Sketch in Drafting

[phillpd]

NX 6.0.5.3

On the drawing sheet, I create 2 vertical lines. I then create a horizontal dimension between those lines, selecting the mid-point of each.

Why the warning ... "Some of the selected objects or snap options are not allowed for driving dimensions" ? What's the issue with selecting the mid-points ?

Specialty Engineered Automation (SEA)

http://www.sea4ug.com

a Siemens PLM Solutions Partner

 

[JohnRBaker]

First you have to understand that when it comes to linear dimensions, what's actually being dimensioned are 'points'.

And when if comes to curves, they are all defined by 'points', some are obvious and some are not. In the case of a Line, it's the start & end points. An Arc, the center point and the start & end points (even if it's a full circle). A Spline, the knot points. An Ellipse, the center point and the start & ends points (same as an arc/circle). A Conic, the start & end point as well as the control point. In each case, the common DEFINING characteristic was a 'point'.

Therefore when it comes to creating DRIVING dimensions, you can only select a DEFINING point. With 'reference' dimensions (which are still associative, just not driving), in addition to DEFINING points, they can also reference the so-called 'snap points'. Now if a snap point turns out to also be a DEFINING point, such as End Points, or an Arc Center, or a Knot (control) Point, then dimensions which reference them can also be DRIVING dimensions. Generally speaking however, Snap Points such as Mid-Point, Intersection Point, Point on Curve, Point on Face, Quadrant Point and some Control Points, can never be DEFINING points and therefore cannot be referenced by DRIVING dimensions.

Anyway, I hope this clears-up a few things and that it helped you understand better what's happening when you're Sketching on the face of a Drawing.

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.