Live Edge Dining Room Chair From One Slab

One Slab Wood Antelope Valley Dining Chair and All Wood Joinery [yup, no metal].

This was a 2-week college design project for a team of two.

Goal: Design a dining room chair using CNC shopbot Alpha, with at least one part 3D CNC'd. The theme was Nature. Since it was Nature, we designed to have have zero waste and no metal parts. All parts of the wood was going to be used.

We chose the contours from the Antelope Valley after considering several natural ideas ranging from leaves, branches, organic patterns, and freeform shapes. The contour lines lent itself to the grains of the wood we chose - a slab of elm. The slab was just over 2" thick and over 50" long x 15" at the widest part. We bandsawed the thickness in half - a rather miserable job as the blade was relatively dull. Still, we didn't burn the wood! BUT, it was rather uneven and somewhat 1" or so thick in most places in the two slabs.

The slabs were too wide to run through the planer, and we didn't know about surfacing with the CNC, so I learned about zero-ing the Z-values along the way. Because I did not want to leave holes from the mounting of the stock, I got creative in bracing the slab while selectively running tool paths. I will not be going into detail about the CNC part as that can be different for each type of CNC. This whole project can also be done without a CNC, using routers, table saws and hand tools.

Here is a set of mock ups we made out of black foam core.

Originally, our lofty plan was to have blue epoxy resin between the live edges, but we ran out of time, and money. We were students after all! The epoxy resin would have taken too long to cure and be ready, and there would be no time to polish it properly for a clear finish.

1. Bandsaw - rough cutting slab in half edgewise, lengthwise
2. Router - hand held for freeform lines
3. Tablesaw
4. Clamps
5. Router bits - 1/4" diam flat end mill
6. Rotary Sander - super helpful for flat areas
7. Sand Paper - a ton of it
8. Wood block for sand paper
9. Glue
10. Staple gun, straight staple pins - optional, but can be useful
11. Danish oil
12. Rags
13. Toothbrush
14. Gloves

I don't have photos of this step - but this requires a hefty roughcut bandsaw and a whole lot of care while pushing the slab through.

We reduced the 2" slab down to about 1" per slab. This cut is best done with a VERY hearty bandsaw with a thick blade (about 1" wide). Cut slowly, and don't rush the wood, otherwise, burn marks will appear.

From one whole slab, we ended up with two thinner ones. One thin slab would be the back of the chair; the other would have the seat and two legs and any leftovers would assist as supports underneath and connection dowels.

If your slab can fit into your planer, I'd recommend planing the whole thing - it will make life easier when you're routing the contour lines.

The back of the chair was simple enough - contour lines across the entire slab. Adobe Illustrator was used to create the SVG file to send to VCarve for the Shopbot Alpha CNC. The lines were traced over the (locked) photo layer onto the drawing layer in Illustrator.

The seat and legs, however, needed to fit the criteria for sitting and height of seat. Since the seat thickness would be about 1", the legs could be at least 17", but we added a bit more as we wanted to tilt the legs a bit for more stability.

The seat width came out to whatever the slab width was (14"), with an added tenon to go into the chair back slot cut by the CNC / router.

NOTE: The mortise slot at the chair back for the seat tenon was routed AFTER the back was assembled with dowels at three points where the slabs' live edges came closest together.

Dowel centering devices can be used to pinpoint where dowel holes need to be drilled. Be sure to drill in the same direction through for both holes (if one is tilted, then the dowels and parts won't slide in properly or at all!). Dry fit to test before gluing.

If you wish to contour the seat top, use the 2.5 / 3 D profile in VCarve, and surface file it. Manually, the seat can be contoured with lots of sanding, or careful routing - since we didn't do this, there are other methods, too. Please add to this in the comments.

The contour lines were traced in Adobe Illustrator from an actual photo of some Antelope Valley photos, and imported it into the VCarve application to indicate the pathlines for the CNC. In VCarve, there are two different toolpaths: engraving contours, and through cut with tabs. Tabs are important to prevent pieces from flying after the final through cut! It's kind of cool to watch the video replay of the toolpaths - it also allows you to see if anything needs adjusting before sending the router to REALLY do it's job.

