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TB037 Rev2 Measuring Backlash
Overview
This document describes the steps required to correctly measure backlash in a machine It further explains how to check and/or correct
these values in the parameter settings of a Centroid CNC Control
Prerequisite
You must verify your revs/inch ratios are set up properly If they appear to be incorrect or if you are not sure refer to
TB036 Measuring Motor revs/inch before measuring backlash
Required Tool 001" dial indicator with a 1" travel plunger and adjustable magnetic stand
Setup steps
1 From the main screen in the CNC10 software press the following keys in order to get into the following parameter screen F1
Setup
F3 Config
enter the password 137
press enter F2 Machine
and then F2 Motor
2 Enter the present values into the chart below for Lash Comp
Present Value Before Lash Comp Measured Value After Lash Comp
XĆĀ ĆĀ ĆĀ ĆĀ ĆĀ ĆĀ ĆĀ XĆĀ ĆĀ ĆĀ ĆĀ ĆĀ ĆĀ ĆĀ
YĆĀ ĆĀ ĆĀ ĆĀ ĆĀ ĆĀ ĆĀ YĆĀ ĆĀ ĆĀ ĆĀ ĆĀ ĆĀ ĆĀ
ZĆĀ ĆĀ ĆĀ ĆĀ ĆĀ ĆĀ ĆĀ ZĆĀ ĆĀ ĆĀ ĆĀ ĆĀ ĆĀ ĆĀ
WĆĀ ĆĀ ĆĀ ĆĀ ĆĀ ĆĀ ĆĀ WĆĀ ĆĀ ĆĀ ĆĀ ĆĀ ĆĀ ĆĀ
3 From the F2 Motor
screen use the arrow keys to change the values of Lash Comp to zero 0 0000 then press F10 Save
to save
these values
Measuring Backlash before 2 6x software The example below will be for the X axis
1 Extend the Quill a few inches
2 Set up the dial indicator parallel to the X axis and perpendicular to the Z axis such that the plunger will come in contact with the quill
Be sure the quill is free from chips and grease See diagram 1
3 Slow jog the X axis until the quill just touches the plunger on the dial indicator and then stop
4 Switch to Incremental Jog mode and set the increment to 01" Note If parameter 40 is set to 0 001 use the x10 key however if P40
is set to 0 0001 use the x100 key
5 Continue jogging the X axis moving the plunger incrementally toward the quill three 3 times Observe and record the dial indicator
start position DO NOT TOUCH THE DIAL INDICATOR or the stand
6 Continue to jog the X axis moving the plunger incrementally toward the quill ten 10 times
7 Jog the X axis IN THE OPPOSITE DIRECTION ten 10 times Observe and record the dial indicator finish reading With no
mechanical backlash the start and finish values will be the same position Subtract Finish Start = Lash Repeat steps 3 to 7 to verify
Lash before entering value
8 Enter the Lash comp value for the X axis and save your changes Repeat this procedure for all axes
Measuring Backlash after 2 6x software PC based backlash
1 Extend the Quill a few inches
2 Set up the dial indicator parallel to the X axis and perpendicular to the Z axis such that the plunger will come in contact with the quill
Be sure the quill is free from chips and grease See diagram 1
3 Slow jog the X axis until the quill just touches the plunger on the dial indicator and then stop
4 Switch to Incremental Jog mode and set the increment to 01" Note If parameter 40 is set to 0 001 use the x10 key however if P40
is set to 0 0001 use the x100 key
5 Continue jogging the X axis moving the plunger incrementally toward the quill three 3 times Observe and record the dial indicator
start position DO NOT TOUCH THE DIAL INDICATOR or the stand ĆĀ
6 This is where it changes PC based backlash has no effect on jogging ĆĀ So at this point press F1 Setup
F1 Part
set it to the axis you
are measuring backlash on and press F10 Accept
7 Press ESC
to get back to the main menu then press F3 MDI
and command a move toward the quill i e X 0 1 F12 press cycle start
ĆĀ Then command a move back to zero i e X0 F12 press cycle start
ĆĀ Make sure you specify the feedrate of 12ipm to get the best
possible readings ĆĀ Observe and record the dial indicator finish reading With no mechanical backlash the start and finish values will be
the same position Subtract Finish Start = Lash Repeat step 7 to verify Lash before entering value ĆĀ With backlash value entered
check again to verify that the indicator comes back to zero
8 Repeat the procedure for all axes
ĆĀ
Notes
Measure the backlash several times until you achieve the same result several times
Measure backlash where the machine is to be operating the most usually the center of travels If the jobs that are being
run use most of the travel envelope measurements can be averaged
If you measure more than 0015" of lash the machine should be mechanically adjusted or repaired Although the control
will attempt to compensate for excessive lash > 0015" it cannot completely eliminate the underlying mechanical problems
that result in unsatisfactory performance
Document History
Rev2 Created on 2010 04 16
by #240
Rev1 Created on 1999 09 09
by #000