Geometric Condition

[mill/cad]

Hello,

I'm trying to model some knurling on a plumb bob that we have machined as a school project. The plans we were given were...poor and I decided to draw some new ones. However I am stuck with this error message saying that the operation cannot be preformed due to geometric condition. Anyone know what it is or why it happens, I can get it to pop up during various stages of the knurling. There are 2 different sections of different diameters that have to be knurled.

 

[Jim232]

Use a cosmetic knurl

In the real world, those knurls would not even be modeled anyway. There's no need. Just model the plumb bob geometry and then on the detail sheet, select a good view of the part and draw a few reference lines to show the extents of the knurl. Then simply call-out the knurl spec with a leader note. That's it. If you get questioned about it, just say, that's how it done. It's similar with threads. Nobody draws threads unless they're and integral part of the design or modified in some special way. That's whay, CAD delevelopers came up with the term "cosmetic threads" and developed a special way of handling them.

Jim232

 

[mill/cad]

geometric condition pt. 2

Can anybody explain what exactly a geomteric condition is, and how they are created / resolved?

Does anybody know of a website or some reference material where someone could find out what all these errors mean and how to fix them, sketching, modeling etc?

Which is the best book for SW 2006, the Inside Soliworks series or some other book?

 

[support]

Resulting in an invalid solid.

Hello mill/cad

"Geometric Condition" in this sense refers to a condition in which an invalid solid would occur if the command executed as intended. The geometric condition can also occur after the fact, meaning that the command executed properly but the result is a geometric condition that left the geometry unstable.

To understand the fully, you need to unsetand the definition of a solid and how the topology of a solid is used to mathematically determine if the solid is in fact a solid and not "open" or invalid. An invalid solid could be one where one or more of the surfaces of the solid intersect one another or when there is a "sliver" surface whose angle is less than the geometry tolerance.

A B-Rep (Boundary Representation) solid (virtually all apps use B-Reps now), can be proven to be topologically correct if its elements are appropreately connected (e.g., all edges are connected to two vertices and bounded by two faces) and it adheres to an equation known as Euler's formula (derived by the 18th. century Swiss methematician Leonhard Euler).

Euler's formula:

V - E + F = 2

where

V = # of vertices (points)
E = # of edges
F = number of faces

For example, this formula can be easily verified with a simple solid cube.

V = 8
E = 12
S = 6

8 - 12 + 6 = 2

This simple formula must be true after every command is competed. If not, then a "geometric condition" has caused it to be not true. An example could be one vertice miss-matched over another (outside the geometry tolerance) where a corner now has two points instead of one. This is just one condition. There are many more.

Now, there can be a geometric condition even if the formula is true. For example if one face of the cube is stretched into the cude and it intersects the opposite face. All vertices, edges and faces are the correct # but an interferrance is calculated.

This topology relationship between vertices, edges and faces is the root cause of why solids require more CPU time than wireframe or surface modeling. Every time you intersect a solid with any other curve, face or solid, the CAD system must determine the resulting topology is correct and the the resulting solid is valid.

This is also why there are so many recommended best practices for working with solids, to minimize CPU time and more importantly to minimize the complexity of the topology of the solid so that error proned geometric condition do not occur.

Take a look at all of our "techBits" located in the following category:

TechBits > Solids (from the above menu tab)

I hope this helped. Let me know if you have any questions. Go to Google and search for Euler's Formula to find some examples.

3DCADTips Support Desk

 

[gupta_9665]

Knulrling

well y ui waste ur time in modelling the knurlling

thr is no need and it will also make ur part heavier

just use the texture to add the knurling look on the face u want 2 have knulring


wish it works for u

regards

Deepak Gupta