How to make curved stairs with a central cut string

This is an article that is not really about stair software but a visitor on my blog asked about making curved stairs. I have developed several techniques for different types of curved parts, cut strings, closed strings and handrails according to whether they are flattish, molded round etc.

Here’s the way I make a curved central cut string.

Note that although StairDesigner helped me set up the general lay out, the working drawings were drafted by opening the StairDesigner DXF files in Autocad.

Most of my curved strings are built using a technique I developed that I’ve called laminated layers. In fact to get the curved helical shape I glue together curved horizontal parts cut and calibrated from a flat board.

Here’s a photo of the cutting and calibrating the curved parts.

These parts are drilled and dowels used to reinforce the laminated assembly and stop slippage while gluing.

Note how I use the calibration template to precisely position the holes.

This photo shows how I glue the layers together using the dowels and template to align them.

For convenience I glue the parts together in blocks that are the height of one rise, and then assemble the blocks. This enables me to cut the helical under side with a saber saw.

I then assemble the blocks on a floor plan making sure everything is lined up with a laser plumb line.

Once the string assembled I glue  laminates on the layers to give the  string it’s finish.  To glue the face laminates I use some special clamps.

This stair goes up into a circular stair well, here’s the stair well assembled inthe workshop:

Here’s the curved string with the stair well assembled in the workshop:

And here’s the stair assembled with it’s center post and steps in the workshop:

And from underneath:

Here’s the stair installed in the clients bedroom.

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