As a part of my internship at sub-edge Technologies I was involved In the design of a low cost 3D cartesian printer. we try to address some issues faced in traditional cartesian printers, one of them would be Bed- Levelling problems. Instead of using a auto-bed leveling scheme I decided to eliminate the cause of level creep – the inability to keep two Z motors in sync. NEMA 17 motor manufacturers publish the Error Rate for their motors. While that rate is small, it accumulates on a printer. Indeed, auto-bed leveling techniques increase the effect since they are constantly moving the Z motors across every layer. The solution is to have One Z motor physically synced to two rods. Therefore the target would be to build an easy to assemble, compact Cartesian printer that retains a level bed once it has been set.
CAD model of the First Prototype
X axis pulley belt system.
Mount of X carriage to the X extrusion. It consists of two Eccentric spacers on the mini-wheel so that the carriage moves smoothly with no wobble.
The printer has only one Z axis motor. That motor runs the left threaded rod through a pillow block at the top. epThe top of that rod has a pulley mounted that engages a GT2 timing belt to run the right threaded rod. The right threaded rod has a pulley mounted on top and is held in place with a pillow block top and bottom. The pulley on the Z axis motor is 16 tooth driving a 20 tooth pulley on the threaded rod, a 4:5 ratio reduction. The threaded rod is an 8mm with 1.25mm travel per rotation. With the 4:5 reduction, each revolution of the stepper motor results in a 1mm lift on the Z axis.
The beauty of this is that the Z axis can run all the way down to 0.005 resolution while moving only full sts on the stepper motor totally eliminating microstepping from the Z axis resolution. No matter what the layer height is, it will always be in full step increments, guaranteeing that all layers will be exactly the same height, which microstepping can not guarantee.
8mm threaded stainless steel rods (Z-axis) with nylon nuts was used because 2 acme screws required too much torque, heat and sound for one NEMA 17.
Y axis, base plate and pulley assembly system
The total workspace size is
205mm X 205mm X 180mm
Parts being printed by the prototype.