This is the tenth post in a series detailing my efforts to build a RepRap Mendel, an open source 3D printer. For the rest of the series, see here.

Introduction:

When I last left off, the hotend for the Mendel had broken, necessitating a replacement be ordered. This was installed and the printer was back in working order. I was able to move the print head, and even performed a successful extrusion test, as shown below (note the healthy coil of white, rather than blackened, plastic)

Skeinforge, SFact, and Start.GCode:

I headed over to Thingiverse and searched for a simple object to print. For my first part, I decided to bring my 3D-printing experience full-circle. The wonderfully talented Marc Raiser printed out all of the plastic parts I needed to construct my RepRap on his Makerbot Cupcake. So for my first test print, I was going to print his Hackintosh logo design. It’s fairly simple while simultaneously being a good test of the printer’s movement capabilities.

I downloaded the .stl file and opened it in pronterface, which promptly set to work “skeining” the model (slicing the 3D model into layers and translating each layer into a series of motions for the printer head). When the skeining was completed, I hit the print button. While the print head did move, no plastic was being pushed through the extruder.

I headed over to the #reprap IRC channel in search of a wise person who could help me address this problem. The sages at the reprap channel helpfully pointed me to a simplified version of Skeinforge known as SFact. In order to convert a 3D model into a series of commands useable by the 3D printer, a software program is used. At the time of this writing, Skeinforge is by far the most ubiquitous program for this purpose, sitting at the heart of 3D Printer toolchains such as RepSnapper, Printrun (pronterface), and the ReplicatorG software that powers Makerbot’s printers. Unfortunately, Skeinforge is very complicated, and not well configured by default. One of Skeinforge’s configuration settings is to enable the printer extruder, and for reasons unfathomable to this author, this setting is not enabled by default.

SFact is a simplified version of Skeinforge, with default settings that are printer friendly and produce fairly good print results. I downloaded SFact from the github repository, and proceeded to replace the existing Skeinforge folder from my Printrun directory with the newer SFact folder. The default settings for SFact seemed to work quite well, and a dry run (running the printer without any plastic filament inserted) showed the print head moving in a correct and satisfactory manner.

As a quick aside, I should mention start.gcode. This is a special file which includes commands that are appended to the beginning of a compiled model. These commands are run prior to the remainder of the model being created, and include things such as resetting the extruder and homing the printhead to an origin point, among other things. Start.gcode can be found in $PRINTRUNDIR/skeinforge/skeinforge_application/alterations (where $PRINTRUNDIR is the location where the Printrun printing suite was installed), and may contain any of the GCodes detailed in the RepRap wiki.

Test Prints and Heated Build Platforms:

The dry run having worked properly, it was time to try a real, live, bona fide test print. I loaded plastic into the extruder and issued the print command from pronterface. The machine sprang to life, homing to an origin position, and began pushing plastic correctly through the extruder.

But… the plastic didn’t stick to the build platform. My build platform is a 5mm aluminum sheet covered in Kapton tape. Unfortunately, for plastic to stick to the surface, the surface needs to be heated. My Mendel-Parts kit did come with supplies to heat the build platform, so it was time to build that.

The RepRap Mendel build saga is ongoing, so stay tuned for future updates! In the meantime, be sure to check out the other posts in the build series, and check out the latest photos from our flickr set.