I made this spiral staircase for my loft in Boston. I used my X-Carve CNC machine by Inventables.com to cut out the initial pieces. In the interest of time I had a friend use his machine which has a large bed cut out some of the pieces. Each step is made out of 12 layers of ¾” furniture grade plywood. You can download the dwg drawings that we used here.

The stair case is 16 and ¾ steps tall and is built around a 3” schedule 40 steel pipe. The steps are the same but each one is rotated 30 degrees with 12 steps creates a full revolution around the pole. I mistakenly assumed that the ¾” plywood I was using was was exactly ¾” thick and my steps ended up being about half an inch shorter than I intended but it all worked out. I thought that keeping the stairs aligned was going to be a bigger challenge than it was so I had the CNC drill perfectly aligned holes for ½” dowels. I ended up not using these holes since it was easy enough to just to align the edges and clamp the boards.

This project costs around $900 and takes about 40 hours to build.

SUPPLIES:

¾” Purebond Plywood
Available at the Home Depot
I used purebond plywood because I didn’t want typical plywood off-gassing formeldyhyde into my loft.

Finish screws
Available at the Home Depot
I used finish screws ranging in length from 1 5/8” to 6 ½”.

Wood glue
Available at Home Depot
I used high strength wood glue to help laminate the layers together.

TOOLS:

RYOBI ONE+ 18 Volt Cordless Drill
Available at Home Depot











X-Carve
Available at Inventables.com

INSTRUCTIONS:

STEP 1: The foundation
I made sure to reinforce the floor with LVL beams that could take the load of the staircase. This added to the construction cost of the building but I would have needed it even if I went with a conventional prefab steel spiral staircase. I had some 3” diameter schedule 40 steel pipe welded to a piece of ½” steel plate. We then used long lag screws to screw the plate to the LVL beams. At the top of the pole there are two steel arms that connect to the wall.



STEP 2: Cut the pieces
I used my X-Carve to cut some of the initial pieces but due to the small size of the bed and the quantity of pieces I had a friend help me using his machine which has a larger bed. The X-Carve actually cut cleaner than the larger machine but the large bed size let us lay out the pieces more efficiently.







STEP 3: Start the first one
The steel plate at the base is ½” thick so I had to plane down an extra piece and cut off the head to fill in the gap. I then used construction adhesive to glue it to the floor before using long finish screws to fasten it in place. I then used wood glue to place the next few 2 layers and used lots of screws to make sure that the foundation of the stair was firmly screwed to the floor.









STEP 4: One layer at a time
Originally I intended on pre assembling each step by itself and then placing them around the pole but the puzzle joints between the pieces of plywood were too tight so I had to assemble it layer by layer around the pole. I used construction adhesive to fill in the 1/8” or so gap between the steel pole and the plywood. I used wood glue between the layers of plywood. I used about 9-12 finish 2”-5” long finish screws to fasten layers. I had to alternate the screw patterns. I used my body weight and clamps to press the layers firmly together before screwing them. It took me about 2 hours per step.















STEP 5: Make the landing
Once I got to the top step I cut pieces of plywood to match the profile of the top step. I had to use my fig saw to cut a piece out to fit around the pole. I glued to layers of plywood together and clamped them to make the landing bridge.









STEP 6: Install the landing
I built up the sill of the door a bit to make sure I had enough clearance under the bridge. I then placed the bridge to see if it fit and screwed in plywood pieces on either side of it. I then removed the bridge and painted the underside with a personal reminder. I glued and screwed it in place.















STEP 7: Reinforce the stairs
The stairs are rock solid and didn’t wiggle or creak at all but just to be safe I drove 5” long screws in the points that had the least amount of plywood overlapping.





STEP 8: Wood putty the screw heads
I used wood putty to cover the heads of the screws and then sanded it flush once it was dry.





STEP 9: Sand, sand and sand
I sanded the stair case with an orbital sander and belt sander first. I used a sanding sponge and a detail sander to do the undersides.









STEP 10: Finish
I finished the staircase with 2 coats of miniwax polycrylic.



What about a railing?
I am still working on the railing and will post a video of it when I am done.

Design Notes:
I was inspired by a staircase I saw at the Boston Society of Architects by Matter Design Studio but my staircase does have many similarities to the staircases designed by Tron Meyer which is incredibly well-crafted and detailed by Rupert Lees whose staircase has a more sophisticated form.

Thanks for checking out my CNCed Spiral Staircase!

Disclaimer!

This was an experimental project for my own private use and I make no claims about it being safe or suitable.

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