I recently had a need to place an aluminum panel in a trapezoid for a mantelpiece.  I decided to use the Shopbot so I could ensure a consistent depth for the recess.  

The attached video shows the recess being cut.

I do my work over at the Techshop in San Jose...

Step 1: Start With a Trapezoid Image Which Has the Same Dimensions As the Piece of Wood

For preparing drawings for the Shopbot, I generally start with CorelDraw.  Mainly because I'm most familiar with it.

The tool I used is called the Contour tool.   I made a 1-step internal Contour, about 1/4" from the original.

Select the Object (trapezoid)  --> Effects --> Contour.   Alternatively, you can select CTRL + F9 to get the Contour tool.

Step 2: Apply the Appropriate Contour

This process is pretty straightforward, especially since I wasn't worried about the colors or gradients or anything along those lines.

With the object (trapezoid) selected, I chose the following:

Offset - .25"
Steps - 1

Then I selected Apply.

Step 3: And We Have Our New Trapezoid, a Quarter-inch to the Inside of the Original

This is the new trapezoid I was looking for.

Now, CorelDraw allows you to separate the two trapezoids, but I did not want to do it.   So, I went ahead and added a curve (set of lines) that matched the internal trapezoid to use for my eventual export.  The next step shows this new curve.

Step 4: Use the 2-point Line Tool to Make a Copy of the Internal Trapezoid

I drew lines from node-to-node on the internal trapezoid.  I changed the color to red to make it easier to see.

This curve is the shape I needed to export to VCarve to prepare a file for the Shopbot.

I could have simply ungrouped the Contour pair (probably saving some time), but chose not to do so.

Step 5: Move the Red Trapezoid to a New File, and Export for Vcarve

I opened a new file and added this new trapezoid.

I then went to File --> Export --> Save as Type --> DXF (using the AutoCad R10 option)

Step 6: I Opened VCarve Pro to Get Ready for My Drawing.

I set the following in VCarve Pro for my piece to be cut.

Job Size
Material Thickness
XY Datum Position

This data matched the piece I was using - your needs may be different.

Step 7: I Imported My Trapezoid

File --> Import --> Import Vectors

I selected the dxf I created in previous steps.

Step 8: And I Prepared a Toolpath

Once I'd imported and moved the trapezoid onto the VCarve canvas, I created a toolpath.

Since I was using a 1/8" router bit, I used this info to set up the Pocket Toolpath, and carved down to 1/8".

The output file was a Shopbot Arc (inch)/with speed .sbp file.

Step 9: And I Cut My Recess.

After aligning my piece and testing the alignment with some sacrificial pieces, I was able to cut a very nice recess.

I had to use a knife and chisel to complete the corners which had a 1/8" radius, since I wanted sharp corners.  

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