OK, the 'slider' is used to set the value of the ratio of 'd/t', where 'd'=distance and 't'=thickness:
So for example, if you set the slider to '1.0' and based on the size of the 'bend' versus the thickness of the section, the value of 'd' was larger than 't', the result would look like:
That is, the 'surface pair' representing the two curved surfaces would be INCLUDED.
However, if the value of 'd' was smaller than 't', then it would look like the first image above, but only if the 'Advanced Creation and Trimming' option were toggled OFF. If it were toggled ON then you would get this result:
Basically what the 'd/t' ratio, as set by the slider, controls is whether, and for what size, will the faces of 'bends' or other small 'features' be included as 'face pairs' or not when computing the Midsurface. I hope that helps.
Note that for NX 7.5 we're completely reimplemented the Midsurface function provide more explicit control over which 'surface pairs' are to be included and we therefore no longer use this 'd/t' ratio scheme.
As for the issue of the multiple features, in essense, what a midsurface feature is, is a 'feature group' which is made up of individual 'face pair' features (BTW, this behavior has NOT changed in NX 7.5). That's why when you select the Midsurface feature in the Part Navigator, the relevant 'face pair' features are also selected. Note that this scheme does allow you to 'delete' one or more of the pairs and the Midsurface feature will update accordingly. Again I hope this helps clear things up.
John R. Baker, P.E.
Product 'Evangelist'
Product Design Solutions
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
