It’s rare these days that a new FDM printer hits the market that piques our interest, but the [Kralyn]’s Positron did it. (Video, embedded below.) It prints upside down and is packaged in a filament box while still offering a print volume of 175mm x 176mm x 125mm.
In contrast to most 3D printers, the hotend and the XY gantry are mounted directly on the base under the build plate. You might assume that a printer has to gravity extrude plastic to function properly, but the real action is in smoothing the layers of plastic. It seems it could even improve bridging as the hotend helps the plastic extrude. A clear glass build plate is used with the same heating strips found on the rear windows of most cars. This allows the user to continue to see the part and has the added benefit of being able to quickly identify bed leveling and adhesion issues.
Another interesting side effect of this arrangement is the rigidity. The XY portal does not have to be hung in the air with the heavy hotend, but can be mounted directly on the thick aluminum base plate. It uses an H-Bot style gantry with Synchromesh control cables instead of belts, eliminating the risk of belt twisting. In order to achieve the best possible print volume in the size of a filament box, the gantry axes are arranged diagonally above the base plate. The Z-axis can be placed separately and flat on the printer, and uses the linear rails to keep it perfectly straight and vertical during assembly.
To adjust the height of the hotend to the space available, the filament comes in from the side and the melted plastic makes a 90 degree twist before extruding it. It took [Kralyn] a few tweaks to make this work properly but the large volume of the melt zone allows for increased flow. However, we suspect that this could also make hotend maintenance a little more difficult. The only other concerns we have are limited visibility of the printed part and the possibility of plastic parts falling into the gantry mechanism and blocking it. As far as compact folding printers are concerned, this is probably the best design we’ve seen so far. The design is licensed under CC BY-NC and all design files are linked in the video description.
thank’s for the Tipps [IraqiGeek] and [Jasper Jans]!