General CNC Chat > Building or Buying a Wood routing table.. Beginnners guide..

inconsistency in Z axis

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noob64:
Home built Wood CNC

I just installed a 8mm acme rod on my Z axis and I am trying to set it up.
I don't have an anti backlash nut, not sure if this is my issue.
Nema 23 motor.

I have mounted a digital caliper to the carriage to measure my movement for set up.

I am measuring a 50mm distance using Z50 and Z0 for the movement and then measuring the distance and resetting each time.

Here are my measurements in mm:

up   -.2
down   +.36
up   +.18
down    -.01
up   +.32
down   +.24
up   +.07
down   +.35
 
I've done more cycles, but this illustrates my perceived problem

up off by ave.1925 range of +.32 to -.2
down off by ave.24 range of +.24 to -.01

both averages are less than ten thousandths.

Is this too great and inconsistency? What are acceptable tolerances for the different axis' in wood and hopefully aluminum at some point?

thanks, Mike

ger21:
Acceptable tolerances are whatever you find acceptable.
Having said that, you should be getting more consistent results.
Is everything tight mechanically?

noob64:
I ground a flat on the acme rod and added another set screw to contact the flat, so I think so. What is the standard repeated precision that I shoot strive for?

ger21:
What's keeping the acme screw in position? If it's supported by the motor, then you won't get any better, as the motor shaft will have some end play from the bearings.

noob64:
I used a pillow block. See if anything i the attached picture jumps out at you. I do have another motor I can try

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