01 - Drive Mechanism (Z axis)

Post date: Oct 6, 2015 2:57:40 AM

In some ways, the SLA printer design is simpler than the FFF, one example is only the Z axis requires motion control. For this printer the Z axis was created from salvaged and printed parts.

Additional parts had to be designed around the salvaged lead-screw, nut, and stepper motor. Some brackets were made (FFF - PLA) to hold each end of the lead-screw to the 45x45 extruded Aluminum. In this instance 5/16" Wiz nuts were used inside the channel of the aluminum to receive the 3/4" hex head bolt. Speedy metals 8mm drill rod was used as the guide rods connecting between the brackets.

Here is a shot of the Tinkercad design for the brackets:

And after printed and mounted:

The nut assembly needed a bracket to mount bearings in for guiding the build platform. An arm will be mounted to the bracket.

The bracket:

The rapid-prototyping trial-and-error approach (heavy on the error...)

The Z axis, ready for the frame.

Several issues became apparent with this implementation including: 1) the parallel alignment of the lead screw and guide rods leads to weak side-to-side twisting stability, 2) the short vertical amount of support offered by the linear bearings means flexing vertically. In speaking with a mechanical engineering friend, he suggests more of a rail design, not to use linear roller bearings as a means of support. Short of that was to use an upper support with at least a 45 degree connecting arm. The quick and dirty tweak was to print another bracket similar to what is below the arm making a "sandwich". The arm could have been made more stable but this whole project has been an experiment of sorts. Note the re-design of the way the bearings are held in on the upper bracket (they are clamped in place rather than separate housing pieces). Other options for more stability are larger diameter rod, push or pull the rods forward or back so they are not in line with the lead-screw, or to use smaller, lighter material (80/20 - 1010) and/or shorten the arm.