PowerPoint Presentation
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 BasicsUnderstanding True PositionPart 1 :
Grasping the Basics True Position Basics2.000.011.000.01The Part
True Position Basics2.000.011.000.01The Tolerances1.992.010.991.01
True Position Basics1.992.010.991.01The Tolerance ZonePart 1
CenterPart 2 Center True Position Basics1.992.010.991.01The
Question Which Part is Better?Part 1 CenterPart 2 Center True
Position Basics0.991.01Part 1 is within the tolerance zone, butPart
1 Center1.992.01 True Position Basics0.991.01Part 2 is closer to
the Nominal Center and will assemble easier than Part 1Part 2
Center1.992.01 True Position BasicsHow can we set up a tolerance
band that fairly and functionally judges the position of features?
True Position Basics1.992.010.991.01Part 1 CenterPart 2 CenterUse a
Circle instead of a Square! True Position BasicsDefinition
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
BasicsMathematically Speaking.
True Position = X2 + Y2 * 2
X = Difference from Basic X value from Actual X value Y =
Difference from Basic Y value from Actual Y value True Position
Basics2.001.00New Part Print w/True PositionNo Tolerances 0.01 A B
CABCTrue PositionDiametral ZonePrimary, Secondary, Tertiary
DatumsTolerance True Position Basics2.001.00Heres an Example
Calculation 0.01 A B CABC True Position Basics2.001.00CAN WE SHIP
IT? 0.01 A B CABCActual Measurements:X=2.003Y=1.004 True Position
BasicsActual X = 2.003Actual Y=1.004Basic X=2.000Basic Y=1.000 X =
0.003 Y = 0.004 TP = 0.0032+0.0042 * 2or TP = 0.009+0.016 * 2orTP =
0.025 * 2orTP = .005 * 2 so.. True Position Basics True Position =
0.010Hole Center 0.005 from Nominal0.005True Position Result =
0.0100.0030.004Nominal Center at X=2, Y=1 from Basic Dimensions
True Position Basics2.001.00 0.01 A B CABCOur True Position is
within the Specification.Barely! CAN WE SHIP IT?YES, WE CAN! True
Position BasicsLets 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
It Works! True Position Basics2.001.00Same Print, this time a
Real Part 0.01 A B CABC True Position Basics
On a Real Part:
X= 1.9619Y= 1.0081 True Position BasicsActual X = 1.9619Actual Y
= 1.0081Basic X = 2.000Basic Y = 1.000 X = -0.0381 Y = 0.0081 TP =
-0.03812+0.00812 * 2or TP = 0.0015+0.0001 * 2orTP = 0.0016 * 2orTP
= .0390 * 2 so.. True Position Basics True Position = 0.0779Hole
Center 0.0390 from Nominal0.0390True Position Result =
0.07790.03810.0081Nominal Center at X=2, Y=1 from Basic Dimensions
True Position Basics
What??? True Position BasicsExplanation 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 BasicsLets
see how this changes things. True Position Basics
True Position Basics
Watch out for Outliers!
True Position Basics
True Position Basics
Now that we have that sorted out,ONE MORE TIME!
X= 1.9504Y= 1.0104 True Position BasicsActual X = 1.9504Actual Y
= 1.0104Basic X = 2.000Basic Y = 1.000 X = -0.0496 Y = 0.0104 TP =
-0.04962+0.01042 * 2or TP = 0.0025+0.0001 * 2orTP = 0.0026 * 2orTP
= .0507 * 2 so.. True Position Basics True Position = 0.1014Hole
Center 0.0507 from Nominal0.0507True Position Result =
0.10140.04960.0104Nominal Center at X=2, Y=1 from Basic Dimensions
True Position Basics
YES!!! True Position BasicsSo if True Position only gives me
distance from center, how do I know how to make my offsets?ONE MORE
THING..
You might say : True Position Basics
Turn on Additional Position Result in the Characteristic
Settings Editor. True Position BasicsUnderstanding True
PositionYouve got Questions, We have answers.Part 1 : Grasping the
Basics True Position Basics
