The purpose of the Instructable is to show the viewer how to design furniture to be cut using a Computer Numeric Control (CNC) machine. CNC furniture can be designed to use minimal supplies and no fasteners by using a series of components in tension and compression.
Materials and Tools:
Computer with Google "SketchUp".
Construction material of choice
Note: Experience with SketchUp and a CNC machine is HIGHLY recommended.
Step 1: Choose What to Build
Choosing what to build is a crucial first step to designing an object to be made using a CNC machine. Flat objects and patterns are much easier to design since the object only needs to be drawn in two dimensions. Puzzles, engraved maps, and game boards are great examples of easy two dimensional projects that can be made using this technique. Working in three dimensions adds a level of complexity to the project because material properties need to be considered much more thoroughly.
Consider the following when choosing an object:
- Limit number of pieces to under 10
- Object should consist of horizontal and vertical elements only
- All pieces should either be in tension or compression on object
Step 2: Make a Simple Sketch
- Simplify the chair into a stick diagram.
- Identify all individual components of the chair.
- Determine which elements are going to be in tension and which are going to be in compression.
Tip: It is helpful to draw colored arrows when determining component properties; blue arrows indicate components in compression and red arrows indicate ones in tension as shown.
4. Place components in tension near ones in compression.
Note: It is important to put components in tension near elements in compression because no fasteners should be used in the assembling process. The individual components of the chair, when assembled in the correct order, will hold each other in place.
Step 3: Draw Components Using Sketchup
- Determine maximum dimensions of project.
Note: The design shown has a maximum allowance of 2ft x 4ft to allow four individual chairs to be cut from one sheet of 3/4" Plywood that is the standard size of 4ft x 8 ft
2. Draw individual elements using SketchUp
Step 4: Dimensioning Connections
- Draw holes to be cut into the "h" portion of the chair
- Draw the ends of each component to match the dimensions of the corresponding holes
Note: Making the ends the exact same size ensures a tight fit between vertical and horizontal components.
Step 5: Dimensioning Connections 2
1. Dimension all horizontal components to have the same internal width.
Note: the internal dimension is the width of the chair seat and back rest; 1' 4 1/2" in the diagram above.
2. Dimension the ends of compression elements to penetrate at least the width of the material.
3. Tension elements slide into place over other components and as such should extend well past the thickness of the material.
Step 6: Dimensioning Connections 3
1. Draw a notch at the ends of tension elements
Note: the notch should be adjacent to the edge of the interior width and should be the width of the material: 3/4" in this case.
2. Determine how far individual tension elements will slide to lock the assembly.
Tip: tension elements slide into their final position: the seat of the chair slides backwards 1/2" to lock into place. Be sure to account for the loss of length to ensure a tight fit when other elements are in place as shown by the red and blue components above.
Step 7: Order of Assembly
1. Arrange all elements where they will be positioned.
2. Insert all components except the final piece into one side of the assembly.
Note: One final piece should lock everything into place, shown here in blue.
3. Insert components into the other half of the assembly.
4. Force sides tightly against the interior width cuts
5. Slide all tension components into their final position.
6. Slide final piece into position locking the other tension elements in place.
7. If elements do not fit into place make the necessary adjustments.
Step 8: Export the File
1. Delete all markings, measurements, guides etc from the drawing
2. Move elements to use material as efficiently as possible
3. Convert drawing to black and white using the available styles
4. Export image as a 2D image
5. Save file as file type .DWG
Step 9: Use the CNC Machine
1. Use CNC Machine system dialogue to set parameters for cutting (laser intensity, RPMs etc.)
2. Import .DWG file into system dialogue
3. Make necessary adjustments to drawing such as scaling, line color, line weight etc.
Note: CNC machines use different line colors and weights to make different types of cuts be sure to use the appropriate ones for the material you have chosen
Caution: CNC machines are extremely dangerous; use great caution when operating one and be sure to follow all safety instructions.
A scaled version of the assembly is being shown being cut with a laser cutter but the process is the same for most types of CNC machines. When scaling the model the material thickness will be the controlling measurement; in the model shown the original material thickness was 3/4" but was scaled down to 1/8". It is important to use the material thickness when scaling to insure that the notches still slide tightly over their adjacent components.
Step 10: Assemble
1. Remove components from scrap material.
2. Follow order of assembly determined in step 7
3. If all elements do not fit into place correctly, make the necessary adjustments starting from step 4.
Step 11: Final Product