About the Design

With a substantial amount of joinery packed into a few small, simple parts, the Rotational Stools are an ideal first project. Both stools share the same overall outer dimensions, and both are comprised of five pieces, with two part types. Each stool has four identical leg parts, which are organized into a rotational structure that interlocks into the seat (see “Structures”). What differentiates the stools is how each utilizes different types of joinery. Lazy fingers are used to join the “Lazy” stool (left), while the “Lively” (right) has tight, through connections. While originally designed as small stools, many find that the pair work equally well as mini side tables.

Before You Begin

To cut a pair of Rotational Stools, you only need a partial sheet of 4’ × 8’ × ¾″ material. However, you may prefer to purchase an entire sheet, so you can use the surplus to prototype, troubleshoot, or experiment by cutting the project several times.

Since they are already quite small, the Rotational Stool file isn’t accompanied by a test piece (explained in “Test Pieces”), but we will employ that technique in other projects in this book. For this project, it’s possible to cut several versions from a single sheet of plywood, so you can test various CAD scaling and CAM setting combinations, and learn the variables that factor into achieving a perfect joinery fit.

Measure and Scale

If you went through “Job Setup” without measuring your material and scaling your cut file, proceed with these steps to prepare a CAD file and CAM settings.

Figure 8-1. How to measure and scale the Rotational Stools

Refer to “Selecting Materials” for guidelines on plywoods and follow the instructions in “Measure Your Materials” to measure your sheet material and identify its actual thickness, T^MAX. Divide T^MAX by T^NOM to find your scaling percentage (S).

Download and open ATFAB_STL.skp. Refer to “Scale Your CAD File” and scale all Rotational Stool part toolpaths by S so that they match T^MAX. Import this scaled CAD file into VCarve and follow “Job Setup” to define toolpaths for your scaled file. Once you have saved your scaled toolpath operations for output, you are ready to fabricate.

Cut and Evaluate Fit

Proceed with cutting your first set of parts on the CNC. After cutting is complete, gather all cut parts from the sheet, dust each part off, and stack similar parts together on a work surface.

Evaluate the Lazy Stool

Piece together several parts of the Lazy Stool, handling each part carefully. Hold parts so that they are squarely aligned and feel the face of a tab relative to the face of the adjacent part. Is the tab flushly aligned with the face? Or does the tab extend beyond the face (or vice versa)?

While perfect flushness between these two surfaces is your objective, the Lazy Stool will still be functional even with parts that are less than flush. The Lazy Stool has edge-to-edge and edge-to-edge-to-edge joints, which are more forgiving than the interlocking through and end-to-face connections of the Lively Stool. You won’t really know how well your parts fit until you test complex, multi-sided joinery, like the connections found in the Lively Stool.

Figure 8-2. Cut parts for the Lazy (left) and Lively (right) Rotational Stools

Troubleshooting

Don’t get discouraged when your first round of Rotational Stool or test piece parts don’t fit. When starting out, easily assembled, perfectly aligned joinery doesn’t always happen after the first or second attempt. Getting to the perfect fit simply requires additional scaling, or minor adjustments to machine settings, and re-cutting of your adjusted test pieces. This process may feel quite tedious at first. However, taking these extra steps at this stage will ultimately give your furniture square joinery, solidity, refinement, and a long, useful life. And, the more you go through the process of troubleshooting, the more knowledge you’ll gain about digital craft, and the better you will be able to anticipate. When troubleshooting, start by identifying the problem and then planning a course correction.

Assemble

After you have successfully cut a pair of Rotational Stools with parts that fit perfectly, you are ready to assemble them. Collect your parts, and very lightly file or sand any rough edges. Keep the sanding block and file parallel to the edge and don’t oversand or round the edges. Carefully dust off each part and stack similar parts together on a protected work surface. It helps to use a cloth or moving blanket, so as not to scratch the parts or damage the worktop.

