I’ve been working on a spiral staircase recently and not a small one either. It was for a fuel tank, 60 plus metres across and 14m high. It allowed me to practice using the helical curve command so I thought I might share a smaller version here.
You can see I’ve already got my centre pole and treads, patterned using one helical curve (done in an earlier tip). Now for the handrail. Handrails are typically 1000mm above the nosing so I prepare my construction sketch first. The vertical line length tells the Helical Curve command how far the curve will rise aswell as the axis or rotation.
Start the Helical curve command, define your axis of rotation, then choose the start point. Make sure the direction arrow points the correct way. Define your pitch (the distance between complete turns) and the number (or fraction) of turns.
Finally I used a simple Sweep command with Plane Normal to Curve option to define the handrail. To finish the job I just need to place the support posts.
Your manufacturer will need to know the total length of material, the radius of the centre of the handrail and the pitch. You can use the 3D measure command to find the total length of material.