They say a job well planned is half done.   I started laying out a curved stairway today and thought I would post just a little of what has to go through my mind laying one out.  

My client wanted as much room as possible between his fron door and the starting step of the curved stairway.  This stairs had a 134 inch outside radius and the face of the inside skirtboards radius is 84.375 inches.   The minimum run measured in 12 inches from the skirt face has a radius of 96.375 inches.  At this point…..the run cannot be less than 10.00 inches.  So…to give the client his max clearance to the door….I had to give him the minimum walking line run of 10.00 inches.  This stair has 17 treads.

The way I compute this is to take the 96.375 inch radius walking line and figure its circumference.   2  X  96.375  X   pi……gives a curcumference of  605.541984170 inches.   Bear with me on using all the decimals as these are needed for the final result.

Next I set up a ratio ..       605.541984170 inches  is to 360 degrees as 170 inches is to X.

Note:     170 is the run of 17 treads at this 10.00 minimum per tread….

Cross multiplying….you end up with 61200….and then working the ratio….you divide 61200 by 605.541984170 to get 101.0664853 degrees of swing for 17 treads.   Dividing this by 17 arrives at 5.945087368 degrees per tread.

Now….I always double check myself so to do so here…I divided the walking line circumference of 605.541984170 inches by 360 degrees to get 1.682061067 inches per degree.

Now….the fun part.   Multiplying this 1.682061067 inches per degree  by 5.945087368 degrees……arrives at 10.0000000 inches.  Time to go build my stairway…..I am now half done…..NOT    <G>

Anyway….thought I would share just a little of what makes me wacky….Here are some pictures of the 2d layout on the shop floor awaiting a full scale 3d stairway to rise vertically.