A platform, any shape.Wheels.A pivot point.A method of keeping it from wandering off the pivot point.A drive. This can be hand driven or motorized.A method to stop it from turning. A brake and/or locking device.
Let’s start with a basic, round turntable. The pivot point is in the center and the round platform doesn’t need to move anywhere else on stage. On paper, we start with a drawing of a circle. We add the required framing for the platform. We need to figure out the locations for all the wheels. We would use straight casters for this. The shaft of the caster must be aligned with the pivot point. This is very important! Each caster will be traveling on a continuous curved line that doesn’t change. If you were to use swivel casters, it would be harder to get the turntable to turn in the reverse direction.
When you want to have a platform revolve around a single point, using a center pivot point is the way to go. This is easy to do. you can use flanges from you theater supply house. Or, you can also use a flange from your local plumbing supply house. The one seen here is called a Key Clamp flange. Why is this a better choice? The pipe is locked into place via a set screw. This flange does NOT need threaded pipe. The plumber’s flanges does need threaded pipe. The pipe is locked into the bottom flange via the set screw. The set screw of the top flange, mounted on the bottom of the platform, is left loose. This allows the unit to turn freely.
We used black tie line to turn this small unit. for larger turn tables, a metal cable would be used.
How do we figure out the angles for making this circle of wood? Think about geometry. A circle has 360degrees. Let’s say that our wood circle has 20 sections. 20 little tri-angles. 360 divided by 20 = 18. So, the bottom of each triangle has 18 degrees between the two bottom corners. We now need to divide 18 by 2, one for each side, and we get 9 degrees. (Actually, we will get 90 degrees minus the 9 degrees. Therefore, we must make a 9 degree cut at each end of our piece of wood.)
Do you want to double check our figures? 20 seams, 2 sides each seam. That’s 40 sides. 40 x 9 = 360. In the photo, you may have caught that the sections are a little off. Well, we goofed. We cut the sections a bit too long. Since we had just two hours to make this platform turn, we had to be creative right there on stage.