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Answered Strange rescaling during print?

Discussion in 'Troubleshooting' started by PropLord, Mar 4, 2017.

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  1. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    The once you know you set the Z steps correctly via the CONFIGURATION.H:

    R1+:
    #define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,800,723.38} // default steps for leadscrews

    R1 w 8mm rods:
    #define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,2560.00,723.38} // default steps per unit for RoBo 3D R1 8mm

    R1 w 5/16 rods.
    #define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,2267.72,723.38} // default steps per unit for Robo 5/16

    If you have say 8mm rods and used the 5/16 firmware you can see that your Z height would be off. If you used the leadscrew version it is way off.
     
    #21 mark tomlinson, Mar 6, 2017
  2. PropLord

    PropLord Member

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    Sorry I haven't updated on my status. I've been sick with a hard core sinus infection all week. Fever and all.

    Thanks again for your help!

    I checked and my default Z step was set at 2560. So I tried 2267.72 and it printed it even shorter.
    Roughly 30mm(X) 30 mm(Y) 25mm(Z)

    So, kind of on a whim I upped it to 2600. It's about 1.5~ millimeters away from a perfect 30mm X 30mm x 30mm cube.
    Do you think I should keep increasing the steps slowly until it comes out as accurate as possible? Or do you think the new "calculations" only work for this particular 30mm^3 cube?
    Do you have any idea why upping it would get closer to an accurate print, if the "correct" number should be 2560?
     
    #22 PropLord, Mar 10, 2017
  3. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    The mechanical bits (thread size, motor size and steps, gear size, etc) do not change from one printer to the next which is what defines those numbers. If yours is not printing correctly then something else is wrong. You are correct that you could tune those numbers to be perfect for that size object, but it will not likely last or work for other sizes.

    You need to make a concerted effort to see if there are any loose mechanical parts.

    Since the Z is your issue there are only a couple of things mechanically to examine.
    - First are the threaded rods tight in the couplers on the shaft of the Z motors (one on each threaded rod)? Try holding the coupler steady and forcibly trying to twist the rod. does it move? If you have the printer on and the steppers engaged (so that they do not want to move) can you turn the coupler on the motor shaft (if should not spin unless the motor is spinning). Check those on both sides. It is not uncommon for the couplers to get loose which allows the threaded rods to not turn (or slip).
    -Second you can tune the stepper driver cards. This is a little more work, but the small daughter cards that mount on top of the RAMPS board drive the steppers. The one(s) driving the Z may need to be adjusted. If the rods are secure we can point you to the instructions for setting the current on the stepper drivers.
     
    #23 mark tomlinson, Mar 11, 2017
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  4. PropLord

    PropLord Member

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    Ok I did the first test you suggested.

    -While holding the Left coupler, I attempted to twist the rod, and it didn't budge. However the Right side can spin up and down, a lot. Quite frankly I don't know how it works, so I put it back in the general position of where it was and didn't try to spin it any higher or lower, in case it damaged it further. But I was able to make to move it up and down about 1 inch.
    (How do I tighten them?)

    -Can I rotate the modules while the printer is active?(print is engaged but paused) yes. I often have to do this to make the print head leveled out.
    (Come to think of it, I didn't really have to do this when I first got the machine. Only recently have I had to do this. Presumably because of the loose rod?)

    "What side is Left and Right?"
    The power supply and On/Off switch are away from me. The "R" on the print bed is "right-side-up."
     
    #24 PropLord, Mar 11, 2017
  5. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Left and right are arbitrary
    Just to be clear you tried spinning the left rod while holding the left coupler and spinning the right rod while holding the right coupler... yes?

    They should not spin at all with that test. Tightening them is done on the coupler itself (there are allen screws on the coupler that tighen it to the rod). If the screws are already tight and the rod still moves (it happens) then you need to either replace the coupler or (my option) just glue the rod in place.

    No, you really should swap the modules with the power off and the USB cable unplugged (the arduinbo gets power over the USB).

    The loose rod will absolutely affect your leveling :)
     
    #25 mark tomlinson, Mar 12, 2017
  6. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    In summary -- if you have a loose rod that is totally your issue and swapping the modules is really not needed. Fix the loose rod before worrying about the modules. They are probably just fine.
     
    #26 mark tomlinson, Mar 12, 2017
  7. PropLord

    PropLord Member

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    Yes, the Left coupler is fine. I held the Right coupler and spun the rod both ways. I didn't hold the Left coupler and spin the Right rod ;)

    I tried tightening the 2 screws that are on the coupler with the Allen wrench. It doesn't seem possible it could be tighter and the rod still spins very freely.

    Should I just glue the rod to the coupler with something like JB Weld?

    I looked at the Robo3d store and the lead screw upgrade is not available. Nor can you purchase replacement parts.
     
    #27 PropLord, Mar 13, 2017
  8. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    One of mine came in broken way back with the beta shipped from the Kickstarter campaign. I simply superglued it in place and it has worked fine ever since (just you know how long that has been -- that was the end of 2013).

    There is not a lot of force acting on the rod which is why glue is a fine solution.
     
    #28 mark tomlinson, Mar 13, 2017
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  9. PropLord

    PropLord Member

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    I'll go ahead and do that then. I am getting super excited that this might fix it.

    Thanks again! I probably never would have though of doing that.
     
    #29 PropLord, Mar 13, 2017
  10. PropLord

    PropLord Member

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    Well... I'm worried that if I get too excited I'll jynx it. (not 100% serious about that, of course)

    But so far, the re-scaling is FIXED! Thank you so much for your help!

    I successfully printed a 30mmx30mmx30mm cube!

    The first 1-2 layers (at 200 microns) do seem to start off a tad too close to the bed though. The machine does the 9 point "check", zooms over to the center, then "zips" just a tad bit down. In fact, the first 1-2 layers don't extrude at all. On the 3rd, it acts as if it were printing the 1st correctly. But of course, it's missing the first 2~ layers.

    What do you suggest for that?
     
    #30 PropLord, Mar 14, 2017
    Last edited: Mar 14, 2017
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  11. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Set your Z offset (the M565 command in the startup gcode) a little higher.

    G28 ; home all axes
    M565 Z-1.0 ; set the offset for auto-leveling mechanism
    G29 ; run auto-level
    M117 Waiting for extruder to stabilize


    The default (-1.0) might be too close to the bed. More negative (-1.1 for example) is further from the bed. More positive (-0.9 for example) is closer to the bed. Tweak it until you are happy with it. A good first layer looks like this:

    https://printedsolid.com/blogs/news/37035715-get-your-prints-to-stick-check-your-skirt
     
    #31 mark tomlinson, Mar 14, 2017
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  12. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    @PropLord there is a code you can use to adjust layer 1 only, that code goes in your startup gcode for the slicer of choice and is a negative offset for the Z auto-leveling grid so in between the G28 and G29 commands in your startup gcode you need to place an M565 Z-1.0 (this is an example only, your actual number may vary and you test by adjusting it 0.1 for each test). The way it works is more negative is further from the bed and less negative is closer to the bed.
     
    #32 WheresWaldo, Mar 14, 2017
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