Transcript True Position Basics - Ellison Technologies

True
Position
Basics
NOTICE :
This presentation was given at the October 2007
“Lunch N Learn” at J&H Machine Tools in
Charlotte.
The presentation is meant to be viewed with the
narration and detailed explanation of the presenter.
True
Position
Basics
Understanding True
Position
Part 1 : Grasping the “Basics”
True
1.00±0.01
2.00±0.01
The Part
Position
Basics
True
1.99
Position
Basics
2.01
1.01
0.99
1.00±0.01
2.00±0.01
The Tolerances
True
Position
Basics
1.01
Part 1 Center
Part 2 Center
0.99
1.99
The Tolerance Zone
2.01
True
Position
Basics
1.01
Part 1 Center
Part 2 Center
0.99
1.99
2.01
The Question… Which Part is Better?
True
Position
Basics
1.01
Part 1 Center
0.99
1.99
2.01
Part 1 is within the tolerance zone,
but…
True
Position
Basics
1.01
Part 2 Center
0.99
1.99
2.01
Part 2 is closer to the Nominal Center and will
assemble easier than Part 1
True
Position
Basics
How can we set up a tolerance band that
fairly and functionally judges the position
of features?
True
Position
Basics
1.99
2.01
1.01
Part 1 Center
Part 2 Center
Use a Circle instead of a Square!
0.99
True
Position
Basics
Definition Time!!!
The result of a True Position Characteristic is the
diameter of a circle, centered on the basic
dimensions from the specified datums, that
contains the actual center point.
True
Position
Basics
Mathematically Speaking….
True Position =
ΔX2 + ΔY2
*2
ΔX = Difference from Basic X value from Actual X value
ΔY = Difference from Basic Y value from Actual Y value
True
Position
Basics
True Position
Diametral Zone
Tolerance
Ø 0.01 A B C
No Tolerances
Primary,
Secondary,
Tertiary Datums
A
1.00
2.00
B
C
New Part Print w/True Position
True
Position
Basics
Ø 0.01 A B C
A
1.00
2.00
B
C
Here’s an Example Calculation
True
Position
Basics
Ø 0.01 A B C
A
Actual
Measurements
:
1.00
X=2.003
2.00
B
C
CAN WE SHIP IT?
Y=1.004
True
Actual X = 2.003
Basic X=2.000
Position
Basics
Actual Y=1.004
Basic Y=1.000
Δ X = 0.003
Δ Y = 0.004
TP = 0.0032+0.0042
*2
or
TP = 0.009+0.016
*2
or
TP =
or
TP =
0.025 * 2
.005 * 2
so…..
True
True Position
True Position
Result = 0.010
Nominal Center at
X=2, Y=1 from Basic
Dimensions
Position
Basics
=
0.010
Hole Center
0.005 from
Nominal
True
Position
Basics
Ø 0.01 A B C
Our True
Position is
within the
Specification….
A
1.00
Barely!
2.00
B
C
CAN
YES, WE SHIP
CAN!IT?
True
Position
Basics
Let’s do this very example in
Calypso and see if the math
works out!
True
Position
Basics
True
Position
Basics
This is a Theoretical
feature with X Y
coordinates placed
exactly at 2.003 and
1.004.
True
Position
Basics
True
Position
Basics
Ø 0.01 A B C
A
1.00
2.00
B
C
Same Print, this time a “Real” Part
True
Position
Basics
On a “Real” Part:
X= 1.9619
Y= 1.0081
True
Position
Basics
Actual X = 1.9619
Actual Y = 1.0081
Basic X = 2.000
Basic Y = 1.000
Δ X = -0.0381
Δ Y = 0.0081
TP = -0.03812+0.00812
*2
TP = 0.0015+0.0001 * 2
or
TP =
0.0016
or
TP =
.0390 * 2
*2
so…..
or
True
True Position
Position
Basics
=
0.0779
Hole Center
0.0390 from
Nominal
Nominal Center at
X=2, Y=1 from Basic
Dimensions
True Position
Result = 0.0779
True
Position
Basics
True
Position
Basics
Explanation Time!!!
The GD&T standard specifies that the
FUNCTIONAL center be used for
calculations. This means for a hole,
that the Maximum Inscribed fit be
used. Calypso does this automatically!
True
Position
Basics
Let’s see how this changes
things.
True
Position
Basics
True
Watch out for
Outliers!
Position
Basics
True
Position
Basics
True
Position
Basics
Now that we have
that sorted out,
ONE MORE TIME!
X= 1.9504
Y= 1.0104
True
Position
Basics
Actual X = 1.9504
Actual Y = 1.0104
Basic X = 2.000
Basic Y = 1.000
Δ X = -0.0496
Δ Y = 0.0104
TP = -0.04962+0.01042
*2
TP = 0.0025+0.0001 * 2
or
TP =
0.0026
or
TP =
.0507 * 2
*2
so…..
or
True
True Position
Position
Basics
=
0.1014
Hole Center
0.0507 from
Nominal
Nominal Center at
X=2, Y=1 from Basic
Dimensions
True Position
Result = 0.1014
True
Position
Basics
True
Position
Basics
ONE MORE THING…..
You might say :
“So if True Position only gives me distance from center,
how do I know how to make my offsets?”
True
Turn on Additional Position
Result in the Characteristic
Settings Editor.
Position
Basics
True
Position
Basics
You’ve got Questions, We have answers.
Understanding True
Position
Part 1 : Grasping the “Basics”