Three dimensional (3D) design is fantastic. I have been using three dimensional design CAD tools for over 25 years. (Even if I have a two dimensional project, I generally model it in a high-end three dimensional CAD tool.) You can probably tell from my instructables member name that I am a big fan!
Three dimensional fabrication methods, such as multi-access mills have been around for a long time, but it is the recent explosion in three dimensional printing methods, such as the Dremel 3D Idea Builder, that has enabled many designers and inventors to realize their dreams.
However, there still exists the need for high-end, high-resolution, two dimensional fabrication methods. These include CNC (computational numerical control) routers, laser cutters, plasma cutters and water jet cutters. These machines allow you to quickly and accurately cut parts from flat stock, such as wood, sheet metal, plastic, fabric, and even stone.
This tutorial will illustrate the steps necessary to transfer three dimensional designs, to two dimensional data for fabrication.
Step 1: Create your 3D design
Let's take a look at the three dimensional design for our playing card holder. Three dimensional design allows us to make sure our parts will fit together, as intended. With three dimensional models, you can quickly and easily create cross sections to verify your part's fit, function and form.
One of the most important things to remember at this stage, is that you ALWAYS want to design your three dimensional parts and assemblies at their full size.
Step 2: Create 2D Drawing
Create a two dimensional drawing of your three dimensional part(s) in your CAD program. Most CAD programs will prompt you for a sheet size (A, B, C, D, etc.) Completely ignore those prompts, and select 'Variable' or 'User Defined' (or whatever your CAD program calls it), to allow you to enter your sheet dimensions manually.
Standard A size drawing sheet is 8-1/2" x 11". (This is a typical printer and copier sheet size in the US). B size is 11" x 17" (the same as two A size sheets next to each other.) C size is the same as two B sheets (17" x 22"), and D is the same as two C sheets (22" x 34"). So if you were to fold a D size sheet three times, changing the direction of the fold each time, you would end up with an A size.
So what size sheet should you create? Make sure your drawing units are the same as your part units (mm or inches) and create a sheet with the same dimensions as your work piece (the piece of material you are going to be cutting from). In this case, the work piece measure 19-7/8" x 6-3/16". We went ahead and rounded our page size to 19.9 x 6.19, definitely not a standard size.
Add a general view of your part(s), in whatever orientation needed for cutting your shape(s). Since your sheet is the same size as your work piece, position the view(s) where you would like the part(s) to be cut. In the case of our card holder, we needed to avoid a few knots in the wood. By creating the sheet the same size as the work piece, we could easily arrange the views to create the cuts where we wanted them on the material.
The key here again is to be sure that both your drawing sheet scale and your view(s) are at 1:1 (100%).
Step 3: Export .DXF
From your two dimensional CAD drawing, export/create a .dxf file.
Drawing eXchange Format (DXF) was created by Autodesk (creators of AutoCAD) to transfer (typically two dimensional) data between software programs.
The DXF format is ever changing, and not all manufacturing programs will accept the latest versions of DXF, so it is best to 'dummy it down' a bit. When creating/exporting your file, select AutoCAD 2000 or earlier version as your output type.
Each CAD system will have slightly different ways of exporting the .dxf file:
Because your drawing and views are sized at 100% scale, the resulting .dxf file will be the exact size for cutting your part(s). If the border of your drawing sheet was visible at the time of its creation, the .dxf file will also contain the boundary of the work piece. This is very useful, because the corner of the .dxf will be located at corner of your work piece, and will correlate with the 0,0 (origin, usually bottom left corner) of your CNC cutting software.
Also, the .dxf file will be in vector format, meaning it will contain line data without thickness.
Step 4: Import .DXF
Open or import the .dxf file into the software you will be using to control your fabrication/cutting tool.
In the case of a laser cutter, you can typically use CorelDraw or Adobe Illustrator, and set all of the lines, circles and arcs to 'hairline' or 'zero' thickness. When cutting with a plasma or water jet, programs like Flowpath will also read the .dxf as a zero line thickness vector file.
When driving a tool such as a ShopBot (CNC router), programs like VCarve Pro can be referred to as '2-1/2D', by using the imported vectors to define X and Y (two dimensional) boundaries, and adding a Z value (third dimension) with user input.
This is how the cutter paths for our card holder were created. After reading in all the 2D data, we assigned cut depths to the various lines and boundaries. Because the .dxf file did not contain any of the depth information, we simply used our original 3D CAD model as reference when entering the values into the VCarve software.
Step 5: Cut your 3D parts!
You may notice a slight difference between the graphics on the previous steps and the photos and video shown here. That is because use created several of these card holders, with each one needing a unique layout to avoid defects in the wood. This was easily accomplished by making the drawing, .dxf, and VCarve files the exact dimensions of our work pieces.
Note the progression of the design:
3D virtual CAD model > 2D drawing > 2D .dxf > 2-1/2D cutter path > Real 3D solid object.
Sometimes you need to take a step back, to move forward!
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