Last updated: November 28, 2001


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After attempting to teach the use of True Position including RFS, MMC & LMC of shaft and bores based upon ASME GD&T Y14.5-1994, I found my self continuously re-explaining it to those who tried to use it properly.

So, to end my peril, I decided to write a Visual Basic program to handle the function of using true position showing the bonus tolerance and using it in the calculations.

I continuously add features to this program as I think of them.  The software is currently being updated to include the measurement of 60 threads.

Below are screen shots of the program.  Please email me with inquiries regarding the software.  It is available for purchase.

The GD&T interface requires no knowledge of the formula's behind the application of GD&T.  The only two sets of data must be know.  One, the specifications of the hole/shaft must be know.  Secondly, the actual location must be known.

True position is calculated by the user first selecting what type of modifier is applied to the true position callout.  Modifiers are either RFS (regardless of feature size), MMC (Maximum Material Condition), or LMC (Least Material Condition).  Each is denoted by a symbol found with in the feature control frame.

Maximum Material Condition
Least Material Condition
Regardless of Feature Size (Latest revision of Y14.5 uses the omission of this symbol to denote RFS)
Feature Control Frame

Secondly, the specification and actual location data is entered in the interface.  Once all required information has been entered, you need only click the calculate button and the software will display the actual true position, the amount of bonus tolerance (if any) and the tolerance with including the bonus tolerance.  If the actual true position is beyond the total tolerance, it appears in red font.

Lastly, I have had occurrences of needing to quickly know the true position of a hole centered in a shaft, or two concentric diameters on the same shaft, etc.  If the shaft is place on "V" block and an indicator is placed in the center of centered hole, the hole can be examined for pass/fail against the specification true position by measuring & reading the TIR.  If the TIR does not exceed the TIR calculated from the software, the hole is within the true position tolerance.  NOTE: This will only determine if the hole is within specification.  It will not give an value in true position terms.

Additionally, right angles are solved quickly and easily via the interface above.  With the interface below you can forget manual trigonometric calculations.  As long as two values (one side & one angle, two sides, or two angles) are known, the software will solve for the remaining sides.

Every need to calculate the angle of a tapered shaft/bore?  With the interface below you can forget manual trigonometric calculations.