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TB123 Rev4 Rigid Tapping Setup
Overview
This document describes the theory of rigid tapping parameters to control accuracy of depth of cut and
quality of threads in various working materials
There is no set specification on over travel or und er travel associated with rigid tapping Therefore rigid
tapping must be considered an "art" of machining C entroid makes no warranty or guarantee regarding
rigid tapping depth of over travel
If rigid tapping results are not satisfactory the user should consider purchasing an inexpensive and very
forgiving floating tap attachment or use the very v ersatile thread milling technique both are support ed by
Centroid
Since Rigid Tapping requires the feedback from a sp indle encoder the spindle encoder can also be used
to display the actual spindle speed rather than the commanded spindle speed On the main screen in the
upper right corner directly underneath the feedrate is the spindle speed display If the value of parameter
78 is set to 1 the displayed spindle speed will be the speed seen from the spindle encoder input Fro m
the main screen press F1 Setup >F3 Config >default password is 137 >F3 Params
Graphic representation of parameter controls
Rigid Tapping Parameters
Parameter
Value Function
34 4 096 Spindle Encoder Counts/Revolution
Γ’ Tells the software the encoder counts per
revolution of the spindle encoder Typically the s pindle encoders that have been used in
the past are 1024 line or ppr encoders which produc e an encoder count of 4096 If the
encoder counts up when the spindle turns CW then th e value should be positive If the
encoder counts up when the spindle turns CCW then t he value should be negative
35 5 Spindle Encoder Input or Spindle Axis CNC11
Γ’ In CNC7 and CNC10 this is
designated as the encoder input that the spindle en coder is installed on In CNC11 this
is designated as the spindle axis number The encod er mapping parameters 308 315
tells the software which encoder input the spindle encoder is installed on Please see
charts below
36 Bitwise
value Bit 0 0 Disable rigid tapping 1 Enable rigid tapp
ing
Bit 1 0 Wait for index pulse during rigid tapping 2 Do not wait for index pulse
Bit 2 0 Do not allow spindle override 4 Allow spi ndle override
Example A value of 3 will enable rigid tapping bit 0 = 1 and during execution will not
wait for the index pulse to start bit 1 = 2 and t he spindle override will not change the
spindle speed
bit 2 = 0
Note Please check your operatorΓ’s manual for a detailed description of this parameter
There may be additional bits that are dependent on the software version which are
described in the operatorΓ’s manual
37 3 0 Spindle Deceleration Time
This value is used for setting the spindle decel eration rate
from the programmed spindle speed S down to the s pindle speed of Parameter 68
Check the value of your inverter setting and enter it i e if the inverter is set to 3
seconds deceleration enter 3
68 400
RPM Minimum Rigid Tapping Spindle Speed RPM
This parameter is the speed that the
spindle slows down to from the programmed spindle s peed towards the end of the
tapping cycle The lower the value the more accura tely the Z axis will land on target but
at the expense of possibly stalling the motor which in turn will cause Z to stop short If
this value is too large the off target error increases
69 1 25
sec Duration for Minimum Spindle Speed Mode Seconds
This is a buffer time value to
allow the spindle time to decelerate to the spindle speed defined by parameter 68 If the
number is too small overshoot may occur If itΓ’s t oo large the user waits longer for the
hole to be tapped at the slow speed specified by pa rameter 68
74 4 Spindle M function to be run at the
bottom of the hole for G84 tapping
Spindle M function to be run at the top of the hole to for G74 counter tapping
78 Bitwise
value Bit 0 0 Displayed speed is commanded speed 1 Disp
layed speed is actual speed from
spindle encoder
Bit 1 0 Does not prorate feedrate 2 Prorates prog rammed feedrate proportional to
spindle speed if speed is lower than threshold perc ent set by parameter 149
Bit 2 0 Does not wait for spindle to get up to spe ed 4 Waits for the spindle speed to get
up to speed threshold set by parameter 149 before c ontinuing on with the next line in the
program
84 3 Spindle M function to be run at the
bottom of the hole for G74 tapping
Spindle M function to be run at the top of the hole to for G84 counter tapping
82 720
2 revs
Spindle Drift Adjustment degrees of rotation i e 360 = 1 full rotation 90 = 1/4
rotation This value is the number of turns that the spind le makes to coast to a stop
when it is shut off at the speed specified by param eter 68 This value is proportional to
the distance above the Z target at which the spindle motor must be shut off in order for Z
