Steps + Overall turns ratio = Innacurate movement (SOLVED)

[94cobra]

Hey guys, finally got my homebrew CNC Mill all together and have had good luck so far thanks to Acorn, you guys, and plenty of research!

I have the machine up and running, have the limit switches working tied in with the E-stop and have the soft limits all setup.

quick rundown -

pm 30 mill converted with double ball screws
newest acorn cnc
dmm dyn2 servos

DMM recommended 8000 steps per rev. so I used that in the "steps/revolution" boxes in acorn wizard. My ballscrew supplier told me its a 5.08 pitch, so I entered that into the "overall turns ratio" box for each axis. Using .100" increment movements it is continuously adding and extra roughly .002" of actual movement.

So a .100" movement on CNC 12 produces about .102" on my x axis

I have tried combinations of 5.0 and 5.08 for pitch, and 8000 and 8128 for steps per rev, and it is either consistently off -.001 to +.002" per .100" incremental movement.

Not sure what I have to do to get this thing dialed. Do I just keep fudging numbers until I get accurate machine movement? Would I have to do this for each axis individually? Im not feeling great about the inaccurate movement and hope my numbers are not right somewhere.

thank you for any input

[KevinTaylor]

watch this video:
https://www.youtube.com/watch?v=F3SSgb_FnDA

I think around min 35 is what you want

use the attached spreadsheet made by Marty.

[94cobra]

watch this video:
https://www.youtube.com/watch?v=F3SSgb_FnDA

I think around min 35 is what you want

use the attached spreadsheet made by Marty.

thank you for the post, going to watch the video now, It wont let me open your file, it says it is corrupt? is there another location for the spreadsheet?

thanky ou

[KevinTaylor]

viewtopic.php?f=60&t=1085&start=10

[94cobra]

viewtopic.php?f=60&t=1085&start=10

thank you, the spreadsheed is telling me to enter 4.98xxx

because i was experiencing -.001 to +.002 with 5.0 and 5.08 i feel like 4.98 is not goin to work.

But ill give it a go, thank you for the quick response! still watching the video

[94cobra]

Did some more work last night tightened up the gibs and used Marty’s spreadsheet several times...

I think it’s pretty darn close. Thank you centroids forums!!