Shaping a large circular frame out of wood

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Old 11-05-12, 02:31 PM
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Question Shaping a large circular frame out of wood

Hello, I'm new to these forums and apologize in advance if I'm posting in the wrong section.

I'm trying to build a circular dolly track, about 14 feet in diameter, out of 2 inch pvc pipe. I'm planning to use this track to achieve a certain look when filming footage by attaching a tripod with a camera to the dolly.*

The plan is to get a thin pvc pipe and use hot sand to make it malleable, bending it into shape and then letting it cool. My issue is how to do this precisely so that it is as close to a perfect circle as possible?

One idea I had is to make large circular frames out of wood which would serve as a model for the shape of the track (imagine a huge wooden spool cut in half). I could then run the pvc pipe around the frame while it's still hot and get a circular pvc track in the shape of the frame.

Is there any method for making this type of a frame, or can anybody recommend a place that might do this (would a regular lumber yard take on a project like this?). Also, if anybody has any better ideas I would appreciate the input, I'm trying to figure out the best way to go about this.

Thanks in advance.
 
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Old 11-05-12, 04:39 PM
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Hi Mike, welcome!

Well, there's probably a variety of ways to do it, especially if cost is not a limiting factor. The least expensive and most precise way would probably be to get 2 sheets of 3/4" plywood ripped down into pieces that are 12" x 48". Then from those pieces, cut yourself 16 pc that are about 3' long. Each piece will have a 11.25 degree miter on each end so that the left and right ends of each piece look like this: \________/ You would need a 12" sliding miter saw to do this accurately, but a skilsaw would also work if you had a long bevel gauge and an accurate person using the saw.

Assemble those 16 pc with pairs of pocket screws to form a 16 sided polygon, whose diameter will be about 15' across, and circumference about 47.1'. Then get yourself a couple 16' long 2x4's and cut a half lap joint in the middle of each one and lay the half laps together to form a + and position them so that you can brace this entire thing like this: (+) Then screw that together so it can't move, measuring carefully to position the center of the + in the exact center of your 16 sided polygon, and mark an X on the center of the polygon. You might also want to brace the + and the polygon with some additional 2x4's that have been cut with 45 angles on each end. They would need to be about 10 or 11' long to go from point to point on your +.

Now take a 2x4 that's cut 7' 1 3/4" long, and drill a 5/32" hole through one end that is centered on the 2x4 exactly 1 3/4" from the end. Place a 3" screw through that hole and screw it to the X that is the center of the polygon. Now as you spin that 2x4 around the polygon, you can use a magic marker to trace a circular outline that has a radius of 7' or a 14' diameter circle.

Remove the 2x4 that was used for the tracing. You could now attach small blocks of 2x2 around the outside perimeter of this circle, glue and screw them to the plywood, and then use them to clamp your pvc pipe to, helping to bend and hold it into the right shape. Or you could also glue and screw some blocks around the inside perimeter of your pvc which would trap the pvc in place. You might need to install a few blocks across the top here and there as you lay the pipe in place in order to keep it down between the blocks since it might want to flip upward and come out from between the pairs of blocks.
 

Last edited by XSleeper; 11-05-12 at 04:55 PM.
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Old 11-05-12, 05:59 PM
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Do you need a track? Making a track seems like a lot of work and requires a fair bit of precision. Somewhat difficult to DIY cheap and get a smooth camera motion.

Would a wagon, skateboard or other wheeled thing attached to a center point by a rope or chain do the same thing?

You could mount your camera on a long arm with a pivot point in the center and a counter weight so it's roughly balanced.

You can use model railroad track. I have a G scale train that I run around the tree each year and it's rails are 1 3/4" apart. It's large enough to carry a prosumer video or DSLR camera and pre-curved track sections are available in many different radii. There are also larger gauges if you want something to carry more weight without having to worry about balance so much..
 
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Old 11-05-12, 07:56 PM
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Xsleeper, you are on the right track but that is more complicated than it needs to be. Forget making all those pieces and pocket screwing them together. Take your sheet of plywood and cut as many arcs out of it that you can. I'd say have the arc 10" wide would be sufficient. You can nest them together for the best yield. I don't know how long this jig needs to be. Perhaps 8 foot lengths usable. If the jig only needs to be about 3 inches tall, then just secure 4 layers of 3/4" plywood together.
 
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