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NX12 Mfg mult-axis milling : Variable Contour Surface Area & grid errors

NX12 Mfg mult-axis milling : Variable Contour Surface Area & grid errors

NX12 Mfg mult-axis milling : Variable Contour Surface Area & grid errors

(OP)
Where I am: I have an inch assembly in a mm master model of a freeform, but primarily-continuous, design. I am doing multi-axis milling programming. I have to do various geometry additions to the component because of limitations in the physical production process. I am creating extra, also nominally-continuous surfaces on the edges of freeform design surfaces that I have divided with planes. This is a complicated explanation to tell you how I have arrived at my request, but my request is simple: which tolerances should I attempt to loosen to make my surface area grids work without error? Which ones should I avoid loosening or place limits on loosening?

What has not worked:
  1. Using Surface Area drive mode (inside a Contour operation) to simply focus on the (Divided) surface I want and then extend that surface by %'s (in the Drive dialog) or by diagonal points. The failure mode of this is that the extension of my surface area keeps wrapping around a continuous shape of the design instead of extending in a tangent direction to the edge of the selected Divide surface. It would be great if tangent extension was a selectable option
  2. Using Guiding Curves drive mode forces me to select more geometry like Part and Cut Area. When I go through that exercise and it violates the part, selecting Check surfaces is just too much for NX (on an HPZ420) to handle. It churns all night.
  3. Using linear Extrude on the edge of a freeform surface. It's tough or impossible to choose a vector for Extrude that will keep the joint between a freeform and a flat extension approximately continuous.
What has sometimes worked:
  1. divide my continuous design surface with a plane
  2. use the edge of this division as the seed curve for a sweep surface
  3. create guide curves off the design surface by A] Composite-duplicate my design curves B] Curve Length-extend them
  4. if an error reports that these guide curves are not tangent, loosen the Modeling Preferences / General / Distance Tolerance from 0.01 mm to 0.1 mm
  5. sweep my Divide edge off of the part with these guide curves
  6. Divide the Sweep into on-design-surface and off-design sections
  7. use the Sweep (off-design) surface and design surfaces as the Drive for a Variable Contour Surface Area
The failure mode of the last procedure, which works about half the time, is the age-old error like "Cannot build grid... Grid May Work if Selection / Chaining Tolerance is Changed..." I have never seen changing this particular tolerance help a situation like this. What other tolerances can I mess with to make this work? Is around 0.2 mm the absolute top end that I should consider tolerancing? My process can handle at least that much, but following general shape is still important, which I will not be able to explain here.

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