Thread definitions in NX5/6

[scotty7]

We have noted that the method for defining a hole with symbolic threads has changed in NX6. It presumably came in at 5, where you directly insert a threaded hole, rather than firstly inserting a hole and then putting a symbolic thread on it. However, looking at the detail, it seems that in the new xml table used by NX for this purpose, the hole dimensions have changed for the tap drill diameter, which changes the actual size of the hole in the model for symbolic threads relative to those produced by NX4.
Why is this the case?

Below is an example for a UNF hole:
NX4
# ----------------------------------------------------------------------------
# Name Major Minor Pitch Tap Drill Shaft Depth
# Dia. Dia. Dia. Dia.
# (internal (external (75% full
# threads) threads) thread)
# (in) (in) (in) (in) (in) (in)
# ----------------------------------------------------------------------------

0-80_UNF 0.0600 0.0451 0.0125 0.0499 0.0568 0.1800

And now the xml for NX6:

<ThreadedHole Standard="Inch UNF" Unit="Inch" Size="#0-80" RadialEngage="0.75" MajorDiameter="0.06" MinorDiameter="0.0451" TapDrillDia="0.0472" Pitch="0.0125" Angle="60" NumStarts="1" Tapered="0" EndCondition="0" Method="CUT" Callout="#0-80 UNF" HoleDepth="0.12" ThreadDepth="0.09" HoleTipAngle="118" ReliefDiameter="0.06" ReliefDepth="0.03" ReliefTipAngle="118" ReliefChamferAngle="45" ReliefChamferOffset="0.005" StartChamferDiameter="0.06" StartChamferAngle="45" EndChamferDiameter="0.06" EndChamferAngle="45" ThreadForm="UNF"/>

 

[JohnRBaker]

I will admit it, I'm PERSONALLY responsible for the original pre-NX 5.0 thread standards table. At the time that this feature was implemented we didn't have a lot of time to research it and since we started out with a very limited set of data, the decision was made to use a nominal 'rule-of-thumb' where the pilot drill was set to be 75% of the maximum-diameter of the thread.

When we decided to implement a true threaded-hole feature in NX 5.0 we decided to spend the time and work out something that was based on actual manufacturing practices rather than use a simple ratio for the pilot hole size. Besides, we were adding so many additional standards it was decided that we should do what was right rather than base it one what was done in the past, despite that fact that it had served us well (although not without a few complaints about the arbitrary nature of the approach I took) for well over 10 years or so.

Anyway, I think we all agree that since there are established standards in this area that we should follow them rather than the expedient route I took originally.

John R. Baker, P.E.
Product 'Evangelist'
Product Design Solutions
Siemens PLM Software Inc.
Industry Sector
Cypress, CA

http://www.siemens.com/plm

http://www.plmworld.org/museum/

To an Engineer, the glass is twice as big as it needs to be.