Spiral Stairways:

Commentary on designing, building and quoting on wrought iron spiral staircases.

A friend of mine has built two spiral staircases with all hand forged pickets, treads, risers and one piece top rail. He's very picky about his work and his customers got a LOT more than they paid for. While building both staircases he swore he would find a way to heat the entire top rail and bend it at one time. There were dreams of building a small rolling mill and spiraling the rail as it came off his pipe dream. . .

  • First, the design must meet building codes.
  • Then accurate elevation dimensions must be known.
  • Forget what the builder says it will be. It will always be an inch or more different than the drawings.
  • You will need as builts OR a $$$ built in for errors.
  • You will probably need a couple meetings with Architect and clear understanding of the fit and schedule.

How the blooming thing will be installed is a REAL problem. The geometry of a spiral staircase dictates it will be 16 to 20 feet tall and at least 5 feet in diameter! Even with a large window removed it may not be able to fed through the hole in the floor! Placement by crane before the roof is completed is just about the only option. This means YOU have to be ahead of schedule delivering the thing or leave the country!


First you kill a chicken. . . Whoops, wrong recipe.

First you need a center column. 4" pipe is normally used. The schedule (wall thickness) to be determined by the Architect or Engineer. We dreamed of using a square tube twisted into the correct spiral.

Then you need to make the treads and their supporting bracketry. For uniformity this requires a number of fixtures. If you want to rivet the attachment points be sure your design requires rivets 180 degrees from each other. That way you use a piece of bar (long rivet) all the way through the pipe. For spacing, mins, max's and such see the building code and Architectural Graphic Standards (or pay a C.E. for specs). Wood treads on iron bracketry works nicely.

The treads should be carefully installed first. Fixturing and accurate layout are a must.

Pickets are pickets in a straight line or a circle.

The top rail is a bitch. Forge at least one end first. IF you have a heavy enough set of rolls or tire bender this can be a start.

The radius is that of a circle the diameter of a straight line at the same rise and run as the outside of the treads across the diameter of the stairs.

(IF you don't understand the geometry implied you had better forget this project).

Plan on heating the top rail a couple feet at a time with BIG rose bud torches as you fit it to the stairs. Getting it to lay flat (perpendicular to the pickets) is tough. BIG wrenches, scrolling forks and swage blocks come in handy.

After prebending, the top rail assembly starts at the bottom and progresses up the stairs. This requires space and manpower:

  • A torch holder
  • A riveter or backer upper
  • A worker that can hold an anvil unsupported . . .
  • someone to steady the thing
Meanwhile you will be rolling and humping this monster around and around and around. You will never see the thing vertical until after it is finished (unless you have one HECK of a shop).

A genuinely rewarding experience.

I could get into more details of design but every shop should design around their capabilities and facilities.


Figure what you THINK the job is worth then double of triple the price! You might make a little profit that way.

The stair can be designed to break down in smaller units for installation but this adds to the cost. A joint in the center post must be as good as welded and not look like a joint (a very hard thing to hide).

If wood treads are used they should be installed AFTER the unit is in place. Good design practice is to use thicker than needed landing treads so that they can be planed or sanded to equal the surrounding floor.

The top rail should be solid. If its to be a custom rail you will need a 300# or up hammer to forge top rail. Treads can be connected to one and other with the pickets. Joints between the top rail and the pickets should be substantial, as the top rail actually supports some of the load.

AXIOM: All steel is like rubber except when opposed to flesh. -guru


Its a lot of work but I've seen it pay off on other complex rails. Build a mock-up to fit the rail. As a spiral staircase is (mostly) repetitive only a short section would need to be built, say five feet. Starting with a short center column bar stock of equal length would be welded on to produce the spiral, then diagonal braces attached while correcting errors. Then two pieces of flat stock would be formed to fit and welded on the outside of the corner to produce an angle cross section.

Forge the termination, roll and stretch your rail to a rough spiral. Then starting at the finished end clamp (tons of clamps) heat and fit the rail to the fixture. If you don't have them you had better budget a few dozen or more heavy clamps for this project. When the rail fits that short section slide it down about half the fitted length and continue the fitting process. It should take a day or two to build the mock-up (not including scrounging materials) and a day to do the fit (not including the trip to refill the gas cylinders).

When you are finished the best you can expect is +/- 1/2 foot on the length, but maybe +/- 1/2 inch on the spiral (ignoring a little spring back).

