5 Axis Knuckle Type Alignment and Concentricity
2014
Introduction _________________________________________________________________ 2
Initial Setup__________________________________________________________________ 2
Alignments __________________________________________________________________ 3
C Axis Plane Parallel to XY plane ______________________________________________________ 3
C Axis Straightness _________________________________________________________________ 4
B Axis Straightness _________________________________________________________________ 6
Spindle Centerline to B Axis Centerline _________________________________________________ 7
Concentricity______________________________________________________________________ 9
Pivot distance ____________________________________________________________________ 10
Finalization of TCP offsets __________________________________________________________ 13
1
Introduction
An initial verification of the linear axis, and relative planes should be confirmed with a laser. If
XY,YZ, and XZ are not square and perpendicular to each other, then the following steps may or
may not hide an underlying issue. If there is a linear misalignment the knuckle alignment can be
made to look correct in one XYZ position on the machine but be incorrect in another. The
following steps, measurements and compensations, must be performed in the order listed.
Deviation in this will cause inaccurate measurements to be recorded and compensated.
Initial Setup
Tools needed:
1. Ground Tool Shaft with Tool Holder ( provided by CMS ) All of these tests described below
will have this tool in the spindle.
Fig 1.1: Ground Shaft
It is important to know the real length of this tool from setting plane to the end of the ground
shaft. Also near the end of the shaft we want to place a mark with a fine marker around the
circumference of the shaft. A course measurement from the setting plane to this mark will need
to be placed in H97. The reason for this mark is so we can be visually sure we are making some
measurements at the same location.
2. Dial indicator and magnetic base preferably Metric ( 2 would be best )
Fig 1.2: Dial indicator
3. Allen Wrenches and Shim Stock
Fig:1.3: Allen wrench
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Alignments
C Axis Plane Parallel to XY plane
The first step is to make sure the C axis plane is parallel with the XY plane. This is checked by
placing the B axis at 90 degrees and C at 0. Then place the indicator under the ground shaft
pointing up. Jog as you need to place the mark that was made near the end of the shaft, do not
move Z axis in any way. Find the high point of the shaft and zero the indicator. Rotate C to 90 ,
180, 270. At each quadrant come back over the indicator at the mark placed and find the high
spot. Generally you should not see more then 0.02mm at this kind of distance. See pictures.
Fig 1.4: Position B90 C0
Fig: 1.6: Position B90 C180
Fig 1.5: Position B90 C90
Fig: 1.7: Position B90 C270
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To correct a misalignment a shim must be placed as needed in between the Z mast and the
mounting plate for the C axis gear box. If a shim is used, everything must be tightened and
rechecked until this passes the 0.02mm measurement.
C Axis Straightness
Place the B axis at 90 Degrees and C at 0. Then with the indicator/needle pointed horizontally
(reading dial on top view) at the mark on the ground shaft, find the high spot, and zero the
indicator. Raise the Z axis to clear and rotate B to 0 verify and then to B-90. Jogging X and Z
get back to the mark and the high spot; do not move the Y axis. This will give a large distance
to verify C straightness. Jog the C small amounts if you see error. In order to adjust and reduce
the error move the C axis half of what you see the error from B90 to B-90.
For example if the difference in errors is 0.1 in the readings adjust the value to 0.05 (0.1/2) and
verify. Repeat test and adjustment in small increments in either the positive or negative side till
indicator reads 0 in both B90 and B-90. The distance the C has been jogged to get a zero reading
should be recorded and added or subtracted from the value of parameter 1240 C axis. Every
single time this parameter is changed the machine needs to be shut down and restarted. Once
doing this, reference the machine, and re-verify the test. You will either be correct or off double
what you originally were. If this is the case do the opposite of adding or subtracting to the
original value of 1240.
