Editing a curved string stair in Autocad

This article follows the article “Stair Design for curved strings and landings” and shows how to use the Stair Designer 2D DXF file in AutoCAD to modify the original design and draw the shape of the curved former and laminates used to make the curved strings and handrails.

To build the curved strings and handrails for this stair I have used a laminated technique where I press a packet of thin laminates onto a form or mould that gives the final curved shape.

I had the choice of using either this traditional laminate construction or my own horizontal laminated construction that I use for central cut strings that doesn’t require the building of a form. Both techniques are suitable for building this stair but due to high number of curved parts (a total of 16) in this project, I opted for building a form and using vertical laminates.

To make a 51mm thick string and handrail, this technique requires the building of a form and uses packets of 7 layers of 7mm bendable plywood with 2 outer layers of 2mm oak veneers.

Here’s a photo of the pack of laminates ready for gluing  and placing on the form.

Pack of laminates ready to be placed on form

Pack of laminates ready to be placed on form

The form is  built with 30mm ply shapes and 60x50mm pin framing. 8mm bolts are used to pull down the packet of laminates onto the form.

Here we see a part of the handrail being pressed into shape.

Form for laminating stringers

Form for laminating stringers

The curved string will be jointed using bolted croched joints.

Here’s a photo of the finished string standing in the workshop :

lim-1v04


Here’s a photo of the bolted joints assembled on the back side of the string:

Croch joint bolted on the back side of the stringer

Croch joint bolted on the back side of the stringer

Once the laminates are drawn in Autocad I print out each section full size and use the prints as templates to rough cut and mark out the strings:

shape of the laminates in Autocad

shape of the laminates in Autocad

Here’s a photo of the string coming off the form ready to be marked up with the full size template:

String with template

String with template

And a photo of the curve part with the joints and edges finished ready for veneering:

Curved string with croch joints

Curved string with croch joints

Here’ s a short video showing how I edit the Stairdesigner DXF file to get the exact shape of the form and laminates:

(We apologise for the the quality of this rather old video. Nonetheless, we wanted to include it for the advice it contains on fine-tuning the design in AutoCAD.)

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