Helical Staircase on a Sphere

[kevinBEQFC]

I would like to request some help on designing a helical staircase on a sphere.  I'm not a newby, but am certainly new to attempting this design. I can get a guide spherical/helical guide rail. But can't figure out how to extrude the stringers and get them not to twist, as well as making a pattern on path for the stair treads, and not having them twist. Thanks in advance.

[Warmingup1953]

As in this Petrochemical Storage sphere?

[kevinBEQFC]

Yes sir.

[Warmingup1953]

Interesting challenge.....My WIP:

What is your end goal? Size?

[kevinBEQFC]

I'm a professional scale modeler. I'm producing a scale model of a smaller one of these. 5" diameter with 9 legs. I've tried sweep+rail+guide, lofting with a rail, pattern on path with a body, drawn the profile on a plane on path. They all twist. And I'm not sure why. On a helix it's fine, but once I trim the helix onto the sphere, twist every time. I'm sure it's something I'm not doing, or I'm just not aware of. Any help is appreciated.

[Warmingup1953]

My first go is by using Thicken...as a means to avoid twist I'll need to get back to it when time allows but here's my very rough go...

[etfrench]

Here's a really tedious method😁

1. Model the sphere.
2. Create a Surface workspace helix.
3. Split body the helix with the sphere, discarding the inner part of the helix.
4. Offset the sphere, the width of the stairs.
5. Split the helix with the offset, discarding the outer part of the helix.
6. Thicken the helix.
7. Create a rectangular pattern of horizontal lines wider than the helix and the height of each step.
8. Split body the thickened helix with the lines.
9. Create a plane at angle at the top of each step.
10. Split body each step and remove the excess.

[kevinBEQFC]

Good morning,

So, when I attempt to split body, I get an error telling me "The are unhandled intersecting tool data. Try without intersecting tools." I don't understand how you'd split the body without a tool intersecting it. If I use trim, it allows me to cut the helix, but that doesn't leave me with bodies to work with.

Also, when creating the helix, I'm having to do with with two coils, and then creating a sweep between 3D geometry to make the helix. Is this how you are getting your helix? I noticed that there used to be a helix function in 360, but that is gone.

[laughingcreek]

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@kevinBEQFC wrote:... I noticed that there used to be a helix function in 360, but that is gone.

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It's called "coil", under the create menu.

[kevinBEQFC]

So I now have the stringers following your lead. I have a pre-made stair tread. Now the issue is if I perform a pattern on path for the treads, the treads twist as the path progresses. No option for a guide surface here. I'll have to experiment a bit. I'd hate to think I'd have to manually install each tread to get them straight.

[evanp4509U4JZ]

I THINK this worked. Timeline is a mess but it basically is createsphere, create tread surface body, pattern tread surface body on path upwards from sphere centerline, create sphere zero offset surface, create tread width sphere offset surface, create spiral, copy spiral and rotate tread depth (I did 1.5 degrees), split and remove using sphere offset surface, tread width sphere offset surface, spiral, and tread depth rotated spiral surfaces.

I think.

[kevinBEQFC]

The treads aren't symmetrical though. I'm still not wrapping my noodle around why the premade treads I have would twist as they climbed the helical path. I have a feeling the calculations aren't there in the program to deal with the Helical Sphere geometry.

[etfrench]

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@kevinBEQFC wrote:
Good morning,

So, when I attempt to split body, I get an error telling me "The are unhandled intersecting tool data. Try without intersecting tools." I don't understand how you'd split the body without a tool intersecting it. If I use trim, it allows me to cut the helix, but that doesn't leave me with bodies to work with.

Also, when creating the helix, I'm having to do with with two coils, and then creating a sweep between 3D geometry to make the helix. Is this how you are getting your helix? I noticed that there used to be a helix function in 360, but that is gone.

---

The helix is created in the Surface workspace using the Sweep command. It needs to extend past the sphere both horizontally and vertically.

Note: You can create a wide helix using a rectangular coil, then Press/Pull one side.

[user015M86Y]

Hi, here is my proposal :everything is done with emboss and replace face

See timeline procedure and Fusion 360 - Embossed Text on Sphere

https://www.youtube.com/watch?v=G-9GNVpYjk4&t=309s

https://a360.co/3WOzgq3

[jasonlthornton]

I help make stringers like these where I work. If it's on the sphere its going to twist due to the compound bend. Compounds change in pitch throughout the bend which never seems to work well. Even tapered stringers work becuase each half coil is close in developed radius when bouncing between 2 center points equal distance from the main center. I normally break these into sections that appear close enough. The picture hides it but you can see a transition kink between rail section 4 from the top. Treat it like a pitched ellipse.

[davebYYPCU]

Need more info.  Can automate a lot of it, just have to manually place the treads.  5 inch tank.

How many Treads?  My constant / Copied Treads give me variable riser distances.

@evanp4509U4JZ  has constant risers and a big difference in the Treads.  (More likely)

Presumes you want to finish Top Dead Centre, 

How far to Sweep to the Equator I have 180 degrees for the Treads but half diameter.

[MichaelT_123]

Hi Mr KevinBEQFC,

“Helical Staircase on a Sphere” – perhaps this is the unfortunate name simplification.

A helical spiral has cylindrical symmetry/association. Yes, a helix is a spiral,  … but not all a spiral are helixes (oh, I said this before: https://forums.autodesk.com/t5/fusion-design-validate-document/create-a-spiral-line-in-a-3d-sketch/m...)

Assuming we are talking about stairs with equal treads and rises, the curve generated by such structure will have a specific shape. It will be a spiral (in most cases) but not a helix … in a strict sense.

What kind of spiral is it, then; can we encounter it in real life (if such exists?) or perhaps in the virtue of mathematical abstraction? Well, if I find some vigour, I will explain some of its intricacy in the successive separate posts.

Still, to address your specific request, I am attaching the traditional hard-yakka-laboured-semi-parametric Ffile. It is not highly optimized, but I hope it will give you an idea of how to pursue your project.

Attached files:

SpiralOnSphere_A_arcd.png       4K_stereo ( 1.2MB)   https://a360.co/3ABUS05

SpiralOnSphere_mono.png         4K_mono  ( 0.7MB)    https://a360.co/3AD6csQ

SpiralOnSphere.f3d                      F3D            (0.4MB)     https://a360.co/4740nRd

Regards

MichaelT

[MichaelT_123]

FYI ...

https://forums.autodesk.com/t5/fusion-design-validate-document/stairs-on-sphere-nontraditional/td-p/...

Regards

MichaelT