Y axis grinding and missing steps

[cturner]

Just got my carve king built and was running my first job. It uses three end mills and was created on aspire. After homing and resetting to zero at the corner, the first cut went perfect. I then changed the bit with the router still in the mount. I ran the second cut and the y-axis moved to the first position fine. While moving to the second position it made a grinding noise then missed steps putting it in the wrong position. I commanded it back to zero and it was off by about 10mm. I reset zero again to the corner and tried again. The same thing happened in the same incorrect position. I tried a third time and the position was still incorrect but in a different place. I am not sure if this is due to the y and a couplers not moving at the same time or what. There is no binding when moving manually. The v-wheels appear to be tight. What else should I check?

[Derek the Admin]

Hey, we’ll help ya out. I’d like to clarify. Are you saying for sure that the couplers are moving at different speeds or are you supposing that as a cause?

I would make sure both couplers are tight to the shaft and to the screw. If one is slipping it will cause this.

Did you resquare the gantry after the first time it did it (by moving one coupler but not the other)?

I’d also confirm that both drivers have good voltage on them (0.65V DC).

This can also be a drive line alignment issue. If the motor, lead screw, and idler block are not well enough aligned you will encounter binding. Excessively tight v wheels can cause it too. You can isolate mechanical binding from the electrical causes by pulling both Y motors and putting them on the table. Note their positions with a sharpie and command 8mm movements. You should see one full rotation of each motor, timed the same. You can then increase the step size to multiples of 8 and check the same.

Also, bad settings can do this. Please post your settings by typing $$ in the command line then press enter.

[cturner]

I resquared the gantry and tried the Sharpie technique. Both couplers move the same amount during tests. I tightened up the couplers just in case. I still got the same result. During the run the marks on the couplers become misaligned by about 1/4 turn. This happened after it Sounds like it binds. The alignment looks good for the lead screws. Micrometer shows the Y lead screw to be 5-7/8 “ from floor to center line at each end and the A lead screw to be 5-15/16” from floor to centerline at each end. Finally I loosened the v-wheels slightly. I tested again using multiples of 8. All is good at small numbers. At 320, the right coupler is perfectly aligned with the mark but the left is off. The stepper motors measure between.65 and .66. Any thoughts? If it would help I can video the y axis test and the cutting run I am trying.

[cturner]

Missed the part about settings. I verified that they match the instructions with one exception. I chose to install the corner blocks per page 20. $131=432 causes the gantry to hit the corner block so I changed it to $131=420

[Derek the Admin]

I'd like to see the entire list of settings please. I also think it's best to pull the motors and run them on the bench to confirm equal rotation over a longer period. I do believe this is a mechanical bind though.

Also, that setting change you made will only work if you enable soft limits (setting 20).

If it is indeed mechanical, I'd guess a vhweel or two is too tight, the Y rails aren't parallel to one another, the button cap screws that are on the part of the Y bearing plates that face the extrusion are dragging on the rail instead of having clearance in the slots. V wheels clocked to one extreme or the other can cause the last case.