Mendel90 (by nophead) - significant improvements
Chris Palmer (aka nophead) is an experienced engineer who inspired significant design improvements to the original Mendel design that are still copied and in use today: MendelMax is a Western variant and Chinese (acrylic-based) clones such as by Anycubic and others are commonplace.
- The base on the Mendel90 is a single flat piece. This provides sturdy mounting points as well as preventing "parallelogramming".
- The Y-rods attached to the base on the top, along with two aluminum box section tubes on the bottom of the base, help stiffen the base and reduce bending.
- The uprights are made from three pieces: an upside-down U-shape braced with rectangles behind it. There is thus no possibility of sideways "parallelogramming", nor can the uprights move backwards or forwards.
- However as with all the Mendel designs, due to them being like a "toblerone", one of the base's corners can be lifted up whilst the others remain still on the ground.
The only way to "fix" the reliance on gravity would be to change the design to a cube, as any efforts to provide triangular bracing of the "toblerone" and still maintain that "toblerone" shape would need to go through the actual build area, which would be unacceptable to most operators.
One possibility would be to add a plate (or Ultimaker2-style frame) right across the full height and width of the back, then another board across the top, creating an enclosed space. This would create a rigid cube area out of the back half of the Mendel90, with the front half protruding out. As the front half of the base is supported by the Y-rods (and the aluminium box-section) the whole assembly would be totally rigid in all six degrees of freedom.
In practice, without this design enhancement, despite the Mendel90 needing to be operated on a flat, rigid surface this 3D printer design is actually really good: all of the issues except the reliance on gravity when compared to the original Mendel are solved. Its designer regularly operated it at up to 150mm/s and speeds of 200mm/s have been reported without significant degradation of print quality when using a 0.4mm nozzle.