This is essentially a new design in that it does not reuse any parts from an existing design. It does however take a lot of its heritage and style from Johan's Rostock design. A huge thanks to all of those whose hard work, knowledge and innovation have brought things this far. Now I hope that I can add my own little increment to the development of the Reprap concept. Mike Paauwe
The first iteration of this machine featured the vertical towers separated by 90° instead of the normal 120°. The reason for this was that it gave a better shaped build area. The build area was more square than hexagonal or triangular. After building the prototype it became obvious that the concept was seriously flawed. In theory the three towers kept the center platform fully constrained but in practice the platform was relying on the torsional stiffness of the arms whenever one set of arms was near horizontal. The result wasn't really usable over a lrge portion of the intended build envelope. So the 90° tower angles were dropped and the design reverted to being a more standard Rostock Delta style 3D printer.
Crossed-Roller Carriage Design
The immediately obvious change is that the design does not use 8mm rod and LM8UU bearings. The Delta-Pi uses a live-loaded crossed-roller carriage design running on the corners of a 19mm square tube. The tube is a sanded finish stainless steel that should be easily available anywhere in the world. The carriage design contains 8 623ZZ bearings and another 2 are used for the idler pulley making 10 per tower and 30 total for the printer. The carriage design features a live hinge and spring beam that allows the bearing tension to be adjusted. The inside of the tubes is open so that it can be used to run wires to the top of the printer.
The arm design has been changed slightly from the Rostock design. The arms use a 6mm carbon fibre tube and the tube is glued inside a clevis. That's not too different but the yokes at each end of the arm assembly are intended to simplify assembly and reduce the number of fasteners required.
The belt can be either S2M or GT2 belt and is 6mm wide. The belt is connected to the carriage by looping a short length back on itself. The belt teeth interlock and a small piece of rod (3mm filament) stops the loop from pulling out. The belt is tensioned by moving the stepper motor.
The design has been done using Solidworks and the source files will be published on GitHub in due course.
Assembly documentation, BOMs and drawings will be posted to GitHub too.
The STL files will be published to Thingiverse as soon as the prototype is successfully built.
The protoype was originally run using the Marlin firmware and later switched to the Repetier firmware.
Current Project Status
As of 25 February. The prototype is assembled and moving. All that's missing is the Bowden extruder feed end. Some new video posted today