Stair Tread Arm Chair - Building Plans

Sunday, March 10, 2019 -
How to build a sleek and modern arm chair from just 3 off-the-shelf stair treads using FREE building plans and a video tutorial

*This post is sponsored by Kreg Tool. I have been compensated for my time and provided with product or payment in exchange. All opinions are my own. This post contains affiliate links. 

So building chairs is scary. There are so many factors you have to keep in mind, like angles and balance, which don't come to play with straight forward builds like tables and even beds. If a chair isn't the right height it doesn't function and if the back isn't angled properly, it becomes uncomfortable to use. 

I actually built a wood and leather sling chair like 5 years ago (which has been sitting in my back yard and is miraculously still holding together), but sling chairs don't have to take into account all those tricky factors. The seat I normally use to put my shoes on everyday broke recently, so I decided it was time to woman-up and tackle a modern arm chair build. 

Materials List:


Cut List:

* Laminate (glue long edges together) 2 of the stair treads together, making a 48" x 23" solid wood panel before making cuts. Dowels, biscuits, or other joint enforcement can be used but isn't necessary. 

  • (1) 20" x 20-1/4" x 1"
  • (1) 20" x 18" x 1" (cut one 20" edge 15 degrees off square)
  • (1) 8" x 22" x 1"
  • (2) 8" x 20-1/4" x 1"
  • (4) 2" x 23-3/8" x 1" (cut into a parallelogram, 10 degrees off square)
  • (4) 2" x 16-1/4" x 1" (cut into a parallelogram, 10 degrees off square)
  • (2) 2" x 12-3/8" x 1" (trapezoid, measured long point to long point)
  • (2) 2" x 20" x 1" (bevel entire lengths of both long sides at 10 degrees of square)

You might be looking at the materials lists and see that I am calling for 1" thick material. Not the common "1X" material that I usually use and is actually 3/4" thick. Not only does the extra 33% of material add a lot of needed strength to a structural build like this, I think the non-standard thickness makes the chair look custom built. Like you spent hours upon hours milling rough sawn boards and hand cutting joinery. 

Don't freak out! I found an inexpensive and easily accessible source for 1" thick boards - STAIR TREADS! Yep. I picked up 3 off-the-shelf pine stair treads from Home Depot for around $12 each. They come with a full round-over bullnose on one edge which can be cut off, but I actually decided I loved the look and chose to work it into the design. 

Making lots of long rips and angled cuts sounds intimidating - I get it. Also, those kinds of cuts usually require more heavy-duty tools to produce accurately. That's why I chose to try out a whole new cutting system from Kreg Tool

Kreg just launched the Adaptive Cutting System, and it's awesome! The ACS is a collection which includes a portable project table, a precise cutting track, and several measuring and referencing attachments. The system even introduces us to Kreg's first power tool - a super accurate plunge saw!

So far I haven't found a cut that I haven't been able to make with the Adaptive Cutting System. If you're interested in learning more about all the bells and whistles (and they are freaking awesome!), I recommend watching this release video.

And make sure you check out my chair build video above to see how versatile the ACS is! And if you don't have a system for yourself yet, don't fret! I designed the plans to work entirely with a circular saw as well! 

 Leg Assemblies 

1. Connect pairs of legs together using leg stretchers. Secure in place using glue and 1-1/2" screws through 1"  pocket holes.

2. Align the inner leg supports on the inside of leg assemblies, flush to bottom edge. Attach in place using wood glue and 1-1/2" brads driven from the inside face.

3. Connect the leg assemblies together with horizontal front and back stretchers. Secure in place using glue and 1-1/2" screws through 1" pocket holes. 

Seat Assembly

4. Join both 8" x 20-1/4" seat sides to the back rail, flush to outer edges, using dowels and wood glue. 

5. Place the seat bottom flush to the lower edge of both seat sides and back rail. Apply glue to adjoining faces. Attach in place using 1-1/2" screws through 1" pocket holes. 

6. Cut bottom edge of seat back at a 15 degree bevel. 

7. Place the seat back between seat sides. Tilt at 15 degree angle between bottom and back. Apply glue to the adjoining faces. Pre-drill from under side of seat. Secure in place using 2" screws.

Connecting Seat and Legs

If you are wanting to copy the full radius round-over look like I did on my chair, this is when you would want to add it to all the parts. Use a trim router and 1/2" round-over router bit to round the sharp edges on the seat sides, back, as well as all the edges of the legs.

 I recommend taking multiple passes, only removing 1/8-1/4" of material each time. It's much safer (more control) and helps to avoid chip out. 

8. Once the edges are shaped how you'd like, place the seat assembly between legs, resting on inner leg supports.

9. Pre-drill through seat and into leg assembly. Attach using 1-1/4" screws. Counter sink the screw heads and plug holes with dowels. 

Sand, apply finish of your choice and that's it! You've got one solid place to sit and tie your shoes. 

Although I think this design would totally work with sharp, square edges. I am really happy I chose to round over the edges. It's kinda a nod back to the fact the wood came from the bull-nosed stair treads.

I know most of us don't think pine is the most beautiful wood. I'll admit, I myself get flashes of 1990's cabin when I see too much knotty pine

Luckily, I was able to counteract the typical golden color pine gets when it's sealed with a little tweaking to my Polycrylic top coat. I talk more about the finish in the build video, so make sure to check that out.

I tackled my fears and I have to be honest, building a chair wasn't nearly as hard as I thought it would be. The ACS was super precise and made it easy to make all those tricky cuts. You can expect to see it used in many of my future builds.

What do you think? Ready to take on a chair build yourself? Pin the image below to save the idea for later, and if you have any additional questions about the Kreg Adaptive Cutting System, make sure to leave a comment!

how to build modern mid-century minimal easy simple wood arm chair seat video tutorial

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