NOTE: If you're going to CNC the seat, use the 2.5D or 3D contour, not the 2D contour. This choice accommodates for a smoother transition, and definitely use a final toolpass for a finish to smooth out the jaggies from the rough cuts.

Without a CNC, you can hand draw the lines or project the lines to the wood and draw in the lines. If your surfacer is smooth, this is easy to do. For the seat contour, grinding down and sanding will allow you to hand-shape the final contour.

Follow the lines with your router - we used a 1/4" flat end mill for the channels.

Since we could not drill into the wood for supporting onto the CNC bed, we came up with clever ways of clamping the slab down as the CNC worked on one part of the slab. After that part was finished, the slab was clamped down where the lines were already routed, and the next part was cut.

Our design figured the curvy contour lines were "Nature." We also considered Man to be part of Nature, so we included a straight line down the mid-section of the slab to represent Man. Our aim was to put the live edges together and have the straight edges outside.

After the CNCing of all the parts, one chair leg and the seat got stolen with a bag of bananas. Our project could not be completed in time. We had to remake those missing parts, and present at a later date, while continuing to work on current and the CNC project.

Making dowels was more fun than I thought it would be!

Our university woodshop happened to have an old fashioned dowel-turning jig that looked like large pencil sharpeners, crank and all. I'm sorry to not have a photo of the process as it's rather unique. There were several sized dowel diameter sharpeners to use, and turning a square-ish stick into a round stick is pretty amazing. Plus, we got to use up any scrap wood leftovers from the slab!

I did manage recently to make a DIY dowel-making jig with old bandsaw blades and scrap wood. Here is a Youtube on a similar method to make the jig with three blades. I used two old saw blades but three would have been better for making smoother surfaced dowels. For the youtube start around 6:26 (https://www.youtube.com/watch?v=PkS6wHRGyvM).

BTW - it's easy to go down a rabbit hole in learning dowel-making jigs!

After the CNC pieces were cut out, it was time for sanding the pieces. They were laid out to dry fit for the dowel connections. This was one of the toughest parts to do as the live edges are - gosh! - not level to drill into! Somehow the holes were made on both side of the live edge gaps - preferrably where the parts would touch and not have the dowels show. Hiding the mechanics of assembly is key!

The next hard parts were the legs as they're canted at a slight angle for stability, but clamping them was a challenge due to the angles. The photo does it no justice to show how tensegrity tenuous the clamping was!

The parts were fitted and dowel-glued together, Japanese sawed or ground down the dowels, as needed, contoured the added support pieces, and final sanded. To ensure strength, the chair was allowed to dry for over a week.

A final sanding at 220 grit allowed any staining to seep into the wood. Danish Oil, clear was used to coat the sanded wood. This is the most satisfying point of a wood project - watching the beauty of the grain pop out from the muted sanded wood when the stain coats it. Two coats were applied, wiped down with a clean rag, and dried. Light 400 grit sanding was applied between coats.

Post-assembly, the toothbrush came in handy for getting out any loose sawdust and debris in the channels and tight spots.

Stand back and bask in the glow of a well-made chair.

Though spindly legged and thin, the chairs suprised all with how sturdy they turned out to be as well as lightweight. They're easy to move around and carry. Game of Thrones came to mind with the unique shaped chairs. We had purchased two large slabs and were planning to make (4) dining chairs total before a seat and leg were stolen in the beginning of the project. In all, we made (3) dining chairs. I have (2) of them.

Though we did not use epoxy resin, which would have added weight, time and work, the chairs seem to make a statement - a very natural one!

To do this project again, I would definitely plane the two parts as soon as I could. Since we had the straight cut separating the pieces, it would have easily fit the planer. But, that would require even more clamping challenges to cut the contours. As each slab is a different shape, the VCarve cutting paths would need to be adjusted.

Or, the CNC could have surfaced it level at the beginning of the project.

It was a great Furniture Design challenge. I've since made more furniture with slabs and it's very satisfying working with the Live Edge.

The photos shown are of a "Bacon Table"