True Radius Calculation for a spiral

[donw1492]

How do you determine the true radius of a spiral staircase hand rail in order to form the handrail?

 

[dvd]

Here is how I have done it before.

If your staircase turns, say, 270° you need to calculate the length of handrail first. This will be the hypotenuse of a right triangle which has:

run=2*pi*(handrail centerline radius)*270°/360°
set=height from landing to landing or floor to floor

handrail length = square root(run^2+set^2)
(allow a couple of feet extra at each end)

Roll the pipe at:

true radius=(handrail length*360°)/(2*pi*270°)
(use the length calculated above not your total length)

After rolling to true radius (which with the extra added on will be somewhat more than 270°) you need to put a comealong on one end and clamp opposite end and pull vertically until you get the landing-to-landing height. Don't include the extra when measuring this height. Try to position your comealong and clamp so that you pull at the 270° position when viewed from above.

Try it with a piece of wire first at a smaller scale.

Let me know if you don't follow this.

 

[donw1492]

Thanks, I follow OK. My problem was a 12 foot spiral staircase with 16 steps. Worked out to a true radius of 3.412 ft. for a 3 foot stair radius.