CAD a Baffle Box for Noise Reduction in Inventor

Here at TechShop  we built a vacuum table for our CNC router (ShopBot).  It uses 6 separate impellers that are very very loud.  This Instructable is how to build a file ready for CNC routing using Autodesk Inventor.

To begin, lets talk a little about what a baffle box is.  It's a box that contains baffles.  To quote wikipedia: "A sound baffle is a construction or device which reduces the strength (level) of airborne sound. Sound baffles are a fundamental tool of noise mitigation, the practice of minimizing noise pollution or reverberation. An important type of sound baffle is the noise barrier constructed along highways to reduce sound levels at properties in the vicinity. Sound baffles are also applied to walls and ceilings in building interiors to absorb sound energy and thus lessen reverberation."  For this to work in a box or along a highway the sound would need to make at least two 180 degree turns.  Why not just box it off completely?  Then we wouldn't get airflow.  Why not use a dampening device?  It's my instructable and I will do it as I want...also maybe a fire hazard.  And when you have a CNC router...well you start seeing everything as a CNC rout-able.

For this we are using A/D Inventor 2012, and 3/4" MDF.  Our motors and mounts are 11"x11" squares that extend 7.5" underneath the table.  Units are in inches.

1) Draw a rectangle that is 13.5 x 13.5. (Fig. 1).
2)  Extrude to 15.75 (Fig. 2).
3) Use the "shell" tool and remove the faces on either of the long end.  Se the thickness to .75 and shell inwards (Fig. 3).
4) Chose an inside face and create a sketch.  Select "project cut edges" from under the "project geometry tool."  Press F7 to "slice graphics" so that you can see the sketch.  Draw three .75 thick rectangles with the dimensions as shown.  The should leave a passage for two inches of airflow from the inside rectangle (Fig. 4).
5) Extrude the rectangles "to next face/body" (Fig. 5).
6) Select an adjacent inside face and create a new sketch.  Again project cut edges and slice graphics.  It should look like Fig. 6.  Finish the sketch without any extrusions.
7) Repeat step 6 with the opposite inside face (Fig. 7).  Note Figures 6 and 7 will be reversed depending on which face you have selected first and second.  It does not matter.
8) Repeat step 6 with the two remaining inside faces. One is seen in Figure 8. IMPORTANT-- Make sure to project cut edges and then draw a rectangle over the inside rectangle in order to make .75 on each side (left and right).  This will allow a place for the MDF sheets to lie against the face you are looking at now.  In the end, you should have two rectangles that are 13.5 wide and two that are 12 wide. 
9) Export each face as a unique .dxf (AutoCAD file).  To do this, right click on the sketch in the browser to the right as show in Figure 9.  To illustrate what each face looks like in 2D you can see Figure 9 which are imported .dxf files into my CAM software.

Attached are the .dxf files for each side and the baffle (of which we need three).