There are a couple of wonderful sources to consult on building circular stair railings. One is Volume 5 of the Foxfire series, which contains great stuff on smithing in general, as well as iron making and gunsmithing of flintlocks. In that last section about guns is a run-down on how to make a rifling guide that saved my bacon 20 years ago when I had to make a railing for a circular stairway.

The solution one old codger down in Georgia had devised was as simple as it was elegant. He drew a line on the floor that represented the barrel length. On that barrel line he marked the distance he wanted his rifling to travel in making a full diagonal traverse of the inside of the barrel, i.e. a full circle. From that point he marked another point, perpendicular to it, at a distance that was exactly the circumference of the barrel. He connected the end of the barrel line to that last point with a chalk line. Rolling a dowel of the same circumference as the inside of his barrel down across the chalk line, and carefully keeping the dowel parallel with the barrel line, he wound up with the chalk line marking the precise spiral he needed for his jig.

In other words, the gun maker showed me how to open up the cylinder of my spiral staircase and get the pitch and length of the railing I had to forge.

I did not make a full-scale model of the staircase, but working from architect's blueprints of the house, and laying out with an architect's scale the vertical distance from the bottom floor to the top gave me one leg of the triangle, and the sum of the horizontal distances from the bottom of the first riser to the top of the top riser gave me horizontal leg. Connecting the two gave me the hypotenuse the length of my railing minus the overhang required by the code and the decorative finial scrolls.

I made a partial cylinder of 1/4 inch plate a couple of feet long with the same radius as the staircase would occupy and as high as three risers and treads. To it I welded L-shaped prongs that matched the points on the pitch the rail would have to hit to match the pitch of the stairs. This jig made it possible to heat the railing, = by 2-inch flat stock, and bend it in eight inch or so heats to the proper curve and rise while keeping the flat plane from twisting out of level. I forged the railing in sections of about six feet, and arc welded them together as I installed it.

It would have been much easier to make the railing out of round stock, with no need to worry about keeping the flat plane level.

Things to be careful about with railings are many. The Uniform Building Code may not apply in your area exactly as written in the book, so be sure to check. In fact, there may be no building code at all where the job is going to be installed - but you will definitely have liability just the same, so it makes sense to abide by it.

The code is quite specific about the size of the handrail, how far out from the wall it is mounted, how far above the treads of the stairs it must be, and-- NOTE THIS CAREFULLY- how far it projects on a horizontal plane from the top and bottom risers.

If the railing has balusters, make sure they and any other elements in your design -- are no farther apart than four inches. This is to keep kids from having a terrible accident, getting their heads stuck and perhaps breaking their necks or strangling.

If you buy ready-made elements, like mounting brackets, balusters, decorative elements, cap rail or finials from a supplier, read the catalog carefully to make sure you know what you are ordering.

Cap rail is steel, and can be welded and bent, both the easy and the hard ways, without a bender, with a jig like the one described above, and looks great when it's done and painted. But finials are often cast iron, and getting a solid union can be an adventure.

Also, beware that some of the ready-made finials, especially flat volutes, may not pass inspection: that fancy inside curve can snag a finger or a ring and the inspector may demand you weld in a filler piece.

Do not- (i.e.,NEVER) -- let anybody else mount your brackets if the railing is going on a wall, and let nobody else, ever, position your newel posts. They must be positioned exactly in the same spot relative to the treads they are above or the railing will wander off the proper pitch vis a vis the stairs.

Be especially on the lookout for buried electric wires and plumbing pipes.

If you use arc, make it 7018. Check every cast iron weld carefully for hairline cracks. Have a plan on paper approved and signed by your client, with liability for such surprises and the design in general clearly established. You've got quite enough on your hands with liability for the workmanship.

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