Exposing the addednum and dedendum coefficients as properties allows to
change the tooth length above and below the pitch circle. This makes it
possible to use the profile beyond standard full-depth systems, e.g. for
stub tooths and most importantly: involute splined shafts and hubs.
Gear objets created with earlier versions automatically get the
additional properties on document restore. Its values match the hard-
coded values used in earlier versions.
There is a change when creating *new* internal gear profiles, though:
Previously, an addendum coefficient of 0.6 was used, presumably to reduce
the tip length beyond the base circle in order to avoid a non-involute
edge. This method is one proposal from the "Handbook of Gear Design" by
Gitin M. Maitra, as referenced in the original source code comments.
However, Maitra also states that this reduction of the anual gear's tip
in turn requires an enlagement of the mating gear of 1.25 instead of the
ordinary 1.0. And it is only required for a low numer of teeth and/or the
mating gear being quite large (less than 10 teeth in difference, to avoid
interferences).
Because those additional requirements and conditions have not been
implemented, the previously used values have been incomplete anyway. Thus
I decided to not implemented this special case and use the standard
values of 1.0/1.25 for newly created external and internal gears alike.
Internal gears need special care for other kind of interference anyway
and the newly exposed properties now allow to do so.
There is no entry in the task panel for those advanced properties yet.
This is a pure refactor, without any change in visibile functionality.
However, the new structure allows easy addition of new properties without
breaking existing documents.
The goal of this refactor is to get rid of gear-specific knowledge from
the implementation and argument list. This is to remove the duplicate
definition of addenddum and dedendum that was hidden there.
This is in preparation for new features, to ensure we don't break
existing documents created with FreeCAD-0.20.
The fixtures have been created with the official mac build of
FreeCAD-0.20.1 using mostly default parametrization -- only the number
of teeth has been reduced in order to keep the file size low.
Fixes#7770.
Until Point-on-B-spline is actually merged this will result in a malformed
constraint. It will however still allow a trim of the B-spline to result in a
coincident constraint.
