeinforge can be used as a stand-alone program, but also as a plug-in for pronterface.py. With it, you can load a file that has not already been sliced and diced into gcode, the step-by-step instructions sent to the printer. Normally you load the gcode file directly into the printer host, which in this case is pronterface.py.

If you haven't already, download Skeinforge and extract the folder into the printrun folder. The thing you need to do to get Skeinforge working as a plug-in for pronterface.py is simply ensure that there is a folder called skeinforge containing all the Skeinforge files in the same folder as pronterface.py.

You can open the stand-alone application by navigating to printrun/skeinforge/skeinforge_application and running the file skeinforge.py. Like pronterface.py, Skeinforge is a Python script, so you may need to take steps to permit the program to run, and of course you will need to have Python and associated dependencies installed and operational. Run the program once and a hidden folder will be created in your home folder called .skeinforge (as in, dot skeinforge). This is where the printer profiles are kept.

To get printing quickly, you can download and install a profile that Spencer Renosis maintains as a service to beginners. He's quite proficient at creating profiles that provide a great starting place for printers. He has instructions for how to use the download, but essentially the process is to replace the .skeinfoge folder on your computer with the one he provides. A word of caution, as of this writing his profiles are a little behind the current release of Skeinforge. Profiles for different versions of Skeinforge are incompatible. If it looks like his profiles have not been updated to the most recent version of Skeinforge, the package of files usually contains the version of sprinter and Skeinforge he is currently using on his printers. You can change over to those for the time being.

Open Skeinforge again and select the most recent stable profile for Extrusion,  which has the date of the profile and the version of Skeinforge used to create it in the name. The README file has specific information about the name of the profile. Close Skeinforge.

Now it's time to print! Open pronterface and load a file. I wanted to start with something fun, so I downloaded the Movember Ring from Thingiverse.com. On that page of Thingiverse you can see two files at the bottom of the page ready for download. One is the SCAD file and the other is the STL. SCAD is a file format of OpenSCAD, a 3D modeling program and the top of the 3D printing toolchain: 3d modeling program (OpenSCAD) > stl > gcode (skeinforge) > printhost (pronterface) > firmware (sprinter) > printer.

The STL file is the intermediate format of a 3D model, and it's ready for slicing in Skeinforge. The STL file doesn't represent any particular software, it's just a kind of model format. STL is to 3D modeling what a JPEG is to Photoshop.

Download that STL file and select it as the file you load into pronterface.py. You will see messages in the pronterface monitor pane showing the progress of Skeinforge as it prepares the file for printing. When it's done, a small image of the base layer of the object will appear in the layer preview pane.

Warm up your nozzle to the appropriate temperature and hit the print button. Obviously, connect to the electronics first. Your printer should start going through the motions. Watch with amazement as the extruder moves to home and then moves around the print bed. It's awesome to see the printer exhibiting printer-like behavior the first time!

Keep close and be ready to hit the on/off switch on the power supply at any moment that something seems not right. It's possible that you will need to restart the first print several times to make adjustments. Usually the nozzle is not the right height over the print bed the first time and some tweaking is necessary.

Don't expect too much from the first print. Work any problems and try to get a good print by ensuring the bed is level, the nozzle is the right height, and the temperature is where it should be. But if the first print looks a little messy, that's still okay. You're finally printing and that's very cool.

Next Up: calibration step four, Getting to Know Skeinforge

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