Thursday, 30 January 2014

The Ten Commandments of Solid Modeling Part2

This is part 2 of the list of rules that help novice users and 3D experts alike, generate robust and solid models.
These 10 rules can save hours of work each day by saving drafting (layout) time, ensuring adherence to company standards, and allowing changes to be easily absorbed, with little effort on the your part.

Index of all Solid Edge tutorials and tips is here.
...continued from Part 1

Chronology of Fillets

Create Fillets as late as possible.
Just as drafts should be created as early in the model, fillets should be created later.
Filleting the edge of a face prevents that face from being drafted later. The extra edges created by fillets becomes selectable as reference for later features, and can therefore cause parent-child relationships that are undesirable.
Few models will have all the fillets as the last features, but creating them as late as feasible in your design allows more design freedom.


Chronology of Shells

One caveat to the rule about creating fillets late is that shell features should be created after fillets that can affect the shell.
In order to create a shell object with constant wall thickness, it is a good idea to have the outside fillets created before the shell is created.
By doing this, inside filleted edges are created that are smaller or bigger than the outside fillets by the wall thickness, resulting in a constant wall thickness everywhere.


If the fillets are created after the shell feature, the radius of the fillet has to be approximately equal to, or less than the wall thickness.

If an outside fillet becomes larger than the wall thickness, the feature can fail.
This can be prevented, by using the Variable Table functionality to limit the radius size, but in most cases it is simpler and more advantageous to avoid this completely by creating the outside fillet before the shell.



Chronology of Fillet Radius

Apply larger rounds first.
Suppose you apply the small round first. And then the larger round.
Not only, Solid Edge senses it as a feature with problems, but the result is also not the desired one.



You can rectify this problem by dragging and dropping the last round feature before the previous one in the feature pathfinder.
This is also called feature re-ordering.
And even though, feature reordering is a handy tool, apply larger rounds first.


Parent-Child Relationships

Be aware ( not beware! ) of parent child relationships.
Parent-child relationships help capture design intent, but can also be a source of frustration if used haphazardly.
Dimensioning a hole to the edge of a protrusion, makes the hole a child of that referenced feature. In this case, if the protrusion is deleted, then the hole no longer has it's parent, and the child becomes a failed feature.
In this case, it is recommended to dimension the hole to the edges of the face on which it is created.


Here is a list of some methods that create parent-child relationships :

  • Dimensioning to existing geometry.
  • Coincident, collinear, tangent, parallel and perpendicular constraints between profile geometry you are creating and existing model geometry.
  • Workplane location reference. Any surface used to locate a new reference plane and then features created on the new reference plane.
  • Mirroring a feature.
  • Grand Children A child of a feature that is itself a child of another feature.

  • t3414[4]


    Prefer cutouts to holes

    Whenever possible and if the design allows, use a cutout instead of the hole feature.
    Using cutouts instead of holes reduces the file size.
    Especially when you have large number of holes (for e.g. 12 flange couplings with 12 holes on each flange - total 288 holes/cutouts).


    Creating your own, brand new, fully functional CAD system with 3D sketching and surfacing capabilities using a geometric modeling kernel is equally simple and interesting

    cMayoCAD from CADVertex is one such program.

    Download the detailed course contents for cMayoCAD here.