Project: Design and Fabrication of a Bookshelf (Make Something Big)

Machine(s): ShopBot CNC Mill | Material(s): OSB

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Official Assignment Description: 'make something big'

The purpose of this week's project is to design and build something big using computer-cutting techniques. As the resulting object was likely to end up in my house, I thought I might as well make it useful. My girlfriend wanted a bookshelf / tv stand, and that seemed like a reasonable project. My design and process were guided by the following goals:

• Simplicity and functionality above all else
• Scalability in design (if the design works, I would like to be able to easily and parametrically modify the design for different sizes and materials)
• Use as much of the 8'x4' OSB as possible

Design and Fabrication

Step 1: Create dimensioned drawings in Solidworks. I intended to make the design a function of three global variables: width, depth, and material thickness. Starting values were: 38",12", and 0.41" (manufacture spec = 7/16"). It worked in general...but I made the mistake of cross-referencing dimensions. As a result, it is possible to parametrically update the sketch, but it might not work as expected...so use the file below with caution.
Parts.SLDPRT

Step 2: Export sketch as .dxf file.
Parts_dxf.DXF

Step 3: Open .dxf in PartWorks2D, set material thickness, uncheck 'use origin offset,' edit and join necessary vectors, and Tbone fillet all concave right angles to ensure joints fit together.
joepro.crv

Step 4: Create tool path file. Set start and cut depth, tool, offset, and mill type. I used 0", 0.55", 1/4" double-fluted end mill, 0.125", and conventional. Check tool path in visual display. I created two files: the first one cuts a single piece (just to make sure everything is going ok), the second one does the rest of my parts.
joepro1.sbp , joepro2.sbp

Step 5: Secure OSB to ShopBot bed with screws at each corner and side. Screws in the middle might be necessary if extra precision is desired.

Step 6: Open files in ShopBot3, turn on ShopBot, load and secure bit, zero X and Y, run Z-zero program at center of board, set spindle speed, start spindle, start dust collector, and run path file(s).

Step 7: Sand edges to remove sharp splinters and check press-fit joints. For some reason (I never tracked this problem down), four of the joints were slightly misaligned (all others were ok). I used a reciprocating saw to trim joint edges so they would fit together.

Step 8: Assemble, and decide it needs a finish.

Step 9: Prime and paint. I used 3 cans primer and 3 cans paint.

Tips and Lessons Learned

1. OSB can vary hundredths of an inch in thickness; this makes precise press-fit joints difficult to design. If tight joints are critical, I recommend using a smaller thickness (try 0.37) and then sanding each interface individually.
2. Parametric design is very cool! I highly recommend it, especially if you plan using the original design to produce variants etc.
3. When painting, note that one side of the OSB is more 'shiny' and will make a better finish (and use less paint). Plan ahead and make these faces visible. Also, note that paint adds hundredths of an inch...so be aware in the event of press-fitting.

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