On big heating jobs like this I found a propane/oxygen torch to work quite better than oxyacetylene. You need a big commercial propane tank (250#). The advantage of the big propane tank is that it will feed a rosebud while you must gang up several acetylene tanks on a manifold.

A propane/oxygen rosebud is much quieter and gentler than the oxyacetylene. With big oxyacetylene rosebuds I always felt like I was holding onto an out of control rocket! Victor makes propane tips for cutting, heating and welding that fit their standard torch (and YES they ARE different).

A tool that will pay for itself if you are using a rosebud a lot (or production brazing. . .) is an automatic torch shutoff and pilot (called an "economizer valve"). This device has a lever that when you set the torch on it shuts off both gases. It has a little wind resistant pilot flame so that when you pick up the torch you automatically get a relight! The great thing about using one of these with a rosebud is that when you sit the torch down for a minute you don't worry about setting something on fire.

ON LAYOUT AND FIT by Cracked Anvil

In making making a rail for a spiral stairway what you are doing is, you are wrapping the long side, the hypotenuse, of a right triangle around a cylinder. The hypotenuse is the rail. The diameter of the cylinder you are wrapping the rail around around is the diameter of the circular stair in plan view (minus the distance the rail sits away from the wall if there is a wall around it). The height of the cylinder you are wrapping around is distance from finished floor to finished floor. You just lift the cylinder up to railing height.

Now comes the tricky part: check the number of treads. Multiply that by the tread width at the outside edge -- do not include any overlap of the noses. You want just the horizontal distance covered by each tread, starting where the one beneath ends. Add them up and you've got the bottom leg of the triangle. Lay that out square to the height and then connect the two ends and you have the basic length of the outer rail (except for code-required stickout--see below) and the rise, too, the pitch, the angle at which the rail goes up.

Now build yourself a jig:

  • Find a section, partial is okay, of hefty -- because you are going to be doing a lot of bending against it-- pipe or cylinder of maybe 1/4-inch or 3/16 plate close to the diameter of your stair.
  • Now weld some L-shaped anchor points onto the curved plate. These should be at least 1/2-inch round, stock bent into Ls just a smidgeon bigger than the width of the rail, positioned at the same rise-angle relative to the long axis of the piece of cylinder as the rail is to the floor.
  • Heat the rail stock and bend it, pulling against the anchor points, to fit the curve of the jig.
It'll be close enough. Note: you will save yourself a lot of grief if you can use round stock for the rail. With round, you will not have to try to keep a flat rail flat as it curves and rises at the same time.

Do the same layout process for the inside rail. The rise is exactly the same. You just wrap it tighter, around the smaller cylinder representing the distance the inner rail sits from the center of the circular stair. Do not forget to allow for the horizontal stickout past the top and bottom treads that is probably required by your code as it is by the Uniform Building Code, which calls for 12 inches past top and bottom risers. On the install, be extremely careful in measuring for and mounting anchor points on the wall if the rail is wall-mounted-- or on the treads if the rail is free-standing with balusters-- to go in same distance from each tread nose. Otherwise, when you plumb up from them, if you are not plumbing from points the exact same distance on each one, or setting the balusters at the same distance in, the pitch of the rail will be wayyyy off, will not follow the stairs.

Balusters cannot be farther apart than 4-inches max. UBC sez stair rail must be 34-to-38 inches high (guard rails are minimum 42"), 1 1/2 minimum to wall, 1 1/4-to-2-inches in cross-section.

Go for it!

Cracked Anvil -- 08/13/01 15:00:16 GMT


As you can tell from the previous posts about building using only classic Blacksmith OR modern fabrication techniques, spiral staircases are a technically challenging job. In fact, from an engineering standpoint they are a most difficult structure to analyze. Assembly requires careful planning, logic and closely meeting dimensions. Estimating these jobs are more difficult than any other and it seems everyone looses their shirt on their first one (or every one).

If you have enough architectural work coming into your shop, try selling a small quarter turn stair instead of a straight railing job. This is an opportunistic job that require cooperation from the Architect, but it will give you some experience.

My opinion - From a mechanical standpoint, if you can not make your own design layouts and plans (including mathematics) of a spiral staircase you have no business trying to build one. From an artistic stand point you may have all the Blacksmithing skills but this is only about 20% of what's needed to built a spiral stair case.

Think about it. You will know.

-- guru

References and Links

  • Alphabet Soup What's that acronym?
  • BOCA The Building Codes People
  • NOMMANational Ornamental and Miscellaneous Metal Associaltion

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