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(crickets)
In addition to my calibration puzzle, I’ve noticed something odd about axis movement. Jog commands (via Printrun for Mac) for Y and Z move to the proper extent. Jog commands for X only go half as far as they should. (G0 X200 will only move halfway across the build plate.) It’s not a problem with steps-per-axis, or microstepping, since the Theta and Psi wheels move at the same rate when I do a G28, Home All.
Any suggestions greatly appreciated. (Other than “go build a rectangular printer”.)
There are many ways to configure things incorrectly, or perceive them incorrectly. I seem to have encountered most of these. 🙂 Ignore the “confusion” part of the previous post. Not that I’ve de-confused myself or anything… I’m just the Perfect Idiot who has come along to flush out alternatives that are Not Perfectly Obvious. Perhaps by blundering along, I can collect a set of “principles of operation” that may not be evident to the new observer, who will be freed to go forth and make NEW mistakes. Here are a few samples.
Jogging +Z should increase the distance between the nozzle and the bed. The Z stepper will move CCW, the bed will go down.
Homing the Z axis should send the bed downward, until it reaches Manual_Z_Home_Position -or- hits the hardware “Z MAX” endstop.
Sending an M114 code (through the interactive text line) should cause the RepRap machine to report its current X, Y, Z and E coordinates to the host. SCARA diagnostic values will also be reported.
For today’s chapter, I have one observation about calibration, and a lot of confusion.
OBS #1: The graphical flowchart in Morgan-Calibration-Guide is puzzling if viewed alone. If you examine it in combination with reprap.org/wiki/G-code, it will make a LOT more sense.
And the confusions:
If “Bed 0 is at the top right corner when viewed from the front”, what are the coordinates of the bottom left corner? [x=205, y=205] , or [X=-205, y=-205] ? If it is the former, as I suspect, then I need to turn my mental perspective around, and imagine that I am sitting on top of the threaded rod, with the print bed spread out in front of me. (0,0 at my left near corner, 205,205 at far right corner.)But then I am in conflict with the jog controls of Pronterface, which moves the wheels counterclockwise toward the MAX end stops when I click the +X or +Y buttons. 🙁
I think that I am missing the Big Picture. Help?
[Section 3, page 72]
To flange, or not to flange, that is the questionQuentin’s instructions on the Wiki suggest that one should use a F608Z bearing, a detail that is missing in the magazine. If you use a normal 608Z, it is possible for the bearing to get pushed too far up into the center bore of the drive wheel. And then the Theta wheel will be to low, and not line up with the pulley on the stepper.
Quentin has helpfully provided a small hole in the side of the Theta drive wheel part. You can use a short M3 screw to affix the wheel to the 22mm tube.
[For section 1, page 71]
Following the instructions literally will lead you to a physical impossibility. If you thread the nut onto the shaft, and then slide on the drive wheel, you can’t thread the next nut into its socket.It’s best to START by inserting the two M8 nuts into the Drive-wheel-rod-mount. I used a woodworking clamp to press them squarely into the hexagonal sockets on the drive wheel. By doing this first, you will be able to thread the complete wheel assembly (nut+wheel+nut) onto the threaded rod.
[For section 4, page 73]
The 3D printer at my makerspace seems to have some calibration issues. When I printed the “Z Mount Bottom” and “Z Mount Top”, they came out undersized.Rather than wrestle with the calibration, I consulted the part PDFs, and made my own parts out of acrylic. I used a milling machine to cut the holes, and now the steel rods are VERY precisely positioned at 175mm apart, and aligned with the drive-pipe assembly.
[For section 6, page 74]
Many people notice that the top platform does not end up parallel to the bottom platform. Quentin says that’s OK – the only thing that matters is that the print platform should be perpendicular to the drive rods and drive-pipe assembly.Speaking of those notches….
I was looking at the Configuration.h file today, and I noticed that the inner arm length and outer arm length are established right there at the top. It set me to wondering – If I wanted to have a larger build platform, would it be as simple as building appropriate arms (say, 200mm), changing the parameters, and recompiling the firmware? My hopeful self is encouraged, but my cynical brain, scorched by long experience, bets otherwise. (Optimistic self also wants to paint 3m by 3m pictures in the street using the SCARA mechanism.)
I’m in Pittsburgh, PA, USA. I think the tubing issue is easier than we have been thinking. Copper plumbing pipe will meet our needs, and is easy to get almost anywhere.
My hands-on research shows that hard copper tubing, nominal 3/4 inch, has an OD of 22mm. Either Type L or type M will work, the only thing that matters on this tube is the OD.
Also, nominal 1/2″ Type L (blue lettering) will work fine, it holds the hex nut firmly. Type M (red lettering) is too thin – the nut slides loosely into the tube.
Oh, don’t get me wrong, good sir. I have a full appreciation of the metric system, and the difference between “measurement systems” and “manufacturing standards”. (Happily, I am not involved in the manufacture of British bicycles, which I hear is a world of its own.)
My desire to learn the wall thickness of your 15mm pipe is driven by the wish to benefit from your proven and successful experience.
I personally think that the development of an SAE-based branch of the Morgan design would be a waste of resources. “Why invent a square wheel when a perfectly round one already exists?”
Stepper Motors – the article calls for 2 each two types – 200 step and 400 step. There’s an inference that these need 2 types of Pololu stepper driver cards – 2 each “low-current 1/16” and 2 each “high-current 1/32”. What’s left unsaid is the torque specification for each motor, and where on the machine each type goes. Any suggestions?
(It’s pretty easy to guess that Psi and Theta are driven by the same type, and this infers that Z and the extruder get the OTHER type.)
Thanks, Quentin. Those pointers helped a lot, and the illustrations in the RepRapMagazine article help VERY GREATLY.
…. but leads to more questions. 🙂
1) The article specifies two types of NEMA17 stepper motors, “200 step” and “400 step”. It’s easy for me to imagine that two of ONE type are used to drive the Psi / Theta shafts, and presumably the SECOND type are used for Z and the Extruder. Can you please recommend the TORQUE specifications for each position on the printer?
2) I am a foolish American, so I want to wrestle with the “15mm copper tubing” issue again. Can you please tell me the -actual- ID/OD for the tubing you are using? Wikipedia has a lot to say, suggesting that our nominal 1/2″ type L or type M copper tubing might apply, being 15.875mm OD
http://en.wikipedia.org/wiki/Copper_tubing
