Simple Plywood Shop Stool

I needed a small stool for my shop, and I didn’t have a lot of scrap material that was suitable so I thought I would see what I could do with a small piece of precut plywood sheeting that I got from my local DIY store for $20 CDN. I wanted to document the process of design, ideation, as well as fabrication and practise how to combine digital and traditional methods to create a piece of flat pack furniture. In the end, the process taught me probably more about what not to do :¬D) but the result was pretty good and is in use constantly. Here's what I did, and what I learned.

Supplies

This project was created using basic tools and supplies I had laying around, the only purchase was the plywood.

• 1 pc 3/4 in (19mm) thick plywood - 24 in x 24 in (61 cm x 61 cm)
• Fusion 360 (TinkerCAD etc would work just as well)
• 3D Printer (Craftbot +)
• Cutting tools: jigsaw, bandsaw, drill bits (CNC Cutter would have been been ideal)
• Shaping tools: disc sander, belt sander, sandpaper
• Fasteners: 6x 2 1/2 in wood screws, wood glue
• Finishes: black paint, wipe on poly

Step 1: Design Ideation

The first step was to think about the overall parameters of the project. I wanted it to be as tall as possible (for the material) and compact in terms of the area it took up. It didn't take long to figure out that a three legged design was really all you need, and that the legs could be nested together on the material, so the seat would be the part that took up the bulk of the material. At this point, I decided that was enough of a direction to jump right into Fusion 360 and start designing some alternatives.

Step 2: Design and 3D Printing

Because this is a simple set of parts made from sheet material, it was the perfect project to use 3D printing to model the different design variations. There is a lot you can learn from looking at a design holding it in your hands vs looking at it on a screen, which is why these kinds of models or maquettes are so valuable. You can also easily create these models using a thin sheet of wood, cardboard or foamcore and some glue.

The variations for the leg design compared a straight leg design with one that had a slight angle. Initially I thought I'd prefer the more mid-century look of the slightly splayed legs, but after printing out and assembling the two models I felt that the angled legs made the stool look weaker somehow. It didn't look that way on the screen, so this was a great example how being able to evaluate the design in real life revealed more than was on the screen.

After printing out a few different seat designs, it dawned on me that if I could split the seat shape into three pieces then there'd be an opportunity to position each piece to use the plywood as efficiently as possible, so that was the final direction I took.

Step 3: Final Design

Once I had figured out that the stool would be composed of a single leg and a single seat part replicated three times, it was a fairly simple matter to create it in CAD. One of the advantages of this approach is that you only have to model one leg and one seat 'petal' and then duplicate them in a circular pattern around an axis to create the full stool. The great thing about this approach is you only have to make a change to the profile of the one part and you can instantly see how it affects the overall look as the other parts update automatically. I used this to try different variations of seat and leg widths and corners, until I found one that I thought looked good.

The final design was printed out and assembled to evaluate as a miniature, as well as using the parts to figure out the best way to arrange them on the sheet of plywood. One final addition was a piece was placed underneath the seats as a way to increase the thickness of the material where the seat petals would be attached.

Step 4: Cutting Out the Parts

First off, at this point this would be the ideal project to cut out using a CNC router, as in the CNC Wooden Car Toy from a few years ago. Unfortunately I didn't have access to that technology, so had to do it using more conventional tools, with all of the challenges discussed below :¬D) If you are lucky enough to be able to cut it out precisely, then skip to Step 7 below.

Because we need 3 sets of identical pieces I decided to create some templates to try and make them as similar as possible. So if the best way to get the parts cut out was via CNC, the second best way would be to cut a template out of thin MDF or hardboard and use a router with a template it to follow the template. I chose to go the third best way.

I created the templates using the thickest piece of cardboard I had, drawing out the shapes based on the CAD files generated by Fusion 360 (attached below). Once I had the cardboard templates they were marked out on the plywood. Using a jigsaw, I rough cut out the parts leaving room outside the lines to fine tune the cut later.

Step 5: Squaring Up the Parts

So the first problem I noticed was that the blade on the jigsaw didn't create a cut that was perfectly perpendicular to the top surface of the plywood. So the next step was to use the bandsaw and disc sander to cut up to the outline and make sure the cut was square.

Step 6: Fitting the Seat

The next problem was the fit of the seat petals. As much as I tried to make them identical, they weren't. And because each piece touches the other two pieces across 4 different faces the differences are obvious. So I put them together and labeled them to keep the order the same and then began a process of marking a line parallel to a face, cutting to the line with the bandsaw or sanding stick, checking the fit and moving on to another face. In the end, only 1 or 2 sections on each piece needed to be modified until the gaps looked even. Using some sandpaper, I then put a small chamfer on all the top edges which help to give it the appearance of being nice and even.

Step 7: Dry Fitting and Tweaking

Once the seat pieces were fitted, I turned my attention to the legs and dry fit all the pieces together to check the fit. The cutouts in the leg need to be adjusted slightly so that the circular piece below the seat fit snugly. Additionally the tabs in seat needed to be adjusted once that had been done and it was ready for sanding and assembly.

Step 8: Sanding and Assembly

Just like any other woodworking project, there's some sanding in your future :¬D) Nothing special to note, I worked my way through 120 grit to 220 grit, paying attention to the edges as I like the look of the exposed plywood layers. I also sanded a slight chamfer on all of the edges to soften them a little bit and to disguise some of the imperfections.

To assemble the seat, the seat petals were placed upside down on the table and wood glue was added to the edges that will be touching. More glue was used on the underside of the disc which was also secured with some brads and the whole thing clamped together to dry.

The legs were pre-drilled in the location where the wood screws would be used in order to minimize the splitting by drilling through the laminations. There are probably better ways to join the legs to the seats, but this worked for me.

Once everything had been put together one last overall sanding was done and it was time for finishing.

Step 9: Finishing

I wanted to use a simple wipe-on poly for the finish, but my earlier enthusiastic sanding went right through the top veneer in a couple of spots so I decided to paint the top of the seat black. After a few coats of finish with some light sanding in between it was ready for use.

Step 10: Final Thoughts

I'm super happy with the way this stool turned out, and I use it all the time. It's much lighter than I expected and surprisingly sturdy. You do notice a bit of flex if you rotate around when sitting on it, but overall it is super comfortable to use. One of the reasons is that you can either sit by straddling a single leg or sitting on two of the petals at once - depends how much support you want, and where you want to put your feet.

Designing the piece in 3D and printing out the maquettes was very revealing, and extending that workflow to cut out the parts with the precision of a CNC cutter would absolutely make the whole thing even more precise and satisfying.