[Issue 2823] non-planar base for pocket

[flachyjoe]

Hi,
Part Design Next allow using face as base for pocket. It's not ok for non-planar faces.
When I select a inner cylindrical face it results in a shift of the hole (as seen in attachment). For a double-curved the pocket is transversal...
I think face must be validate as planar before doing the function.
cf : issue #2823



OS: Debian GNU/Linux 9.0 (stretch)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.17.9896 (Git)
Build type: Unknown
Branch: master
Hash: fc4a1c6081e6625840d891a52bebcd57bd9cc522
Python version: 2.7.13
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 6.8.0.oce-0.17-dev

[ickby]

This is correct behaviour. A Pad (and pocket in opposite direction) are extrusions in normal direction. For a curved shape of course there is no single normal, hence a "mean normal" is used, which most of the time gives expected results, as seen in your case with partial cylindric face. For some faces, as a full cylinder one, the Pad/Pocket result in invalid geometries, as the extrusion does lead to self intersections.

I think you confuse the pad/pocket functions with an offset function. For planar faces, extrusion and poffset are equal, but not at all for curved faces. Pad/pocket does not do offset, for this either a different tool would be needed or a special pad/pocket setting.

[flachyjoe]

Pad/pocket does not do offset, for this either a different tool would be needed or a special pad/pocket setting.

I'm agree.

Even if it's a correct behavior - mathematically defined - it's not an expected result.
As it's almost unusable, I think it could be remove not to confuse users. The non-planar faces can be refused as base for pocket and pad as they are refused for "Up to face" parameter.