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Problem: Z-Axis doesn't work during a print. It attempts to work, maybe climbs on the Z-Axis, but screws back down. It whines, too. But, Z-Axis DOES work while not printing. It doesn't matter if the bed and nozzle heating or not, if it's not printing, it works as it should. I don't know what else I can do to troubleshoot this problem.

I have:

  • Changed the Ramps 1.4 board twice
  • Swapped drivers around, bought new drivers
  • Swapped X-Axis and Z-Axis motor connections
  • Cleaned threaded rod.
  • Leveled two Z-Axis threaded rod riders to near atomic perfection.
  • Changed firmware to each of the 3 latest updates
  • Remounted motor so both face same cardinal direction
  • Cursed
  • Changed jumper configurations from 16th microstepper to 8th for more power. No dice. Fried two drivers that way.
  • Dialed and redial and tridialed and quaddialed the driver pots
  • Recalled the Z-motors work while not printing so it isn't the driver pots
  • Cursed again
  • Scoured the web for similar issues
  • Looked for G-code that might limit Z-Axis elevation
  • Died a little. Just a little

Hardware:

  • RepRap Guru DIY Prusa i3 V2 3D Printer Kit
  • Ramps 1.4
  • A4988 Driver
  • Firmware:
    • Marin 1.1.8,
      • 1.1.7 (screen didn't function),
      • 1.1.6 (screen didn't function),
    • RepRapGuru_Marlin_v4,
    • RepRapGuru_Marlin_v2

Additional information:

  • My power supply is the original 12 V 360 W supply with the kit.
    • The 5 amp power in is 12.02 V, the 11 amp power port is 11.96 V and 12.18 V depending on which heater is on.
    • The bed measures 11.50 V and the hotend is 3.4 V
  • While heating the bed and hotend I am using the LCD screen and rotary encoder to move my axes. It works as expected until printing. I have upgraded to an aluminum 12/24 V hotbed from the original PCB.
  • Currently getting Repetier. Will update.
  • The z-axis leadscrew is M5-0.8 mm
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    $\begingroup$ Sounds like a lack of current, or Z-axis steppers not producing enough torque or X-gantry too heavy $\endgroup$ – Greenonline Jul 18 '18 at 7:35
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    $\begingroup$ What about your power supply? Is it producing enough to power the printer when it is powering the heated bed and the hot-end? Did you measure the voltage (drop)? You say it's working fine upto the point that you start to print, the difference IMHO is heating the nozzle and bed, which together take about 75 % of the power of the printer. $\endgroup$ – 0scar Jul 18 '18 at 8:46
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    $\begingroup$ Please explain exactly what you are doing to drive the Z-axis when "not printing" . $\endgroup$ – Carl Witthoft Jul 18 '18 at 12:27
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    $\begingroup$ Please measure for us the following voltages: Board supply from the power supply; the motor's power supply (run a G1 Z100000 F1000 via Repetier). $\endgroup$ – Trish Jul 18 '18 at 12:41
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    $\begingroup$ Just thought of something else. What is the lead and/or pitch of the leadscrews/threaded rods? If the pitch is too high then that could cause the stepper to bork, see this answer: A more aggressive leadscrew will require more torque to drive. $\endgroup$ – Greenonline Jul 18 '18 at 14:15
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I would check the gcode you're generating to make sure it's not full of "bad" z-commands.

Further, I'd take any gcode file you have and manually edit it, leaving in all the initializations, heatings, zeroing, etc., and then delete everything except some z-motion commands. Run that as a test case to see what happens.

I think it's extremely unlikely that the gantry has enough mass to force the z-screws to counter-rotate (lowering the gantry), and you'd see that with power off in any case.

edit

As Greenonline discovered, a bad choice of lead screw might cause the behavior you're seeing. It would be a bit scary if a stock kit such as the one you bought provided high-pitch Z-screws. Better check that out!

