Z-Axis doesn't work only during printing

Question

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

Answer 1

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!

Answer 2

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.

Answer 3

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?

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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

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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?

Answer 4

I had the same issue with an Ender 3. The threaded rod was not lubricated enough. Adding some lithium grease, applying it evenly, and moving the Z-axis from top to bottom multiple times fixed the issue. I had to recalibrate the Z-offset after that.