This printer is designed to be very easy to assemble, with a minimum number of parts. It is very easy to use and easy to hack. It has a smaller footprint and larger print area than its predecessor, the Aluminum Mendel. It is very precise and efficient. The tradeoff is that it requires some machined parts that may be hard to source if you do not have access to a vertical mill. For this reason, it is not a good choice for beginners. The y and z axes use machined UHMW inserts that slide directly on the aluminum extrusions. This gives a rock-solid print bed with very low friction. All forces acing on the printer are carefully balanced for smooth printing. The low mass extruder is very precise for accurate, clean prints.
See assembly drawings and BOM. Add a bed heater and power supply of your choice. I do not yet have the nuts and bolts on the BOM. I included dxf files for all the parts made from aluminum plate. You can upload these files directly to emachineshop.com and they will laser cut them for you. Get two zBrackets. You will have to do the countersinks yourself. These parts are much cheaper if you can get several people together and order multiple sets. I have included prints if you want to make the parts of aluminum manually. The extruder plate is the hardest. Print out the stl alumPlateV2 and use it as a drill template.
It is possible to print the slides, although they have more friction than UHMW. For this reason, I have included stl files for them. Use silicone spray to reduce wear and friction for printed slides.
The flexMendel follows a few basic design principles. It will be helpful to understand these principles when assembling the printer. The axes are only minimally restrained, there are many places where components need to float or flex. Reciprocating masses are kept low, and forces are carefully balanced. The frame is the sliding mechanism, there is nothing to align. This makes a very efficient, precise machine.
The Y carriage is constrained in the y axis only by the two slides on the right side. They are loosely constrained in the +z direction, gravity holds the carriage down. The single slide on the left floats in the x and +z. Its function is to support the print bed on the left side. If the right y slides are a little loose, you can angle them slightly. The y belt tension helps prevent yaw in the y carriage, and should be run pretty tight.
When the x axis ends are assembled with the smooth rods, care should be taken to make sure that the rods can slide on one end. The x ends are held together by the x belt tension, and can move in and out slightly. This prevents binding of the z axis if the z frame pieces are not perfectly parallel. The top bushings on the x carriage constrain the extruder in y and z. The bottom bushings only constrain the extruder in y. They can flex in z to account for any variation in the distance between the smooth rods.
The threaded z rods are tightly constrained in z by the thrust bearings in the top z rod brackets. They can float slightly in x and y. The nut cap that retains the 8 mm nut in the x ends must not be over tightened or the nut will bind. It should be free to align with the threaded rod. The flex couplings specified should be used, or a substitute that has both radial and axial compliance and uses set screws rather than clamping the rod. The common spiral aluminum couplings have no radial compliance. Finally, the z motor mounts can flex slightly in x. Install the z motors and couplings with the top z rod brackets loosely fastened. Then, run the x axis up to the top and tighten the top z bracket bolts.
Finally, the extruder shaft must be able to float slightly. With the shaft installed in the partially assembled extruder, insert a short length of filament and the shaft will align itself properly. Use the pinch roller if necessary to hold the shaft in place. Then install the large gear on the shaft, leaving approximately 0.5 mm clearance between the gear and aluminum plate. This will prevent twisting of the filament.