NOTE: ALWAYS SHUTDOWN AND RESTART THE MACHINE AFTER CHANGING
PARAMETER 1240
Fig 1.8: Position B90 C0
Fig 1.9: Position B-90 C0 (B PLANE)
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B Plane
Check 2
Point 3
Check 3
Point 2
Fig 2.0: Position B0 C0
Check 1
Point 1
Fig 2.1: Check points
Note: This test is done to check if the C axis is perpendicular to the B axis. The test done for
B90C0 and B-90C0 (Check 1 and Check 3 in Fig 2.1) verifies the first two points on the B plane
as shown in Fig 1.8 and 1.9.
We check for B plane parallel to XZ plane using the point 3(Check 2 in Fig 2.1) This test is
quick as we have verified 2 points of this plane in the step above, jogging the Z axis to clear,
command the B to 0 as shown in Fig 2.0. Jog the X and Z to get the indicator back to the mark
on the ground shaft. Do not move the Y axis. If the B plane is true this point will also read 0 on
the indicator. As with the C axis plane a measurement of 0.02mm or less is ok.
Note: A larger value will require a physical adjustment with shims. On most machines this is a
ground assembly and will not require a physical intervention. If a large enough crash has taken
place a shim can be placed below the C axis gear box, where the knuckle mounts to the gear box.
If this is done you must start back at Step 1.
Thus every single one of the three points we touch make up parts of the B plane.
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B Axis Straightness
With B and C at 0, place the magnetic base of the indicator on the ground shaft. Stretch the
indicator to its farthest point. Make sure the indicator is pointing down and is the lowest point
on the head. Jog the Z down to the table. Don’t be afraid to “load up” the indicator. We want
some load there to keep the indicator in one spot. Zero the indicator. Then with the hand wheel
turn on “INCLINED PLANE”. Jog the C axis near or to 180 degrees. If the B axis is not
straight you will see a shift in the indicator at the points (“Potato chip phenomenon”). Jog the B
small amounts if you see error. Generally speaking move the B axis half of what you see the
error from C0 to C180. Repeat test by rotating C axis and adjusting B by small amounts till
indicator reads 0 in both C0 and C180. The distance the B has been jogged to get a zero reading
should be recorded and added or subtracted from the value of parameter 1240 B axes. (Similar to
what you would do in the C straightness test to adjust error). A change in this parameter will
require the machine to power down and back up. Once doing this, reference the machine, and reverify the test. You will either be correct or off double what you originally were. If this is the
case do the opposite of adding or subtracting to the original value of 1240.
ALWAYS SHUTDOWN AND RESTART THE MACHINE AFTER CHANGING
PARAMETER 1240
Fig 2.2: B0C0
Fig 2.3: B0C180(C INCLINE PLANE)
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Spindle Centerline to B Axis Centerline
B CENTER PROGRAM
<B-SPIND>
G92.1X0Y0Z0B0C0
G92X0Y0Z0
F1000
G43.4H97
G91G01
Z100
G90
B0
G49H0
M00
G43.4H97
G01G90B90
G91Z-100
G00
M00
G91G01Z100
G90B-90
G91Z-100
G00
M00
G01
G91Z100
G90B90
G91Z-100
M30
%
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This test requires a program. Use the program above. Command the B to 90 and C to 0. Place
indicator and machine just like the first picture in Step 1, find the high spot on the shaft like
before as well and zero the indicator. Once it is zeroed out measure the length of the tool.
Note: While measuring the tool measure up to the mark that is made on the tool
Change the value of H97 by entering length of the tool in offset. Run the program which is
shown above. The program is basically incremental from your start point. TCP( Tool center
point) will turn on, bring the head vertical, turn the TCP off then back on and come back down
to the indicator. Make sure it still reads Zero. Press cycle start again and it will flip over to the
other side and come back down on the indicator. Make note of the value. Press cycle start. It will
then flip back over to the beginning position. Watch the head when it flips over to B-90 verify
that this changed the position in Z only and did not instead slide the head front to back.
If you notice a shift in the position of the indicator then, go to Parameter 19710. (Some
machines depending on the orientation of the axis the correct parameter may be 19709. If you
have a question which is right, put a large value in one field and run program. Check if the
machine corrects in Z or moves in X or Y. We want the machine to move in Z. Adjust the tool
offset by taking half the value of error on the indicator dial and adding it to the initial value in the
tool offset. Rerun the program. If the correct value is 19709 then substitute that in this document
from this point forward.) Add or subtract as needed to 19710 till the program runs and both B90
and B-90 read 0.
