Revolving Spiral Stairs

[Ech725]

Alright, I get to tackle my first spiral staircase. This particular staircase will revolve. Initially, I was thinking it would be a spiral staircase on top of a revolve but the designer went a different direction. Since I was given drawings early (Always a plus), I decided to draw it up in sketchup (I've attached some pics).

Things I have to consider:

The unit will be loaded in a 24' truck. (Right now the diameter is 8' 10" but it may be decreased)

The unit may have to be loaded out and back due to scheduling of the theatre.(So I'm thinking modular building)

The budget will not allow a pre-fabricated unit

I was not sure if the shop had welding capabilities (summer gig-but found out there is a mig welder and chop saw) so I started focusing on wood. I looked at multiple prefab images and also checked out the technical design solutions for theatre vol. II article. So I have in the model a 3.5" sch 40 pipe as the column. The spacers are 4" pipe. The treads are two pieces of 3/4" ply laminated. The riser is 3/4" ply attached to tread with a dado. The steps are faced with 3/4" ply. The pivot point is 3" pipe on a flange. The supports are 4x4 that will attach to the unit with 6" castors. The bottoms will be decorated with a newel post.

Questions:
Has anyone built a spiral with the spacers and wood treads? Did it work well?

Any recommendations for attaching the supports to the stairs? To the railing?(I was concerned about having enough material to attach to so the facing was beefed up to 3/4"-some blocks could help on the inside but they would have to covered.)

I haven't figured out the weight of the unit but was considering adding two more supports. Thoughts?

Any thoughts on attaching a removable railing?

Any other suggestions or tips?

 

[Footer]

Your not going to like my answer, but this is not going to work. No way doubled up 3/4" ply around the center colum is going to be able to take the load of a person on the edge of the stair. Added to that those extra legs are just going to rip off under the load without some bracing. You might be able to do that with steel, but even this that is a big might.

I would start with a kit spiral staircase and go from there if you can't weld.

 

[Ech725]

I was thinking that the diameter of the stairs was a bit large at over 8'. That's why I was ruling out prefab because the large the dia the more it cost. I'm hoping the dia can be decreased. In the tech solutions article, they used large washers in between the spacers on top and below each tread. I imagine that would stiffen things. Or maybe tripling the plywood to 2.25".

This build used PVC.

 

[Footer]

I was thinking that the diameter of the stairs was a bit large at over 8'. That's why I was ruling out prefab because the large the dia the more it cost. I'm hoping the dia can be decreased. In the tech solutions article, they used large washers in between the spacers on top and below each tread. I imagine that would stiffen things. Or maybe tripling the plywood to 2.25".

This build used PVC.

View attachment 9460

View attachment 9461

The issue you will run into is the ring that holds the thing around the center pipe. There are a ton of forces at work (especially at 4' out). Plywood is very strong, but when you cut holes in it then try to hold it up with the hole, you can run into some real tearing issues. PVC and steel don't have this problem.

This project sounds fun to do, but plywood is not going to be your friend. Look at kits or the used market. Otherwise, might be worth buying a steel chop saw and getting a metal shop going.

 

[Van]

Metal is about the only way this is gong to work. I had one of those plywood spiral staircases in my shop when I first took my present job. I threw it away rather quickly. Even when well made they are creaky and you certainly don't build them out of anything less than a good "super ply".
I'm going to attach a dwg of a staircase I did for our production of Streetcar a few years ago. you are more than welcome to use it if it helps and if you get access to a metal shop and welder.
streetcarspiral

 

[Ech725]

Metal is about the only way this is gong to work. I had one of those plywood spiral staircases in my shop when I first took my present job. I threw it away rather quickly. Even when well made they are creaky and you certainly don't build them out of anything less than a good "super ply".
I'm going to attach a dwg of a staircase I did for our production of Streetcar a few years ago. you are more than welcome to use it if it helps and if you get access to a metal shop and welder.
streetcarspiral

I get confirmation this weekend about the welder. I have checked out the drawing. Thank you.
So you notched, bent back and rewelded. I imagine some sort of jig helped. And you welded the frame to the 4" spacer pipe and stacked them over the center column.

When you attached the frame to the pipe spacer did you just cut an angle and filled in the gaps or did you cut a curve?

Did the balusters and railing lock the treads from spinning?

Did you use steel for the railing?

I'm curious-how much of the budget did the staircase eat up?

I appreciate the info.

