A torus is a circular tube. You might want to make one as part of a toy or ornament, for a school science project, or, as in my case, as part of a prototype to test an invention. Bending metal tubing requires a completely different process to bending PVC (plastic) tubing. There are at least three reasons why you would prefer PVC over metal.
- PVC is lighter
- PVC is cheaper
- PVC does not interfere with magnets
There might be easier methods, but the method i'm going to describe worked the best for me. I am using a tube of 25mm outer diameter with 'walls' 2mm thick. The diameter of the torus in relation to the tube diameter is rather small. That is, i need to bend the tube a lot. This caused problems which i had to solve...
Printed on the tube is "25mm".
To make a torus of diameter D, the tube at the end of the whole process will be D times pi. For instance, i want a torus with average diameter 230mm, so the length of the tube (circumference of the torus) will be 230 times 3.1416 = 723mm. So you need a piece of wood (the "mould") at least as thick as your tube diameter (e.g., d = 25mm) and big enough for you to make a hole in it, where the hole is D + d.
The problem is that if you try to bend the whole length of the tube (e.g., L = 723mm) to form the torus in one go, the ends of the tube will probably deform due to the heat (see later), and if you use a piece of tube even slightly too long, you'll have overlap in the mould and the torus will be deformed. The solution: make two crescents. The length of tubing to make the crescents is L/2 + 100mm. L/2 is half the circumference and 100mm is an extra piece which you'll cut off later to get rid of the deformed ends.
You will need
- thick gloves to prevent you burning your hands,
- electrical/insulation tape to seal the tube ends,
- sea sand or fine salt to heat up and pour into the tubes,
- a funnel (i made one out of two pieces of A4 size paper; make the top opening nice and big and the bottom opening the right size for your tube diam.),
- a pan to put the sand/salt in to put in the oven,
- a spring which can fit snugly inside the tube and which is at least as long as a crescent (L/2 + 100mm) and
- an oven.
- I wore two pairs of gloves, one over the other.
- It takes two people to do this, one to hold the tube and one to pour the sand in.
These are the steps:
- Cut two equal lengths of tubing for the two crescents (L/2 + 100mm, e.g., 723/2 + 100 = 461.5mm).
- Seal one end of each tube with insulation tape. Have some tape ready to close the other ends later on.
- Put the pan containing the sand\salt in the oven.
- Set the oven heat to 230 degrees Celsius / 446 degrees Fahrenheit.
- Let the sand heat up for 30 minutes.
- Put the spring into the first (second) piece of tube.
- Put on your gloves.
- Take out the pan from the oven. Careful; it is VERY hot.
- Spoon some sand into the tube thru the funnel. My 461mm tube took only 3 and a half scoops (the spring takes some space).
- The tube will become limp in about 10 seconds.
- Seal the other end of the tube.
- Guide the now flexible tube into the wooden mould.
- Make sure the tube is pressing neatly against the sides of the wood in the hole.
- Hold the tube in place for 2 or 3 minutes.
- Now leave the tube there. Don't remove it from the mould for approx. 10 minutes, else the spring will want to straighten the tube.
- Place the pan in the oven again.
- Come back after 10 minutes, remove the crescent and repeat from point 6 with the second piece of tube.
- Switch off the oven.
You'll find that the ends of the crescents are deformed due to handling. From each end, cut off half of what was added (i.e., 100mm/2 = 50mm). Now you should have two half circles. Glue them together with "PVC cement" to get your torus!
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