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11 November 2011

How do the Genius spiral stairs wooden handrail pieces make a helix if the tread rise is variable.

A highly technical question from a deep thinking gentleman.

This gentleman has spotted what the mathematicians amongst can see is a flaw in the geometry of making a helical wooden handrail for variable height kit spiral staircases out of short wooden sections. This is exactly what happens on spiral stairs kits such as the up market Genius range. However the manufacturer is on the case and has an answer for this problem.

Let me first explain the problem. A spiral staircase handrail forms a helix just like the spring on your pogo stick. To form this out of real wood is an expensive process requiring curves in two directions. It goes round in a circle on plan, the circle being the same diameter as the spiral stair. It also has to climb from the bottom to the top stair tread which is the second curve. OK all of this is possible but the helix will vary with every diameter and with every height. Therefore you have to make purpose designed helix for every stair. All kit spiral stairs like the Genius range require you to be able to change the height of spiral stair. Without this variability you would no longer have off the shelf kits, but would have to pay a lot more for a spiral staircase made specifically for your floor-to-floor height and diameter.

There is a further problem with kit spiral stair helical handrails, they are not only difficult and expensive to make, they are also big, awkward and very expensive to transport in one piece. So having made a helical spiral stair handrail the manufacturer cuts it into shorter lengths so that it can be packed in crate and transported. This process also requires the design of a method of rejoining the pieces together.

So the problem is how to make spiral staircase handrails that go round in a circle of a certain diameter but also curve in another direction to allow for various heights. The first curve is easy you just make a set handrails to suit the various diameters that you supply the stairs in, lets say four diameters. So each diameter spiral stair has its own handrail. The second curve is much more difficult. The only real solution is to also make a handrail not only for each diameter but for each millimetre of height of the stair height range. This is practically impossible as it would require the manufacture of thousands of variables. Failure to do this however means that the handrails will climb the spiral stair at a different angle of pitch to the stair treads, so it will get higher or lower in relation to the treads.

So the solution to this problem lies in the way that the handrail sections are joined. Instead of making the join between two handrail sections butt up hard against each other which would fix the angle of the second curve, the clever manufacturer supplies a clear tapered washer that fits between the two sections. By rotating the washer you can vary the angle of pitch a little on each join. This solves the problem, it is not a perfect solution but it works, and if you take your time with the washer adjustment you will achieve as near a perfect result as makes no difference. Unfortunately it does require you to align it by eye and tape measure as it would be nigh on impossible to produce any kind of tables that would help with this. Trust me it does work, I have seen Genius spiral stair handrails that have been assembled by people who were totally oblivious to the function of the tapered washer and just inserted them any which way. The result looked fine even to my highly critical eye. So worry ye not my mathematical friend the circle can be squared, or near enough anyway.

The Spiral Staircase Doctor