Revolving stage

[Mack]

So... I have a design before me for a 17' diameter (round) by 17' tall set that is basically a giant spiral staircase/castle turret, that needs to rotate in place. It will all be made out of wood. You can see by the size, it's gonna be heavy, especially with actors on it. It will be spun by hand by performers instead of by motor, which I am glad for. The designer did a pretty decent job drafting out the decking, but consulted someone she used to work with about the center pivot point and so is telling me I need a "thrust bearing" for the center. This set will be built in a dedicated space and will only be used for six performances after rehearsals. I can't see why a greased-up pipe sleeve won't work as well, but I haven't built a revolve before so I dunno. Any thoughts? Plus, all the "thrust bearings" I've researched online are like 6-12" wide, and don't really seem like the right part for this kind of job. I'd love some tales of experience. Thanks.

 

[Van]

If your center point is carrying any kind of load then yes you should go with a type of bearing. if the feild is supporting 99% of the load and the center point is merely holding on center, Greasy pipe.
that's my $.02

***nice Sketchup BTW.***

 

[DuckJordan]

The reason you shouldn't used a pipe sleeve is it doesn't offer any kind of mechanism to hold it in place. If its a threaded device what happens when it gets to the end of the threads (it either stops or falls off causing your performers and revolve to fall and injure a lot of people.)

putting a point in the center is going to only be one step in this process... you will likely need casters on the edges to help take the un-balanced load.

Without thinking of budget or anything I would use the thrust bearings, in conjunction with casters on the edges for 17' i'd put "smart" casters (the ones that are able to turn) on 3' centers around the perimeter. so that most of your load is placed on the casters and not the pivot point.

just a heads up your stage will need to be spotless and fairly level or this is going to turn into a very heavy and unmovable circular stair.

 

[Van]

Ok, that's the fourth time today that CB has locked up when I try to run Spell check from my google tool bar. So if you find spelling errors it's because I'm too busy using my brain for important things to care about spelling right now. That being said.....

Duck, If you'll do a search for Turntable or Revolve you find several posts which describe, in detail, why you never use "smart' casters when constructing a turntable. In the same articles you'll find that the best and, IMHO, the only way to construct a turntable is by installing the casters on the floor and having the deck ride on them.
You don't use a peice of pipe with a flange on each end. You use a piece of 2" sch40 and a piece of 1.5" scd40. You ream the inside of the 2" to remove the weld seam, and grind/sand/blast the outside of the 1.5" after aplying a liberal amount of grease and a grease zirt to the 2" pipe you attach it via a pipe flange to the deck. you then attach the smaller pipe to the underside of the turntable. This captures the turntable deck and keeps it from wandering.

 

[DuckJordan]

Sorry, I was just going off of what we used and worked for us. I'll have to check out those other threads. (as you can tell carpentry is not my forte.

 

[MPowers]

I've been in this business for over 50 years and have designed, engineered and built a lot of turntables, from 6' diameter revolving fireplaces to 40' diameter, steel framed, permanent units. You DO NOT need, nor even want a thrust bearing for your unit. I think your designer has mis heard the advice she received from her consultant. A thrust bearing is designed to handle an axial load, parallel to the axis of rotation McMaster-Carr . A turntable puts a radial load, perpendicular to the rotation axis, on the pivot pin. For the unit you pictured, especially if it is to be moved by man power, a common sleeve bearing or a pipe and sleeve would work just fine. If you want a more precise and sophisticated bearing, you want a flange bearing McMaster-Carr click on the mounted bearings. If you Go for the flange type bearing you will need a cold rolled steel axle rod for the pivot pin and it will need to be welded to a plate with 4 or more gussets to support it.

For the unit you pictured, 4" diameter casters are the minimum size you should use, 6" would be better. The best, quietest and smoothest method of castering a turntable is to mount the casters, rigid, (NEVER use swivel casters on a turntable) wheels up (inverted) to a 3/4" ply plate. The inverted position runs smoother and quieter, dirt and debris can't get under the wheels and if desired, electric circuits can be run between the casters to the center where there a number of ways to run the circuit to the turntable. The plywood caster plate sits directly on the floor and needs no framing, just cleats or mending plates across any joints between sheet of ply to prevent them from shifting. The pivot pin (or pivot bearing, either one) is also attached to the ply plate the entire unit can sit directly on the floor and is self contained, so it need not be bolted or fastened to the stage floor. Of course the underside of your deck must have a 3/4" minimum layer of ply along the caster paths to support the rolling weight. Adding a layer of 1/4" masonite to the plywood will provide a very smooth, quiet running surface.

How many casters and the placement depends on what materials you use to build the turntable. There is no specific number or spacing, but a common spacing is in concentric rings. The first ring is about 4' in diameter and each ring is spaced about 4' further away. The casters in each ring are about 4' apart. The reason for the 4' spacing is that the most common materials for framing are 2x4 boards and 3/4" plywood. The spacing is based on the strength of those materials.

Hope this helps, if you have questions, contact me.

 

[Van]

Sorry, I was just going off of what we used and worked for us. I'll have to check out those other threads. (as you can tell carpentry is not my forte.

No Prob, I just wanted to make sure that bit got out there.
The big issue for swivel casters is the fact that if you were to put a mark where the caster hit the floor and then you rotated that caster you'd notice the mark would circumscribe a circle. the point of contact has to orbit for the caster to change direction. The amount of force required to change the direction of the caster can become insurmountable once you put a load on the deck. Just overcoming the initial torsional resistance inheirent in a turntable can be a trick but when you add the amount of extra force require to swivel that caster.... Forget it. Having the casters 'upside down' also means you don't have to worry when a sequin falls of a costume and therough the crack in the turntable. it won't become a wedge under a wheel.

 

[SingForAmerica]

No Prob, I just wanted to make sure that bit got out there.
The big issue for swivel casters is the fact that if you were to put a mark where the caster hit the floor and then you rotated that caster you'd notice the mark would circumscribe a circle. the point of contact has to orbit for the caster to change direction. The amount of force required to change the direction of the caster can become insurmountable once you put a load on the deck. Just overcoming the initial torsional resistance inheirent in a turntable can be a trick but when you add the amount of extra force require to swivel that caster.... Forget it. Having the casters 'upside down' also means you don't have to worry when a sequin falls of a costume and therough the crack in the turntable. it won't become a wedge under a wheel.

Could you help me out on where to find some instructions to a 32' wooden turntable, manually spun, able to handle 30 intense dancers but no set. (I can cut back to around 24' -or whatever works with the math) I downloaded your plans from yearsa ago could they handle the load once i increased the dimensions?

 

[kicknargel]

My instinct (as opposed to structural analysis) would be to double the thickness of the top with two @ 3/4" plywood laminated together. Or frame it, with races supported by the framing. Don't skimp on the quality of the casters. i.e. no Home Depot!