 

[BillConnerFASTC]

I'll take the contrarian view and say I'm not so sure you can't build this out of wood. Look at some articles in Fine Homebuilding. I think that the wedge would have to be more like box with front (riser) and back opposite, and a bottom, and then the just solve the tension on the "ring" you are showing around the center pole. It's a shelf bracket, and just some metal on the top - or between the two layers - might be all that's needed. taller risers would of course help but you need close to that to get head clearance. 8' diameter is probably beyond this but maybe 6' or 6'6. Let treads overlap so the baluster passes through one and sockets in the one below - probably pipe and sleeves with pins or set screws.

Still probably easier in metal. I read and saw pictures of one made with concrete - just case the treads with a pipe sleeve and rebar one at a time and stacked them on the center pipe. You need to make that plywood box as strong - but not as heavy - as the concrete. Could simplify the construction with a pipe sleeve and a couple of plates welded on to provide a good attachment for the plywood treads and bracket.

You have to show pictures of whatever you do with this.

 

[Van]

I get confirmation this weekend about the welder. I have checked out the drawing. Thank you.
So you notched, bent back and rewelded. I imagine some sort of jig helped. And you welded the frame to the 4" spacer pipe and stacked them over the center column.

When you attached the frame to the pipe spacer did you just cut an angle and filled in the gaps or did you cut a curve?

Did the balusters and railing lock the treads from spinning?

Did you use steel for the railing?

I'm curious-how much of the budget did the staircase eat up?

I appreciate the info.

We attempt to use a end mill and cut an arc out of the end of the 1x3 to make the mating nicer. Our tooling,unfortunately, didn't hold up very well. So we simply cut the ends at an angle so that when mated to each other then welded to the spacer ring there wasn't much of a gap to fill at all. Yes building a fixture to hold the center pipe square and plumb while also centering and squaring the tread pieces to the pipe section was key to the success of this project.
Something not shown on those drawings is that after notching, bending and welding the 1x3 tube, I added a piece of steel, overlapping the joint as reinforcement.

The Spindles were set on the outside edge of the treads, laid out so that one attached flush with the back edge of one tread and attached to the next one up on it's front edge. This served to lock everything in place.
I was going to use steel for the hand rail but ran into a scheduling issue with my bender. We wound up building the railing by laminating layers of 1/8" masonite one at a time in place on the staircase. We routed the whole thing and wrapped it on Gaff then painted it. I looked fantastic but it took longer than I wanted. Basically just getting a length of 1x1 having it bent into a gigantic circle, the diameter of you staircase, then pulling on it like a slinky would have been so much faster, and perhaps a bit easier. I

It wasn't all that expensive over all the largest cost was in labor. I think that set had a really small budget, like $2500. or so. The staircase was a drop in the bucket.
I had to brace the top of the center support to a 16' long cantilever-ed custom Triscuit that I built to span 14' unsupported. Then only issue I have with your revolving unit is that I would build the revolve that it sits on as at least 4'-6' wide. The Stresses on the connection point of the central shaft are going to be significant. Imagine a 150 pound actor standing in the middle of one tread: you've just added something like 300 pounds of lateral load on that point, not multiply that by however many feet up in the air that tread is. Your Idea of putting legs on the unit is well meaning but the lateral forces on a leg trying roll a caster is going to cause it to fail at the worst or to jump, stutter and snap it's way around it's pathway.

 

[BillConnerFASTC]

You do need to know how this will be used. A typical spiral that is only permitted to serve a very few occupants for egress - like a gridiron or catwalk - is a lot different than one with a member of the chorus on every tread moving to the music.

 

[Van]

Very true Bill ! Very true.

 

[BillConnerFASTC]

Very true Bill ! Very true.

I'm not sure of the ones I've seen complete that they would hold up to an energetic production number. Then I was backstage when a storage mezzanine - a properly designed one - when "crack" when a director decided to use it for a chorus - 12 actors chanting and jumping in unison - and they all very quietly tip toed down the stairs. Kind of illustrated why a storage area is OK at 50 psf and a stage is typically designed for 125 or 150 psf.

 

[Ech725]

Then only issue I have with your revolving unit is that I would build the revolve that it sits on as at least 4'-6' wide. The Stresses on the connection point of the central shaft are going to be significant. Imagine a 150 pound actor standing in the middle of one tread: you've just added something like 300 pounds of lateral load on that point, not multiply that by however many feet up in the air that tread is. Your Idea of putting legs on the unit is well meaning but the lateral forces on a leg trying roll a caster is going to cause it to fail at the worst or to jump, stutter and snap it's way around it's pathway.

I got confirmation that I WILL be able to weld so that's a plus.

Well, I originally was thinking the staircase would be on on top of a revolve, but I do not think the designer wanted that look.

How about anchoring the pivot point to a 4' to 6' piece of superply?

 

[DuckJordan]

Why not make a steel foot structure that's raised 6 inches similar to a platform?