Variations on a theme...

(Assembly of the McWire Variation began around November 8-9)



Mostly productive weekend. Here’s the long and short: X and Y stages are fabricated and assembled. I ran into a few mountains that turned out to be mole hills and a few hills that turned out to be mountains.

The first issue I came across was printing the stage templates. Evidently, Adobe scaled the first run to fit within the printer boundaries. I cut the pieces out, drilled the holes, cut the rails and support brackets, assembled all…and the stage was too small. Measure twice cut once…oops. I new I should have tried to find a .DXF viewer to get actual dimensions and fab that way. Oh well, I have no one to blame but myself. Rather than scale the entire project down, I bought a new piece of plastic, reprinted the template sheet (on an 11x17 sheet no scaling), re-cut, re-drilled, etc.

This brought me to my next opportunity! Either the new template was too big, or I really have trouble finding a center. Long story short, the PTFE bearing centers were off. Not by much (again, probably due to Adobe scaling to the printer boundaries, grrr), but enough to warrant the need to expand the center to center dimension on the rails. This meant I would have to re-drill the ¾ pipe that the X stage rails attach to. As a side note, I was also having some difficulty getting the X stage rails square to the stage. I think that this was due in large part to the way the pipes fit in the elbows. Say you have two pipes, each has 1 inch of thread. “Pipe A” will thread into “Elbow A” 5/8 of an inch. “Pipe B” will thread into “Elbow” B ¾ of an inch. Since the dimensions for the X stage rail connection points are taken from the threads at the opposite ends…you end up being 1/8 of an inch out of square in the above example. So in rethinking this portion, I decided to abandon the pipe as support for the rails. Rather, I cut a ¾ piece of plywood at approx 18-1/4 inches, the inside to inside dimension of my X stage rails when attached to the angle supports. I took a left over 2x6 from another project and ripped two pieces to length as stand offs for the assembly so the X stage motor would be in the air, as it would have been if the rails were attached to the pipe. I also needed to route the plywood on the inside edge of the bearing rail, so the inside bearing (which sits about ¼” lower than the outside) would have free travel. While eliminating the need to re-drill the ¾ pipe (which was tough for me to begin with), this also made it easier (as in near impossible to screw up) to square up the rails. I oversized the mounting holes on both the angle support and the rails where they attach, and that made up the difference for the PTFE bearings. With this latest hurdle behind me, I had a new methodology towards the fabrication of my bot…test fit, test fit, test fit. Drill nothing…cut nothing…until everything had been verified. This, of course, is something I should have been doing from the beginning.

With the X stage more or less complete, I moved onto the Y stage. Having the forethought to check all hole dimensions before cutting and drilling, the Y stage was considerably less hassle/rework/etc. However, it should be said that for some reason, my Y stage spring bearings ran into the X stage. So I shimmed the PTFE bearings with washers (which I will most likely replace with a different spacer) high enough so the bearing bolt/nut would clear the X stage.

With the two frames/stages assembled, it was time to mount the motors and drive screws. This part (I am glad to say) went off without a hitch. I did notice that unless the drive screw is touching the rail support, the stage would not move. I attribute this to the tubing not having a secure enough hold on the screw. I’ll most likely dab a dollop of silicon caulk to the screw and reattach the tubing. Leaving it “unglued” to the stepper motor, it should still act as a motor coupling and slip (on the stepper side) if it gets into a bind.

Z stage is comin' up fast, I will post more on the progress hopefully later this week...

-Rick