Erik de Bruijn along with a newly formed Dutch RepRap group have put together this new design for a low cost RepRap alternative. The stated goal of their blog is “designing/developing an easy to build low cost 3D printer with a small form factor but large build envelope.” Erik has invited everyone to comment on this beta design. It’s interesting to see their progression of prototypes in their second blog post.
The very nature of FDM1 means that the robot will only move the Z axis a little bit every once in a while. One of the design drawbacks to the Darwin was that the heavy extruder head (motors, gears, heating elements) were so heavy that the entire robot would rock or vibrate with the lateral XY movements. MakerBot got around the heavy extruder head problem by moving the platform in the XY and moving the extruder head only up and down. This design decision isn’t without it’s tradeoffs, however. One downside is that their build area is much smaller than a Darwin. Another downside of the MakeBot design is that once the object being built reaches a sufficiently large volume or height, moving the object around quickly on the XY platform causes it to vibrate, shake, and become somewhat unstable.
One of the main improvements inherent in the Bowden extruder is that it allows you to take the heaviest parts of the extruder head, separate them from the rest of the extruder head, and move those heavy pieces to a different location. Using a Bowden extruder makes a Darwin style robot much more feasible – the small moveable print head won’t have the mass to cause the robot to become unstable.
It seems that combining either of the X or Y movements with the Z probably won’t matter all that much, since the Z axis will only move about 0.33mm or so per layer and the Z axis typically doesn’t operate at the same time as either the X or Y axis. Combining the as the new RepRap version II, Mendel, design shows us that combining the Z axis along with either the X or Y axis, but not both, can lead to a very stable configuration.
What I like about the Ultimaker design is that it would appear to incorporate some of the best parts of the MakerBot and Darwin designs. It appears to have a bolt/nut/T-slot MakerBot style assembly structure using thin lasercut wood pieces for the body. I found these parts to bolt together very quickly. Contrast this to the Darwin/Mendel structure using lots of nuts and threaded rod and printed plastic parts to hold it together. At the same time, by making use of a Bowden extruder and the Darwin body shape, it appears to be able to use most of the interior volume for printing.
I suspect it probably uses fewer parts than a typical Darwin, but I can’t be sure. I also have to wonder about the cost of lasercut wood versus the cost of nuts and threaded rod.
Nice find RepRap Log Phase!