How to Flatten everything in Autocad

You probably have a large AutoCAD drawing with a lot of blocks and layers, and you want to use it for 3D modeling, and then you discover the Z axis surprise ! the drawing is not flat... 

The drawing from top looks OK, it can be printed fine.

 

Top view

But when you see from another view, it's a total mess and it's completely useless for 3D modeling

 

Isometric View

As a 3D designer most of the DWG drawings I receive esp mass plans have Z axis mixed up, and when searching online I see the very same question circulating in Autodesk forums, some people may use the move, flatten command or proprieties to reset the Z axis to zero, it may work for simple drawings, but sometimes there are some very complicated drawings that require exploding some parts and will cause crashes or hangs especially if don't have a powerful machine or if you are under OSX (AutoCAD for MAC sucks!)

If your flatten command in Autocad is  working, you are looking for an alternative or online way to fix the draw, the best and quickest way to fix this nightmare is to import your drawing into Sketchup and re-export it again as DWG.

First you need to import you drawing into Sketchup and chose in the options the appropriate units.

1- Import the drawing in Sketchup

Once in Sketchup you will need to change the camera view from Perspective to Parallel projection from the Camera tab > Parallel projection

2- Change camera to parallel projection

After that you can export your drawing as DWG and form the file menu File> Export > 2D Graphic , chose DWG on the format drop down list, and full scale in the Options

3- Export your drawing as DWG

Now you can re-import your drawing back to AutoCAD (to be done by layer as Sketchup doesn't support layered DWG export) or to any other software of your choice whether  Sketchup or 3DS Max etc... and start modeling in 3D !!

Original on the left - Flattened on the right

If you don't own a Sketchup pro license, no worries ! you can download a 30 days trial version from Sketchup.com and use it only for imports and exports, The trial counts time only when the software is running so it will last for an eternity ! Conserve your minutes ! 

It may also be very useful for other file formats conversions like SKP DWG DXF 3DS DEM DAE KMZ OBJ and FBX.