Trouble with M8 Threaded Rod Upgrade - Z Axis Locking Up

First post. I've learned so much from this forum, so I'm hoping that you guys can help me. I have an original Kickstarter printer. This weekend I upgraded to M8 threaded rods, and a E3D v6. No issues installing the new hardware. I updated the firmware using Mike Kelly's files for my type of printer with no issues (z-step change to 2560, max temp increase, thermistor change to 5, etc.). However, my z-axis locks up and makes a grinding noise when Auto Home is selected on the XXL LCD. I can manually move the axis using the XXL LCD with no issues. The new M8 threaded rods are well lubed with 3-in-1 oil, and work perfectly when manually controlled with the XXL LCD. I can manually move the Z-axis through its full range with no issues, but when Auto-Home or a print is started, it immediately locks up and makes that awful noise.

In my troubleshooting, I find that if I re-flash the 2560 steps per mm, back to 2267.72 (I know this is for 5/16 rod, but just troubleshooting), the Z-axis works perfectly again. Am I missing a second line in the firmware that needs updating for the M8? I'm only updating the one line in Configuration.h #define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,2560,723.38}. Is there another place that needs the 2560 value?
Anyone else experience the z-axis binding when moving to the M8 threaded rod?

 

Might be worth trying to increase the Z stepper drivers potentiometer to increase the current going to the motors. The smaller step size might make it require a bit more torque.

http://reprap.org/wiki/Pololu_stepper_driver_board

 

Mike, thanks for the fast response. I had this thought, but dismissed it since the Z-axis works perfectly when using the manual axis moves via the XXL controller. If the Z-stepper driver performs perfectly on a manual move, it should be providing enough current for automatic moves as well. Is my logic correct, or would something in the firmware call for a lower stepper driver duty cycle during the automatic versus manual moves? I hate to bump up the pot if its not needed. I'm willing to try it if its my only option.

Raider Power (BSME '99).

 

I got that as well while trying to capture my Z threaded rods. It would work during manual controls but while printing it would get stuck.

I think it has to do with microstepping resulting in less torque, so for the fine layer movements it's not getting enough to overcome the stiction.

Measure the V_ref before tuning the pot. If it doesn't work you can always go back to the old value.

Also just to be verify the threaded rods have been lubricated?




(BSME '08)

 

Mike, you nailed it. Adjusting the Z stepper pot did the trick. It only took a very slight adjustment to do it. I've run about 20 Auto Home's to verify. Looks like I'm good to go. Thanks for the help.