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Author Topic: Movement of Z axis is great in down direction but is incorrect in Up direction  (Read 2213 times)

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Offline CES

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Hi Everyone,

  Search is broken as are external links into the database so I'm posting this thread.

I noticed that my Grizzly Mini Mill X axis was a little off in -X and +X. So I decided to re-calibrate the Mill. Z axis gives -.01 inch over .1 inch in Up direction but is almost spot on in down direction. I can't find a setting for forward versus reverse movement in Mach3.

Can anyone drive me in the correct direction?

Thanks,
CES
Hi,
there is no 'steps per unit' in one direction and 'steps per unit' in the other direction.

If it takes 1000 steps to travel 1 inch upwards it will take 1000 step to travel 1 inch downwards.

What you have described is either backlash and/or missing steps.

If it is backlash the error will not accumulate but it will if you are missing steps. This suggests a test that you can make
to determine which.

MDI:
G0 Z1
Z0
Z1
Z0
Z1
Z0
Z1
Z0
Z1
Z0

This just rapids the Z axis up one inch and then down one inch. If you have backlash then the start and end point could well be different
to each other by the amount of backlash. If your missing steps the error will accumulate with each iteration of the cycle.

Report back with your results.

Craig
My wife left with my best friend...
     and I miss him!

Offline CES

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Thanks JoeAverage,
  Thats what I was doing except 0.1 inch, so:
G1 G91 Z-0.1
Z0.1
Z-0.1
Z0.1
Z-0.1
The movements in negative direction are spot on but positive direction is off. Rather then 0.1, I get 0.097
So DRO's read:
-0.100
0.003 Reset to 0.000
-0.1
0.003, Reset to 0.000
...
I checked backlash, it is close to 0.0008 (about as close as I can get it to 0.0005 which is the accuracy of the dial indicator.
I'll check again but thanks for the reply.
Hi,
try moving further, 1 inch is my suggestion.

Do not reset between cycles and you want at least ten cycles. THEN compare the beginning and end points.

Craig
My wife left with my best friend...
     and I miss him!
Hi,
additionally I notice you are using incremental moves. What is your step per unit vale for the Z axis?

Craig
My wife left with my best friend...
     and I miss him!

Offline CES

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Min step is 0.0001 from motor to bed/head.

Offline TPS

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sounds like a Resolution/rounding Problem.

pls post a Screenshot of your

Config -> Motor Tuning -> Z-AXIS MOTOR MOVEMENT PROFILE Screen
anything is possible, just try to do it.
if you find some mistakes, in my bad bavarian english,they are yours.

Offline RICH

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Suggest you post a picture which shows  the Z axis.

RICH

Offline CES

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The settings are as follows:
Steps per: 10000
Velocity (inch): 15
Acceleration (inch): 19
Step Pulse: 2
Direction Pulse: 1
G's result is 0.0492136

This gives me 1 axis motor movement. That is I push the Page Down button ones and I get the motor movement for 1 increment

Offline TPS

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hello CES,

you have to tell us more about your installion (Motor , Motor Connection, Gear, Belt driven, drirectly driven by Ball screw),
because you data for the Z-axis are very strange.

steps per:10000 ?? are you running a servo Motor on z-axis?
velocity 15inch/min ok i have to calculate (15x25.4 = 381mm/min, i am in metric) that is nothing

this data "seems" to be a Little bit "strange".

TPS
anything is possible, just try to do it.
if you find some mistakes, in my bad bavarian english,they are yours.