Figure 8-3. Assembly diagram of the Rotational Stools

Prior to assembly, gather your hardware and matching drill bit, drill, and blue tape, as well as an Allen wrench or screwdriver that matches your fasteners. Place everything within easy reach. Lay your recently cut stool parts out in the order of assembly, with the right sides facing upward.

The Lively Stool is best assembled upside down. First, place the seat with the top facedown on your work surface. Interlock the four legs and snap the four leg tabs into the center hole of the seat. You might find blue tape and an extra set of hands especially helpful in keeping the Lazy Stool parts together during assembly. Start by placing the seat with its top facedown on the work surface. Piece all four legs together and secure them firmly with blue tape.

Figure 8-4. Lazy and Lively Rotational Stools

Fasteners

Since the furniture joinery does most of the structural work, the lighter load on your fasteners means you have some flexibility in your choice of hardware. Fasteners ranging from wooden pegs to heavy-duty industrial fasteners to the lightest of screws will do the job and can be as minimal or as expressed as you want.

Wooden pegs, either prefabricated or cut to size from dowels, create a subtle inlay detail against plywood parts. Since pegs are glued into place, they are best used for furniture that won’t be dismantled. Peg and hole diameters should match so that the peg fits through the hole, requiring a bit of pressure. Length should be about twice your material thickness (2 * T^MAX). Dowels are best inserted with a very small amount of adhesive in order to fix the furniture parts and the dowels themselves in place.

Figure 8-5. Length (2 * T^MAX) and diameter (1/3 < T^MAX) fasteners pass through pilot hole and into opposing part

If you intend to dismantle a piece of furniture, or you just like the ease and appearance of hardware, it’s best to use screws that are easily removed and reused. Polished finishes are often better at reflecting the furniture material, so they end up blending in to the surrounding material. Like dowels, fasteners should be about twice your material thickness (2 * T^MAX). Any less and the fasteners aren’t bearing deeply enough into the material, and any longer demands more drilling and screwing than is really necessary.

Fasteners should match the hole made by your CNC router so that the shank passes through the hole with threads just grazing the interior. The screw head diameter should always be greater than the hole diameter. Select a thread diameter no greater than one-third of your overall material thickness (1/3 < T^MAX), which should ideally match the hole made by your CNC router. We often work with Stafast decorative screws, particularly the small, flush-mounted SCS0540HD. With a length of about 1 ½″ and shank diameter that fits within the 1⁄8″ fastener hole, the screw is perfectly sized for ¾″ plywood parts.

How to Drill

While the CNC router predrills holes into the face material, you’ll still need to manually drill holes into the edge of the opposing part for pegs and hardware. Predrilling holes for pegs is a necessity. Though predrilling prior to screwing in fasteners may seem optional, it’s actually a good practice for many reasons. It prevents splitting of the plywood plies, and also allows a clean contact between the fastener threads and the hole. Also, you’ll have a greater choice of fasteners, if you’re not relying on self-tapping screws.

Use the hole cut by the CNC as a pilot hole, helping you perfectly locate the fastener and align your drill.

1. Piece furniture parts together and secure with blue painter’s tape (Figure 8-6).

Figure 8-6. Drill through pilot hole

1. Predrill all holes for fasteners (Figure 8-7). Start by working around the sides, before drilling seats and tops. For furniture pieces with feet, save the feet for last. Drill directly through the pilot hole cut by the CNC machine, keeping your bit perpendicular to the face. Drill into the edge of the opposing part, matching the drilling depth to the length of your fastener.

Figure 8-7. Insert fastener

1. Screw in fasteners, matching the drilling sequence. Start by securing the sides to each other first, then attach seats (or tops), and then feet (Figure 8-8).

Figure 8-8. Tighten fastener by hand

Consider the starting point and sequence of drilling and fastening. It helps keep joinery aligned when you drill and fasten from the center of the furniture and work outward to the edges, corners, and feet. Working methodically will also help prevent missing a hole!

Be careful not to over-rotate when screwing fasteners into the material. Heads should be flush, and not pressed into the face veneer.