Help with drawing a spiral staircase


I’m trying to draw this curved staircase that’s basically two sheets of bent steel with triangular runs. I drew the runs the way I want them, with the correct elevation, spacing, angle, etc. The main problem is the outer wall and inner wall. I’m trying to make the wall follow the same line as the runs, so it would be at a constant 38" from the nose of the runs. So far, what I manage to draw is basically a half cylinder. But everything I try to resize it, it deforms the cylinder and pushes it away from the runs at the center. Any clue as to how to do this? I would obviously like to do the same with the inner wall (which I haven’t drawn yet).

Thanks in advance,
stairs.skp (74.3 KB)

This is for desktop version with plugins

Which version of SketchUp are you actually using? Your profile is confusing. I have some suggestions but they depend on the version and what tools you have available.

You really should keep your model close to the origin and in this case, centered on it will help. You have it about 1000’ away from the origin.

Here’s an idea that uses only native tools and will work with any version of SketchUp:

  • draw a vertical edge from the floor-level inner corner of the bottom tread up to the height of the wall
  • draw another vertical edge from the inner corner of the top tread down to the floor level and then extend it up to the wall height
  • draw an arc between the floor-level ends of the two edges and with radius equal to the inside radius of the stairs
  • move a copy of the arc up to the top of the edges
  • stitch the vertical edges between endpoints of the top and bottom arcs to fill in the wall
  • soften/smooth the interior edges to make the wall look smooth

Edit: here’s an animation of the process. I added another helper edge down from the middle step to make it easier to get the arc radius. Ooh! It appears the forum software shrank it down tiny. You may have to zoom in your browser to see it!

Edit #2 Redid it with a smaller file. You should be able to see this one.


I hit that snag, and it got discussed here.

There’s almost always more than one way to do it in SU. As an alternative to Steve’s method…

  1. Find the centre of the lower half circle (select the arc, R-click Find Centre)

  2. Draw a circle centred on that, with the same radius as the inside of the steps. Fix the radius along the Red axis by tapping R arrow key, then inference the radius off a step.

  3. Draw a diameter aligned with the end of the steps, and delete the nearer half circle.

  4. PushPull the half circle to height

    5 Delete the flat face and its top and bottom edges

  5. Reverse faces.

Optional - make the inner wall face a separate component, and/or cut to clipboard, change context to the model as a whole, and paste in place (R-click on the selected inner wall face and edges) in the model outside the stairway.

It would have been slightly easier to draw if the diameter of the half circles, and the steps, ran along the red axis.

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Thanks for your help. It seems Mihai.s post does exactly what I want. I have Sketchup Pro 2018, without any plugins or anything.


Thanks for your post. That is exactly what I want to do. You use a plug in called “helix”, is that it?


thanks for you help. The part you drew, that I can do. It’s the helix part that mihai.s drew that I can’t do.

A little easy with Shape Bender

Helix along curve:

Or you can manually ‘stitch’ the helix using the line tool, joining the ends of the steps first, to make the helical shape.

What to you want to do after that? Make the curved steel stringers?

@mihai.s is using a couple of plugins, which you can’t use in SU Free.

So you have to do it the hard way, manually. First make one step’s worth of stringer, then copy rotate it up one step and around one step, then repeat that move as many times as there are steps.

Will try to model it a bit later today.

PS. If you are using SU Free, and not for commercial purposes, you could instead download SU Make 2017 for desktop use on either Windows, or for Mac (which your profile says you use) . That CAN use plugins, and doesn’t depend so much on having an internet connection.

You need one to complete the licensing process but not afterwards, except to download other pre-made objects from the 3D Warehouse, or plugins, most commonly from either or both of the Extension Warehouse, or the SketchUcation plugin store.

For SketchUp Free (web) without plugins


@mihai.s - Classic method of drawing a helix with native tools.

Thank you.

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Amazing. Thanks

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