to land on target Remember that Z is slaved to the spindle speed during rigid tapping
Spindle Encoder Input Chart
CPU7/CPU9 CPU10 B
Encoder Input P35 DC AC
3 2 Encoder Input P35 Encoder Input P35
4 3
5 4 SD3 6
5 4
SD1 21
SD3 drive 6 5
ALLIN1DC/MPU11 OAK
Encoder
Input P35 Encoder
Mapping
Parameter
Encoder Input P35 Encoder
Mapping
Parameter
3 3 P310 = 3 5 5 P312 = 5
4 4 P311 = 4
5 5 P312 = 5 6 6 P313 = 6
6 6 P313 = 6
Graphic Representation of Test Results for Precision
The above chart shows test results of rigid tapping utilizing version 7 14 software The tool used in the
testing was a 1/2 13 spiral fluted tap with TiN coa ting Coolant used was water base soluble oil Hole size
was 0 4218Γ’ Tapping depth was 0 800Γ’ Also note th at the parameters were adjusted to cut air and not
changed for aluminum or cold rolled steel for these tests It can be seen as the material changes so does
the off target values This is due in part to the a mount of torque required from the spindle to cut th e
various types of material For testing purposes th e parameter settings for the above results were as
follows
Parameter 36 = 1 Parameter 37 = 3 Parameter 68 = 100 Parameter 69 = 1 25 Parameter 82 = 108
Summary
Rigid tapping parameters will vary from machine to machine Not all machines are built the same i e
Spindle hp inverter type rigidity etc and tool ing will play a role in performance as well It was found
through our testing that if we changed one physica l parameter i e using a tapping oil instead of water
based coolant it improved the off target values b y 1 5% This is due to the fact that less friction is present
when using special cutting oil therefore requiring less hp by the spindle to drive the tap In most cases
rigid tapping depths should be able to be held with in +/ 0 008Γ’ or less by adjusting parameter 82 for
specific cases
Troubleshooting
Symptoms Possible Problem Solution/Troubleshoot
Rigid tapping was working
and now when running
jobs the message "Option
not available line xx"
appears Demo mode ran out
and permanent
unlocks not entered
From the main screen press
F7 Utility >F8 Options
Verify Tapping Cycles and Rigid Tapping are on
When running a G74 or
G84 rigid tap cycle the
control stops above the
hole to be tapped with a
message in the status
window "moving" and
DOES NOT continue 1 No spindle encoder
feedback
2 No spindle encoder
index pulse
3 On
CPU10 s/n 384
and lower the 6
th axis
index pulse on the
CPU does not work For SD1 only
systems 1 Verify
parameter 35 is set correctly
2 Turn the spindle by hand Check for encoder
movement in PID menu shown in figure 1 If there is nΓ’t
any movement check the spindle encoder the cable
and the connections Figure 2 shows the DB9 pin out for
the encoder
3 Verify the system sees the index pulse from the
spindle encoder
a On a DC system turn the spindle by hand and
look for the asterisk * next to the axis
label that is
designated for the spindle as shown in figure 1
b On an AC system set the bit of parameter 36 to
ignore the index pulse as described above Change t he
value of parameter 35 to 20 and install the spindle
encoder onto the 5
th encoder input on the CPU10 B
Turn the spindle by hand and look for the asterisk *
next to the axis label that is designated for the s pindle as
shown in figure 1
4 If the asterisk is not seen from step 3 then ch eck the
spindle encoder the cable and the connections Fi gure
2 shows the DB9 pin out for the encoder
When running a G74 or
G84 rigid tap cycle you
get a "410 Z axis 3 1 Spindle encoder
turning opposite
direction of spindle 1 Change the sign on the value of
parameter 34 as
described above
2 Try tapping at a reduced spindle speed
position error" motor 2 Spindle speed too
high for tapping
3 Wrong number of
spindle encoder
counts 3 See figure 1 below to verify encoder counts for
the
spindle encoder is set correctly When the spindle is
turned 1 revolution the number of counts should ch ange
by the value thatΓ’s in parameter 34
Tapping does not make it
to the bottom of the hole
Not deep enough 1 Not programmed
deep enough
2 Spindle is turning off
too soon
1 Check Intercon or G code program for depth
2
Parameter 68 69 and/or 82 may need adjusted as
described above
Breaking taps in blind
holes or tapping too deep
1 Programmed too
deep
2 Spindle is turning off
too late
3 Spindle speed is too
high 1 Check Intercon or G code program for depth
2
Parameter 68 69 and/or 82 may need adjusted as
described above
3 Slow down spindle speed
From the main screen press F1 Setup > F3 Config > enter "PASSWORD" > F4 PID to see the PID
menu below
Figure 1 Encoder Input
Figure 2 Spindle Encoder Pin Out
Document History
Rev4 Modified on 2015 04 23 by #270
Rev3 Modified on 2015 04 07 by #270
Rev2 Modified on 2015 03 24 by #270
Rev1 Created on 2001 07 03 by #000