New PM728VT cnc conversion backlash issue

[Wildcat]

I ordered a 728Vt with the precision ballscrew kit from PM last month. After a shipping misshap that crushed the top of the crate along with the fan and shroud for the spindle and a missing ferrule on a oilier line I finally have it going. PM was great and replaced the ferrule and shroud and fan promptly.
I put the ball screw kit in and made a new box for the rear to house the electronics.
Running a ESS with C25 BB and a C41S PWM board for the Spindle. Mach3 for the software.
I have Leadshine ES-D808 Easy Servo drives which are controlling Nema23 and 34 steppers with encoders.

After tramming it in and setting my steps per I went to check the backlash. I have 0.0023" in the Z, 0.005" in the X and 0.006" in the Y. After paying $1100 for precision screws from PM I feel a bit cheated. Do they not preload these things? Now I have to pull the machine apart again to fix it.

Extremely disappointed with this so far.

 

[GB21]

I went down this same road and had to pull the machine apart. I know how you feel.
I sent PM the video they would not send me replacements or anything so I made shims to fix the issue. The worst one had a 0.006 gap.

 

[GB21]

Here is a link to the shims I made with fusion. I cut a bunch of them of various thickness on my cnc router or you can even print them on paper and cut with scissors. If you have a laser that might work too. Hopefully it will save you some time.

Fusion

Share 2D and 3D design files and project files with anyone.

a360.co

 

[Wildcat]

I went down this same road and had to pull the machine apart. I know how you feel.
I sent PM the video they would not send me replacements or anything so I made shims to fix the issue. The worst one had a 0.006 gap.

Thanks for the link to the shim. You would think that PM would at least provide shims since the crap screws are not pre loaded. This is ridiculous for the money one pays for these things. I had less backlash with the stock acme screws that came off it.
Any pointers on figuring out the proper thickness of shims?

According to PM they stated
"not one single backlash complaint so far has actually been caused by the ball screw" Which is technically true. I am having issues with the ball nut not the screw.

thanks again

 

[GB21]

Its trial and error. I added shims until I felt binding while turning the screw by hand and backed it off a thou or half thou at a time until smooth. I am not sure if its the correct method and definitely not ideal but my lash MUCH lower and its been running great like this with heavy use since 11/2021

 

[Firebrick43]

Thanks for the link to the shim. You would think that PM would at least provide shims since the crap screws are not pre loaded. This is ridiculous for the money one pays for these things. I had less backlash with the stock acme screws that came off it.
Any pointers on figuring out the proper thickness of shims?

According to PM they stated
"not one single backlash complaint so far has actually been caused by the ball screw" Which is technically true. I am having issues with the ball nut not the screw.

thanks again

Who knows the thickness, you need to measure it. Start by using a feeler gauge to get a starting point.

Second, while I am not "defending" PM at all, they should be closer in the .001-.002" range, I think your cost/expectations of some one off. A true ground and preloaded ball screw is going to be at least 2 to 3 times "per screw" than you paid for the whole kit.