Attic Stairs - Part 1

This is a project I have been delaying the start for some time, partly because it has taken me some time to come up with a design I liked and partly because I have not built many stairs. I eventually settled on a spiral stair design with each tread extending to a supporting wall. As a results each tread is a different shape. 

The total rise for the stairs is 2730mm, which gives me 13 steps with a rise of 210mm. I set the nominal tread angle at 25.7º and the minimum clear width of 770mm extending to 1200mm on the widest step. To repeatedly cut accurate treads I created a plywood tread template. The template greatly speeds up laying out cuts and minimising waste.

Each tread is cut from 24mm furniture grade plywood. At the centre of the spiral stairs is a 120mm diameter column also made from a sandwich of plywood circles turned on a lathe (I'll write up another post on how I made these columns). The front edge of each tread has a reverse curve which I cut out with a pattern cutting router bit. The reverse curve on the front edge helps maximise the step going. The going near the middle column is 90mm and the centre going on the narrowest step is 250mm.

The steps have a closed riser design made from 12mm plywood. The bottom of the riser fits into a routed channel on the top of each tread and is secured with screws from the underside. The top of the riser fits into a channel on the underside of the next step and is left to float in the channel. The central column of the stairs is aligned and secured in place with a 3m length of 20mm diameter steel conduit.

I started this job over the Christmas holidays and managed to complete 4 steps over the holidays. Cutting the treads and turning the central columns is reasonably quick. Finishing the parts is time consuming with 3 coats of Dulux Diamond Glaze varnish with 8 hours between coats. Securing each step to the nearest wall also takes time as I need to make sure each step is level and there is no unnecessary movement on the steps. Over the next few weeks I hope to add the remaining steps and finally have easy access to the attic conversion.