Note: This parameter change does not require a power cycle of the control.
Fig 2.4: Positions of tool on indicator
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Concentricity
With the B and C at 0, place two indicators pointing horizontally at the ground shaft 90 degrees
to each other and Zero them. If you only have one indicator you will have to move it parallel to
Y and parallel to X as you check each position. In MDI turn on G43.4 (TCP) then command the
C to 180. Do not use inclined plane and the hand wheel. The machine interpolation is not as
exact as a straight command from MDI. Take note of the indicator that has moved the most. You
want to correct that one first. If the indicator shifts and shows the error then the parameters we
need to adjust for this are 19712 for the X (Change Tool2/1offset X) and 19713 (Change
Tool2/1offset Y) for the Y. Return the C to 0 in MDI press reset and adjust the correct parameter
by half of what you saw the dial indicator move just like the previous tests. Do this until you can
go from C0 to C180 with the indicator not moving in the X or Y direction.
Use of TCP: The purpose of all machine tools is to move the tool in a programmed path, which
is defined as a series of positions. For the part, a position is the position of the Tool Center Point
(TCP). If the finished part is programmed, we need to transform the coordinates of the TCP to
the actual machine axes. These calculations are based on the programmed positions and the tool
dimensions. For 5-axis machine, TCP has 3 position-axes (XYZ) plus 2 orientation-axes (BC).
The position axes locate the tool tip while the orientation axes set its orientation. Jogging in TCP
mode is a lot easier than moving each axis separately, since we control the position and
orientation of the tool, not the machine
Fig 2.5: Concentricity: Parallel to X axis
Fig 2.6: Concentricity test: Parallel to Y axis
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Pivot distance
B
Fig 2.7: Pivot distance
The perfect orientation mechanism will change the tool orientation without changing its location.
In such a case changing orientation doesn't require any linear move. This is impossible to
achieve because of mechanical constrains. For B tilt there is a certain distance between the center
of rotation (pivot) and the tool tip. This is called pivot length/distance. In some machines it is
reduced to a small distance by a clever design. However, tool length changes this length and
therefore tool length setting must be accurate.
Setup: Place the B axis at 90 Degrees and C at 0. Then with the indicator pointed horizontally at
the ground shaft, find the high spot, and zero the indicator. Make note of the Z axis display.
Write this down. Jog the Z axis up and turn the B to 0. Bring the head over and jog the Z down
till the indicator reads zero. Make note of the Z axes display for each position from machine
value. (Do not use absolute or relative readings of Z)
Fig 2.8: B0 C0
Fig 2.9: B90 C0
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Note: If you are using a ball indicator then measure the length of the tool and from its full length
subtract the radius and enter that as the offset value.