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    $\begingroup$ Also check the gcode for how FAST you are attempting to raise the Z. The motor may stall if trying to move too fast. $\endgroup$ – Davo Jul 18 '18 at 14:02
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    $\begingroup$ If the lead of the leadscrews is too large (8 mm) then that could cause unscrewing, maybe? See this comment of Tom's: with an 8mm leadscrew, the weight of the printbed or carriage can overcome the (idle) torque of the stepper, causing the bed or carriage to drop like a rock when the stepper is disabled. This can be rather annoying. $\endgroup$ – Greenonline Jul 18 '18 at 14:16
  • $\begingroup$ Carl Witthoft, I think you are on to something with rogue commands limiting the Z-Axis. Thank you for pressing me to try a new program. Now I need to learn it... So, it works now. The only difference is that I am printing from Repitier using Cora instead of using Slicer to make g-code for an SD card. While, I am happy with the results, I am dissapointed that I still don't KNOW the source of the issue. There must be some command from stock Slicer causing issues. $\endgroup$ – RMF Jul 18 '18 at 18:51
  • $\begingroup$ The threaded rod is a 5mm diameter with a thread pitch of .8mm $\endgroup$ – RMF Jul 18 '18 at 23:06
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    $\begingroup$ If you can post sample gcode files from each source (Slic3r and Cura) , from the same STL file, perhaps we can identify what's messing things up. Quite possibly the internal "configuration data" in Cura's software is a better match for your printer than the same internals from Slic3r . $\endgroup$ – Carl Witthoft Jul 19 '18 at 14:55
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Carl Witthoft, I think you are on to something with rogue commands limiting the Z-Axis. Thank you for pressing me to try a new program. Now I need to learn it...

So, it works now. The only difference is that I am printing from Repitier using Cora instead of using Slicer to make g-code for an SD card. While, I am happy with the results, I am dissapointed that I still don't KNOW the source of the issue. There must be some command from stock Slicer causing issues.

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    $\begingroup$ If you can post sample gcode files from each source (Slic3r and Cura) , from the same STL file, perhaps we can identify what's messing things up. Quite possibly the internal "configuration data" in Cura's software is a better match for your printer than the same internals from Slic3r . $\endgroup$ – Carl Witthoft Jul 19 '18 at 14:55
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    $\begingroup$ I'm not entirely sure if this is an answer or should be a comment to @CarlWitthoft 's answer. As you don't have 50 rep points yet, you can't post a comment. I'll leave this as it is for the moment, so that you can provide Carl with more information, and have a bit of a back-and-forth to solve your issue. However, any new information should go into your original question... or a new question (referring back to this one) if your original issue has been solved. Then, at a later point, once the dust has settled, I'll convert this answer and carls comment to comments under carl's answer. $\endgroup$ – Greenonline Jul 20 '18 at 7:18
  • $\begingroup$ I'm converting this answer to a comment. Even though you have less than 50 rep points you can comment on Carl's answer, as it is an answer to your question. See the "special Note" on the first answer here: meta.stackexchange.com/questions/214173/… $\endgroup$ – Greenonline Jul 26 '18 at 15:34
  • $\begingroup$ Actually, after re-reading this answer, it could actually be an answer, if (as Carl suggests) you edit this answer and add/post the G-code that didn't work and then the G-code that did work, that way the "incorrect commands" could be identified, and then you will hopefully discover the source of the issue. Doing that might help other people with the same or similar issue. If you do this and then flag your changes, using the flag link under your answer, then I can undelete your answer. I hope that you understand :-) $\endgroup$ – Greenonline Jul 26 '18 at 17:26
  • $\begingroup$ I've undeleted this, because I couldn't work out if it was an answer or not and, as it has been playing on my mind for a few months, I decided to err on the side of caution. I sincerely apologise for any confusion :-) $\endgroup$ – Greenonline Sep 11 '18 at 22:19
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From your comment

the z-axis leadscrew is m5-.8

I presume that your lead is 8 mm? You don't state whether it is a threaded rod or a leadscrew, so I will presume that it is a leadscrew.

If so, then I would suggest that you choose a different leadscrew, one with a lesser lead, say 2 mm or 4 mm. This is because, for a 8 mm lead, the stepper motor has to lift the X-axis gantry by 8 mm upon one rotation, which requires four times the amount of work that would be required to lift the X-axis gantry by just 2 mm if a rod with a 2 mm lead is used.

