Combine multiple surfaces from former STL File

[Anonymous]

I have the STL file of a snowflake that I converted to a .dxf using the helpful STL2DWG converter. When I load this file into AutoCAD, it looks great. 

GOAL

What I am trying to do is determine the total volume enclosed by this shape. I also want to calculate the moments of inertia. Naturally, I thought I would try to create a 2d projection of just the outline, then extrude this to the proper height. Or perhaps merge all the objects into one.

PROBLEM

I cannot seem to manipulate this collection of objects. Flatshot reported that there are no surfaces to be projected. MERGE/UNION don't work. Converting to a surface did not work. I tried messing with layers but no luck. I could not figure out how to create a 2d projection. I feel like I have exhausted my options, though I am sure there is a way to accomplish my goal.

I would greatly appreciate any help someone might be able to offer. 

[leeminardi · Accepted solution]

First, make sure your active layer is ON!  In your drawing it is off.  Also, in general do not use layer On/Off.  Use Freeze or Thaw instead.

Try the following.

1. Create a new layer (I named it solid) and make it active.

2. Get a front view and delete all the geometry that is not on the XY plane.  This is easy to do with a select window from right to left.

3. Go back to the Top view and give the Region command and select all the faces of the snowflake.

4. Give the Union command and select all the faces.  This will yield a single region the shape of the snowflake.

5.  Use Extrude to make it a solid 1.5 units thick.

You can now use massprop to get the mass properties.

~Lee