Wednesday, November 18, 2009

Predictability With Direct Editing - Part II

In my previous post titled Predictability with Direct Editing I showed a simple example of what it means to get expected and predictable results with “direct” or “explicit” editing. It was a simple example in that the geometry was mostly analytic – planes, cylinders and cones. With this example I am adding much more complexity in that most all surfaces being represented are complex b-spline surfaces. This example will greatly push the limits of direct editing.
As I have mentioned before when pulling on faces using direct editing, the system needs to extend or shrink the adjacent faces, but should also properly take into account rounds, fillets and chamfers. This gets much more complex if the adjacent faces happen to be complex freeform b-spline surfaces. How well will the system extend or trim the surfaces? Can you get predictable and consistent results?
For this article I also created a simple video to show the example. I start with a simple cube and then using direct editing capabilities to deform several of the planar faces. If you are trying this on other CAD systems you may have to use other methods to get the complex surfaces, however it shouldn’t matter how you create the surfaces. Once you have them just add the rounds and chamfers to get the basic shape.
Hopefully the topology of your part matches the one in the picture. Pay close attention to how your CAD system creates the chamfers. Are they accurate? It’s a bit surprising how some modern CAD tools treat chamfers.

Now let’s try some direct editing.

Try this example on your favorite CAD tool. Can you get expected and predictable results? How well do the surfaces extend? Is chamfer and blend sizes maintained? Are tangencies maintained and accurate? Are the surfaces extended in a logical and predictable way? Are the chamfers and blends order dependent? Live rules and parametrics can help control change, but if you can’t get through the basics of change they add no value.
Even though I considerably increased complexity with this second example, besides adding blends and chamfers I still did not change the topology of the model. So perhaps sometime in the near future I can bring it all together, including complex topology changes, with a realistic part.


bcourter said...

Hey Paul,

Could you please publish the part and document the edits so we can try them in SpaceClaim?


Paul Hamilton said...

Here are a few more details of the model creation:
• The Rectangle I used was about 65mm x 80mm
• The cube was about 40mm tall
• To deform the planar surface I pushed on a corner control point for about 10mm
• I deformed 3 side faces and the top face
• I tried a simple pull edit of about 20mm to the front face before adding rounds
• Add two rounds at about 16mm
• After adding the two rounds I pulled on the end face about 7mm
• Then added a 45x45x5mm chamfer

Here are the details of the edits:
• Pull right side face 10mm using bottom back edge for direction as it should still be a straight edge
• Pull front face 10mm using bottom left-side edge for direction as is should be a straight edge as well
• Add round to bottom edge of chamfer of 3mm
• Add round to top edge of chamfer of 5mm
• Pull the right side face to make the part 100mm wide
• Pull the top face up allowing the top face to float based on side faces
• Pull the top face locking the size and shape for the side faces to adjust (movinf control points)
• Modify chamfer to 5mm to 8mm
• Modify vertical blend to 30mm
• Modify top side blend to variable starting at 20 in front and 15 in back
• Change front of blend radius to 30mm

jamie said...

Hi Paul

Really good video, I tried to recreate it in spaceclaim and ran into a problem with the chamfer. If it is a round then all works as you show but with a chamfer no chance also difficult to chamfer at all. This seems to be a weakness in spaceclaim as i have run into chamfer issues before. Looking forward to the next video.