Update 2010-08-24: There is a new extension which does a better job of exporting to DXF from Inkscape: Big Blue Saw's DXF Export for Inkscape.
I often recommend Inkscape to people who are new to Big Blue Saw and CAD design. Inkscape is a a zero-cost, open source drawing tool that's simple to use, but also quite powerful. If you need very precise lines and curves in a design, you need to use software like Inkscape, which can create and manipulate vector graphics.
Our own Big Blue Saw Designer is useful for creating many kinds of parts, but it doesn't have the file import/export capabilities or sophisticated curve and shape tools that Inkscape has.
The example below created using Inkscape version 0.47. Follow along with it to see how you can design a simple part using Inkscape.
Here is the part we will be making. Two of these parts can be slotted together to form a small square stand, perfect for elevating your rubber duck to protect it from passing predators, among other things.
Here is what Inkscape looks like when it first starts up. What a wonderful selection of buttons and controls! The main area depicts a piece of letter-sized paper to help you have some idea of the scale of the drawing.
We will start by drawing a square for the outline of our part. Click on the rectangle drawing button, then drag in the document area.
Next, you want to resize the rectangle so that it is a precise 2 inch square. On the toolbar, there is a drop down list which shows the measurement units for your new rectangle. By default, this is set to "px" (pixels). Change the units to "in" (inches). Then enter "2" for both the width ("W") and height ("H") and press the Enter key on your keyboard.
Now you are ready to create the slot in the edge of the square. Using the rectangle tool as before, draw a thin rectangle near the right size and location.
This creates a another black shape, which is hard to see against our existing black outline. Change its color to white by clicking on the palette just underneath the drawing area.
Now switch to selection mode by clicking on the selection tool on the tool palette on the left-hand side of the window.
We want the slot to extend halfway down the square and be just wide enough to accommodate a 0.236 inch thick piece of acrylic. So on the geometry toolbar, after making sure that the units are set to "in", enter "0.236" for the rectangle's width and "1" for its height. Then press Enter.
The slot needs to extend from the top-center of the outer square to the middle of the square. We can get the slot in the exact position by using Inkscape's alignment tools. Click on the slot rectangle, hold down the Shift key, and click on the square. This will cause both objects to be selected. Open the Alignment panel by choosing Object | Align and Distribute from the menu or by or using the keyboard shortcut Ctrl-Shift-A.
Click the "Center objects horizontally" button to place the slot in the middle of the square.
Then click the "Align top edges" button to move the slot to the top edge of the square.
To get a better idea of how Inkscape will export the file when you are ready to send it to Big Blue Saw, switch to outline mode by choosing View | Display Mode | Outline from the menu. This will hide the fill colors of the shapes and show all lines with the same width.
If you take a look at Big Blue Saw's FAQ on vector file formatting, you'll notice that we need to make sure that the lines in our file trace the outline of the part and do not cross. The drawing is not quite right at this point; the top of the slot is still closed off. At this point, we can make the smaller rectangle a cut out from the larger square.
You will need to make sure that the slot crosses over the outline of the square. This will ensure that the square's edge follows the contour of the slot. Make the slot slightly taller by clicking on it and dragging the center resize handle at the top.
Now add the square to the selection by holding down the Shift key and clicking on it. Choose Path | Difference from the menu cut the slot from the square.
The new object is a square with a slot cut in it. It's a little hard to see because Inkscape displays a dotted line around the currently selected objects. Click on the background to remove that outline and see the just the outline of your part.
At this point, the file is ready to be exported for use with Big Blue Saw. Choose File | Save from the menu and pick "AutoCAD DXF R12 (*.dxf)" for the file format.
After you click the "Save" button, you will be prompted for several "PostScript". Just leave these at the default.
At this point, you have a DXF file suitable for use with Big Blue Saw. You can upload the file to our online quotation system. From the online quotation system, you can choose your material, and order your part online.