Now for the best part, the math part! ^_^
For B0 C0
𝑍𝐿 = 𝑍𝑚𝑎𝑐ℎ𝑖𝑛𝑒 𝑣𝑎𝑙𝑢𝑒 − 𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡ℎ𝑒 𝑡𝑜𝑜𝑙
For B90 C0
𝑍𝑅 = 𝑍𝑚𝑎𝑐ℎ𝑖𝑛𝑒 𝑣𝑎𝑙𝑢𝑒 − 𝑅𝑎𝑑𝑖𝑢𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑡𝑜𝑜𝑙
Pivot distance = 𝑍𝐿 − 𝑍𝑅
Note: Pivot distance is always a positive number because it is a value of length. (The length
of any object can never be a negative number)
Math functions for calculating the readings:
Simple to remember: Like signs we add, unlike signs we subtract but for the final result place the
sign of the number with the higher value
(+) * (+) = (+)
(-) * (-) = (+)
(+) * (-) = (-)
(-) * (+) = (-)
Here is an example:
Radius of tool = 10mm
Length of tool = 100mm
For B0 C0 note the Z value of machine reading:
If 𝑍𝑚𝑎𝑐ℎ𝑖𝑛𝑒 𝑣𝑎𝑙𝑢𝑒 = −200 and length of the tool = 100mm
Then from formula above plug in the values:
𝑍𝐿 = 𝑍𝑚𝑎𝑐ℎ𝑖𝑛𝑒 𝑣𝑎𝑙𝑢𝑒 − 𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡ℎ𝑒 𝑡𝑜𝑜𝑙
𝑍𝐿 = −200 − 100 (same signs we add but use the sign of the higher value which is negative
200)
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𝑍𝐿 = −300
For B90 C0 note the Z value of machine reading:
𝑍𝑅 = 𝑍𝑚𝑎𝑐ℎ𝑖𝑛𝑒 𝑣𝑎𝑙𝑢𝑒 − 𝑅𝑎𝑑𝑖𝑢𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑡𝑜𝑜𝑙
If 𝑍𝑚𝑎𝑐ℎ𝑖𝑛𝑒 𝑣𝑎𝑙𝑢𝑒 = −400 and radius of the tool = 10 mm
Then from formula above plug in the values:
𝑍𝑅 = 𝑍𝑚𝑎𝑐ℎ𝑖𝑛𝑒 𝑣𝑎𝑙𝑢𝑒 − 𝑅𝑎𝑑𝑖𝑢𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑡𝑜𝑜𝑙
𝑍𝑅 = −400 − 10
𝑍𝑅 = −410
(Same thing like signs we add and place the sign of the one with the higher value which is
negative 400)
FINAL FORMULA
Pivot distance = 𝑍𝐿 − 𝑍𝑅
Pivot distance = -300 – (-410)
Pivot distance = - 300 + 410 (Remember math function (-) * (-) = (+) )
Pivot distance= 110 (The distance is always positive no matter what the end result is)
Check parameter 19709 for the values and add the inverse of it to the pivot distance. The value
obtained needs to be checked with the value in 19666 and changed there.
For example:
If Pivot distance = 110
Check for value on parameter 19709: If reading = - 0.075
Then,
1. Take the inverse(opposite sign) = + 0.075
2. Then add it to pivot distance: 110 + 0.075 = 110.075. Write this value down.
3. Go to parameter 19666 and enter the value that is calculated as in step 2.
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Finalization of TCP offsets
Some newer machines may not have 19667 filled out if this is the case do not worry about this
step then. Specifically is 19665 bit 4 is zero. (Check for SPR value and if it is equal to 0 then
there is no need for finalization of TCP offset)
Now that all the movement parameters are filled out at this point the control needs to comp these
values back out of the control for XYZ positioning. This is so the XYZ value of G43 and G43.4
are equal to each other. G359 takes the active offset and sends it to the hand wheel.
Check parameter 19709 for the values and add the inverse of it to the pivot distance. The value
obtained needs to be checked with the value in 19666 and changed there.
Below are two sets of examples in case some people have had to use 19709 rather than 19710
EXAMPLE 1:
19710 is a Y value Example number = -0.075
19712 is a X value Example number = 140.45
19713 is a Y value Example number = 0.08
19666 is a Z value = 110
Take 19710 and 19713 add them together = 0.005
In parameter 19667 place the invers of 19712 in X
In parameter 19667 place the invers of the result of 19710 and 19713 in Y
In parameter 19667 place the invers of 19666 in Z
So 19667 should look like
X -140.45
Y-0.005
Z-110
EXAMPLE 2:
19709 is a X value Example number = -0.075
19712 is a X value Example number = 0.08
19713 is a Y value Example number = 140.45
19666 is a Z value = 110
Take 19709 and 19712 add them together = 0.005
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In parameter 19667 place the invers of the result of 19709 and 19712 in X
In parameter 19667 place the invers of 19713 in Y
In parameter 19667 place the invers of 19666 in Z
So 19667 should look like
X-0.005
Y -140.45
Z-110
______________________________________________________________________________
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