Trim and Untrim Surfaces

[jcnewbie]

What is the purpose of untrimming a surface when a surface is already trimmed ?

[Matt Berube]

A trimmed surface does not allow edges to be extended.

Using untrim gets you to a basic surface which can now be extended and is easier to work with.

[jcnewbie]

Thanks for the response back.

What makes a surface trimmed or untrimmed. Every surface I create in Mastercam is trimmed.. Is there a possible way of creating a surface in Mastercam that is untrimmed ?

[JimPAC]

I used Mastercam for over 10 years until my competitors started kicking my @$$ with
GibbsCAM, know I use it for quotes as well!

Now I cant stand the laborious mastercam any more.

Good Luck muddling / modeling!

[Matt Berube]

@JimPAC,
Isn't there a Gibbs Fanboi forum somewhere on this website ?

@jcnewbie,

Trimmed/untrimmed has always been sort of a non-issue for me. Usually if you import a surface model there will be a mix of trimmed and untrimmed surfaces. I believe that when a surface is trimmed MC thinks of it as a larger basic surface which has been trimmed to some sort of boundary behind the scenes... When you untrim it MC shows you the original base surface.

Basically I pay no attention to trimmed or untrimmed unless I need to extend a face or something then I untrim as necessary.

I think if you created something simple like a ruled surface between 2 lines or a flat boundary surface from a rectangle you'd end up with an untrimmed surface although I am not sure about this and I am too busy (read > lazy) to try it now.

I recommend you not worry about it too much. There are far more important things to fill your mind with.

[thebowman]

Originally Posted by jcnewbie Thanks for the response back. What makes a surface trimmed or untrimmed. Every surface I create in Mastercam is trimmed.. Is there a possible way of creating a surface in Mastercam that is untrimmed ?

http://www.rhino3d.com/4/help/Commands/Trim.htm

"Trimmed Surfaces

A trimmed surface has two parts: a surface that underlies everything that defines the geometric shape, and trimming curves that either trim away the outside portion of the surface or cut holes in its interior.

Those trimming curves exist on the underlying surface. The underlying surface may be larger than the trim curves, but you won't see the underlying surface because Rhino doesn't draw anything for the part of the surface that is outside the trim curves.

Only the underlying surface defines the actual geometry of the shape. The trim curves do not define a surface -- they only mark which part of the surface is to be considered trimmed away.

If you have a trim curve that runs diagonally across a surface, the trim curve itself doesn't have any real relationship to the control point structure of the surface. You can see this if you select such a trimmed surface and turn its control points on. You'll see the control points for the whole underlying surface, which doesn't necessarily have any connection with the trim curves."

Did this help?

[ObrienDave]

Also, in V9, if you have your trimmed surfaces visible, go Screen-Blank-UnBlank, that will show you the underlying untrimmed surfaces.
Assuming they are in a visible layer.