Extrude vs. Offset Question

[neljoshua]

I imported an .stp model of a TI chip from Digikey and am going to use it in my design.  This is a combination electrical/mechanical design, so I need the size of the chip as well as its connections.  The model came in with some unnecessary geometry, so I wanted to clean it up.  Take, for example, the line on the top face (which is planar but is split in two).

As it is already a solid body, I was not able to use the stitch tool.  Nor was I able to simply delete the line.  I thought that maybe the push/pull tool would be useful, so I selected one of the top faces.  When I use this tool, not only does it repair the top face, but any adjacent faces as well.  This is curious to me.  The extrude tool produces completely different results, extruding only the selected area and not affecting adjacent faces.

This could well be another thing that I do not understand, but can anyone tell me:

a) why if the top surface is made out of two faces the offset and extrude tools produce different results, and

b) why adjacent faces are modified during the offset command?

Design is here and a screencast is below.

[JDMather · Accepted solution]

Watch this video for tip on deleting and healing those faces.

http://au.autodesk.com/au-online/classes-on-demand/class-catalog/2016/fusion-360/pd16277#chapter=0

[TrippyLighting]

The extrude tool has one purpose, it makes a linear extrusion perhaps with a taper isa defined.

The Push/pull tool is a meta command that does things depending on what is selected. If you select an edge it'll fillet it. if you select a face it will move the surface along it's surface normal(s).

I guess that it attempts to do that too with the top surface of the chip and heal it in the process.

[Oceanconcepts]

You have triangular faces (not lines) everywhere, from what I see. The triangular faces may indicate the file was once a .stl (?), not sure why but I see this often.

A surprising number of times just selecting the extra face and hitting delete will heal the surface. This may work better if you are in Direct Modeling. Quick and dirty would be to split the body with a plane, then extend the resulting surface to the original position.  Not so easy if you want to simplify all the faces, though. I have sometimes found it easier to just section models like this with a mid plane, project the relevant points to a sketch, and extrude, or extrude and pattern if you have lots of pins, then delete the original reference. 

The video JD linked to is a great illustration of why I like working in direct modeling for developing concepts and simple parts that won't change. 

Digi-Key doesn’t always have the best CAD resources- or for many parts, any resources at all. One place I go for electronics, particularly for standard packages, is 3D Content Central: 

http://www.3dcontentcentral.com 

An increasing number of manufacturers are providing 3D CAD models for electronic parts, those don’t always make it to Digi-Key, so it's often worthwhile to check their sites.

[neljoshua]

@JDMather, @TrippyLighting, & @Oceanconcepts,

Thanks for the tips.  I am going to take a look at the video later (after work).

Deleting the extra face does indeed seem to work.  Surprisingly, it also deletes the extra faces on other surfaces as well.  It just seems weird to me.