Tutorial/Blender to CAD

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1. Open Blender

Blender Startup Screen

2.Use the scale manipulator to flatten and expand the cube so it looks like a tabletop.


3.Go to the Add menu or use the shortcut Shift+A. Add a cube.

Table Leg cube

4.Use the scale manipulator to expand and flatten this cube so it looks like a table leg. Then duplicate this table leg 3 times.

Table Legs

5.Move the legs of the table so it represents a table.

Position Table Legs

6.Select all the legs and the tabletop, and then click joins on the left side of the window under Object.

Join Legs To Tabletop

7.Go to File on the top left corner and select export. Under the export select obj.

Export Table

8.You will get an export window. Name your file test (optional).

9.Once you have named your file click on the Export OBJ button, which can be found in the top right corner, to export your blender file.

Export To OBJ

10.Go to the BRL-CAD bin directory and give the command to turn you obj file into a .g file. This command exports the obj-formatted file to a .g file. The syntax of the obj-g command is

>obj-g input.obj output.g  

Don’t forget to enter a path for your files. To see all the uses of the obj-g command just enter “obj-g.”

11.Open mged. You will see two windows, a command window that is white and a graphics window that is black.

Command Window
Graphics Window

12.Select File and click open. Open you .g file that you just made.

Open .g File

13.Then click on Tools. Open Geometry Browser under tools. Double click on the top object to display it.

Click on Tools

Geometry Browser

14.Click on View. Select “az35,el25”

Change view

15.Click on Tools once again. Select the Raytrace Control Panel. Hit the raytrace button.


Raytrace Control Panel

Command Window Raytrace Complete

Once you have Raytraced, you should have an image the looks like this:

Graphics Window Raytrace Complete

16.Do you remember what the table looked like when we were done with it in Blender? It was upside down and now it’s on its side. Rotating the table reorients it correct way. To reorient your table the right way, enter these commands in the command window:

 sed default.1.1.b.c.s 
Command Window First command
Graphics Window First command
 rot –90 0 0 
Commands Window Second Command
Graphics Window Seccond command
Commands Window Third Command
Graphics Window Third command

Then Raytrace the table once again by going to the Tools menu.

Raytrace Again

With that final rendering your import is complete!


BRL-CAD, like most of the CAD industry, uses +Z for up. Blender, like most of the film industry, uses +Y for up. Using +Y for up has origins in the film industry where the image screen is the center of attention, X and Y form a view plane and Z is the depth or distance from the camera. Using +Z for up has origins in manufacturing and architecture where the object and scene are the center of attention, X and Y form a horizontal ground plane, and thus Z becomes the elevation or height dimension.