So you need to either:

  • Change/upgrade your stepper motors to ons with more torque, or;
  • Change the rods, for some with a smaller lead.

Depending where you are in the world, one option may be cheaper than the other.

If you are going to upgrade your rods, then change from a threaded rod (if you are using one), to a leadscrew, as they are much better quality, have less friction, more precision and less wobble. However, you may also have to change your [rotary] fittings, i.e. the nut that goes around the rod - although you would have to do that anyway if you change your threaded rod for one with a lesser lead. Also, many threaded rods, and leadscrews, come with the rotary fittings included.

Also, you state that your threaded rod/leadscrew is M5. Again, if you are going to have to change it, it might also be worth changing from M5 to M8, see Lead screws - M8 instead of M5?


For a more in depth explanation, see this answer to the question, Would using a leadscrew with 1 or 2 mm lead, en lieu of 8 mm, result in a better printer? Here are some highlights:

A more aggressive leadscrew will require more torque to drive. We have one kit printer we bought a couple years ago that has an overly aggressive multi-start leadscrew for the z-axis. The small motors included in the kit do not have the torque required to reliably start upward movement of the carriage, leaving it sitting there skipping steps until the carriage is given a little upward nudge to get it going (no, it's not a lubrication issue or a driver that needs turning up).

and

(As Tom points out) An 8 mm lead can result in the weight of the X-axis gantry (especially in a P3Steel) overcoming the idle torque of the stepper. As a result of this, the X-axis gantry can end up sliding down the leadscrew, in particular at power down


Note that there is a difference between pitch and lead:

  • Pitch is the distance between adjacent grooves on the rod, whereas;
  • Lead is the distance travelled along the rod upon one rotation

The difference depends upon the number of leads, or starts that your threaded rod has.

From What is the difference between screw pitch and lead?

Pitch versus Lead

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  • $\begingroup$ Learned something new! Thank you Greenonline! So, I have threaded rod that is m5 .8. It is 5mm wide with with a pitch of .8. The kit is from reprapguru.com. I have had so many issues with it, missing parts, terrible documentation, certain prusa firmware not functioning at all (1.1.6, 1.1.7). I do not recommend it. Original firmware broke my endstops off. Since this is my only printer, I assumed the aggressive nature of the machine was typical. I now have some office rearrangement to allow the printer to remained connected to the computer. $\endgroup$ – RMF Jul 18 '18 at 19:07
  • $\begingroup$ Just to clarify, is that a pitch of 0.8 mm, or 8 mm? 0.8 mm sounds about right, but it is the number of starts that is important really... How many starts does the rod have? 1, 2 or 4? Regardless, it is a shame that your printer seems a bit of a 'mare. However, I'm sure once you get used to it, it will be fine :-) Glad you sorted your problem anyway. :-) $\endgroup$ – Greenonline Jul 18 '18 at 19:47
  • $\begingroup$ Yes, its a pitch of .8mm. What is the number of starts? How does this affect Z movement? The supremely unfortunate part is that it used to work. I've had the printer for a few months, it was out of commission for a month or so while I was replacing parts and diagnosing syptoms. It was never easy, but it worked well enough to keep. The issue may be from a Z-axis speed increase by accident, but reflashing and deleting and installing new slicer didn't fix the issue (which would make sense if the custom files were stored elsewhere). $\endgroup$ – RMF Jul 18 '18 at 23:11
  • $\begingroup$ After reading up on lead screws, I will upgrade eventually. Until then, the machine works with cora. Thank you for your help and knowledge. $\endgroup$ – RMF Jul 18 '18 at 23:12
  • $\begingroup$ @RMF - The number of starts, or leads, is the number of individual threads. Referring to the pic in my answer, look at the end of your rod... how many entry points are there on the bottom? It could be just one, or maybe two, or possibly four. That number is the important number of starts. You then multiply the pitch (in mm) by the number of starts to get the all important lead (in mm). Does that make sense? $\endgroup$ – Greenonline Jul 18 '18 at 23:15

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