In the early days of FDM 3D printing, the RepRap project produced all sorts of weird and wonderful designs. In the video after the break [dizekat] takes us back to the time of the puppet 3D printer and completely dispenses with linear rails in favor of strings.
The closest thing to a linear puppet guide is a sheet of glass against which the top of the printhead slides. A pair of stepper motors drives the print head in the XY plane, similar in concept to the Maslow CNC router, but in this case two more strands are required to keep the mechanism under tension. To properly adjust the length of the string over the entire range of motion, [dizekat] uses a complex articulated roller mechanism that we have never seen before. The cords also slope slightly downward from the spool to the print head, holding it to the glass.
The print bed is also suspended and held with a cord, without being attached to the frame of the printer with a rigid mechanical element. Six strings connected to the sides and bottom of the bed frame hold it in place in a 6-DOF area, running through another pulley arrangement to three more strings and finally to a single crotch strap.
We don’t see any particular advantage in foregoing the linear rails, especially when the mechanisms have to be so complex, but it certainly presents an interesting engineering challenge. Whatever the reason, the end result is fascinating to look at and the print quality even looks decent looking.
A practical advantage of some cable-based 3D printers is their large scale, as they can turn an entire room into usable printing volume.
