15 Replies Latest reply on Feb 20, 2013 9:13 AM by Suraj Sethi

    Circular stairs

    Demitri Duwadi

      Hello all,

       

      I'm constructing a large LNG tank and I need help on making a helix staircase that goes up it with the guard rail and possibly the small set up at the top if I can make it, similar to the attached picture. I'm unsure about how to start it though as I've never done helical extrusions, It's possible to do a small rectangular extrusion every x amount of distance over and x distance up, right?

       

       

      Also on a unrelated side note, is there any simplistic way that allows two people to work on one project at the same time like google documents? Because I feel that would be amazing.

       

      Thanks.

        • Re: Circular stairs
          Timothy Holman

          You could create a single step and then do a curve driven pattern.

          • Re: Circular stairs
            Adam Snow

            An updated file is attached, but it is saved in SW 2013, so hopefully the Backwards Compatibility is working.

            A curve driven pattern for the stair and vertical railing works well. The hand rail was completed with a separate sweep.

             

            A screenshot is also attached that shows the feature tree.

            Due to the scale of this model, the helix did not seem willing to continue to the top.

             

            Spiral Stairs.jpg

              • Re: Circular stairs
                Demitri Duwadi

                Thanks so much for the help! The backwards compatability isn't working, sadly. I would have loved to have seen the file and try to re-create a version of my own. Having something to work off of is always really helpful.

                 

                What plane did you start the rectangle on for the stairs?

                • Re: Circular stairs
                  Demitri Duwadi

                  I see you have a helix, did you have to create that to get the stairs to follow it and gradually go up? Because I can only get my curve pattern on the starting plane to go forward, backwards, left, and right but not up and down.

                    • Re: Circular stairs
                      Jeremy Feist

                      here is a 2012 model with the curve driven pattern. I did not spend the time to work out the stair pitch etc. to make it right, or add the top railing. but hopefully this will get you going.

                        • Re: Circular stairs
                          Demitri Duwadi

                          Thanks, I really appreciate you going out of your way to help! I've been messing with it and I almost figured it out I think, this will be quite helpful.

                          • Re: Circular stairs
                            Adam Snow

                            Jeremy,

                             

                            Good model! Thanks for uploading a SW2012 version.

                             

                            Did you notice the way the stairs have a slight overhang on their outboard faces? I had the same result.

                            I planned to use an offset surface to trim off the stairs and have a nice smooth face remain.

                             

                            It must result from the horizontal/vertical stairs trying to follow the helix. The overlap is only about .023" in your model.

                              • Re: Circular stairs
                                Jeremy Feist

                                yes, I noticed it. if you look under the stairs there will be an overhang there as well - at the tank wall.

                                 

                                a circular trim or offset surface will work for the outside (before or after the pattern) - or the stair tread could be modeled more like a pie wedge to start with. depends on the level of detail needed for these stairs.

                            • Re: Circular stairs
                              Adam Snow

                              On the bottom of the model, draw a circle (or convert the edge to a sketch entity).

                               

                              Now use the curve command to turn your circle into a helix. I used a height of 720 and a pitch of 7874 (reverse direction, 90° start angle, Clockwise)

                               

                              For my stair sketch plane I selected the starting point of the helix (on the bottom of the model) and created an offset copy of the Right plane at the start of the helix. So just select the start of the helix, and the right reference plane, then Insert – Reference – Plane.

                               

                              The stair step was a simple vertical line and a horizontal line to represent a riser and a tread. I made both about 12” long, but later reduced the riser to about 8” to better match the rise induced by the helix. I extruded the stair sketch as a thin feature with a thickness of 3” and a midplane extrusion of 73”. This allows the stair to “embed” themselves within the model and can help avoid errors later.

                               

                              The railing support was added next. Just a circle sketched onto the top face of the stair tread and extruded about 48”.

                               

                              Next up is the curve driven pattern. For this the helix was selected as the direction. I used 150 stairs (instances) with a spacing of 12.5”. Transform Curve, Tangent to curve options. This feature is a bit calculation intensive and I think it would have solved faster if I kept the stair and railing as a separate body in the model and done a body pattern instead of a feature pattern.

                               

                              Now for the railing:

                              First a sketch plane is needed, so I selected the top of the first vertical railing support and created an offset plane 2” downwards. On that plane I sketched a circle and made its diameter so that its circumference fell right on the center of the vertical railing support.

                               

                              Now use the Curve commands to turn the circle into another helix. The height and pitch should match that of the first helix.

                               

                              Now select the start point of this new helix and the helix itself and insert a new reference plane. This time it will be Normal to Curve.

                               

                              On this new reference plane, sketch a circle that is centered on the helix (coincident or pierce). I used a 2” diameter. And now create a new swept boss that uses the 2” circle as the profile and the new helix as the path.

                          • Re: Circular stairs
                            Suraj Sethi

                            Hey Demitri,

                             

                            Here's a video tutorial that you might find handy:

                             

                            http://www.youtube.com/watch?feature=player_embedded&v=2HPVCLCd46k

                             

                            Suraj