I've been making hula hoops for about two and a half years. I've tried to include here the wisdom I have gained from making lots of hoops. I use the tools that I've found in my mum's garage, as you may not have the same tools, I've tried to suggest possible alternatives.
Step 1: You Will Need ....
*MDPE water pipe
This blue tubing comes in 25mm and 20mm diameters. You can get it from DIY stores like Wickes or Screwfix. Unfortunately the smallest length it comes in seems to be 25 metres.
25mm tubing is good for adult hoops. I use 20mm tubing to make lighter hoops for more experienced hoopers, for hand hooping and for children.
This is the part I've had most problems with. You want something that fits snugly into the water pipe, so that the join won't come apart. You also want something strong which won't break. For the 25mm piping I have found that a short piece of 20mm piping makes the best connector, but clearly it isn't worth buying 25m of pipe to make a 10cm long connector.
An alternative is to use "pipe inserts" which are little tubes with a ridge round one end. These are designed to strengthen the pipe at joints and therefore fit very well in the pipe. They are usually available from the same places where the piping is sold. I use these for hoops made with 20mm pipe.
You might also come across something else that can be used as a connector. Fancy Tapes sell barbed connectors, but I haven't tried these. For 25mm piping you need a connector with an outside diameter of around 20mm, for 20mm piping you need a connector with a diameter of around 15mm.
To get the connector into the pipe you usually need to heat the pipe. I use a hot air (paintstripping) gun, but hot water, a fan heater or some other source of heat will probably work just as well.
Sometimes a connector will stay in place just from using heat, but not always. I therefore use glue. Most glues won't work with the polyethylene which the piping is made from. The only glue I have found that does work is Loctite Super Glue All Plastics.
*Pipe cutting device
I use a copper pipe cutter to make a groove in the pipe and then slice through with a stanley knife. I used to use a hacksaw, but this leaves a rough surface at the pipe ends which needs to be filed or sanded down. You can also get a special tool to cut plastic pipes.
For cutting the duct tape.
*rag or cloth
For wiping up glue
*secateurs or file
If you are using a pipe insert as a connector, you will need to either cut or file off the ridge round one end of the pipe insert. I have a pair of secateurs which are good for this.
in case things go a bit wrong
*tapes for decoration
to make the hoop grip better, and of course, look pretty.
Step 2: Cutting the Pipe
Most people find that the bigger a hoop is, the easier it is to hula hoop with. It is usually recommended to have a hoop that comes somewhere between your navel and your chest if you hold it up against you with one edge on the ground.
If you know the exact diameter of the hoop you want, you can work out how much pipe you need and measure it off, though you may need help with holding the tape-measure. I usually form the hoop from the end of the coil, and adjust it until I get the size I want, to work out where to cut the pipe.
To cut the pipe I use a pipe cutter (designed to cut copper pipe) to make a groove in the pipe, then cut the pipe with a sharp craft knife. The pipe cutter squashes the hoop near the cut, which might make the tube fit more closely round the connector.
You can also use a hacksaw. If you do, file or sand any rough edges off the edges of the pipe.
It doesn't matter too much if your cut is a bit squint as you'll be covering the join with duct tape.
Step 3: Connecting the Ends - Preparing the Connector
Step 4: Connecting the Hoop - Inserting the Connector
Using a marker pen mark the centre of the connector - you don't have to do this, but it helps later.
The plastic glue has two parts, a primer and the glue. Apply the primer to half of the connector. If you are using a pipe insert its better to start the half with the cut-off rim as this may grip the inside of the tube better. Apply the primer to the inside of one end of the tubing. I sometimes mark this with the marker so that I know which end I have done.
Wait for a minute (according to glue instructions), then apply glue to the primed half of the connector.
If the end of the connector doesn't slide into the end of the pipe, heat the pipe - a few seconds with a heatgun usually does the trick. Don't use to much heat to start with - ideally you should need some force to get the connector into the hoop. Once I have the end of the connector in the pipe I press it the free end of the connector down on a table to get it further in. This is where having a centre-mark on the connector can be helpful.
If you are unlucky, you might push the connector in too far. In this case you might be able to pull it out with pliers. If you have end up with less than 15mm of connector sticking out, then it's better to cut off the part with the connector in off and start again, as otherwise the join is quite likely to come apart. I find 20mm pipe inserts are the worst for this happening - the ones I have been using are quite short.
I usually wait for the glue to dry before repeating the process for the other end of the pipe. This is because I don't want the connector to get pushed further into the first end of the pipe when I'm trying to push the second end on. At this point it is a good idea to make sure that nothing has fallen inside the hoop. It can be quite annoying to have something rattling in your hoop. Unless you want a rattling hoop, in which case, this is the time to put rattling items in the hoop.
You might find that once the second pipe-end is on the connector, is is quite difficult to get it to move along so that the ends join up. To get them to join hold the hoop vertically with the join between your left and right hands, and the bottom of the hoop on the ground, then push the joint up and down. This looks rather strange, and its quite slow and hard work, but I guarantee the ends of the pipe will slowly move towards each other. The other thing you can do is wrap some tape (the more scrunched up the better) around the hoop on either side of the join to give a better grip when you push the ends together.
After waiting for the glue to dry, you can test the join by trying to pull it apart. If I'm feeling brave, I put my foot on one side of the hoop and tug at the other end of the join. If the join doesn't hold, glue it again!
Step 5: Taping the Join
Congratulations! You have now built a hula hoop.
Step 6: Hoop Care
Hopefully you will have a nice round hoop, but sometimes it can be a bit wonky. This can also happen if you leave a hoop beside a radiator or squashed into a cupboard. If the hoop is not flat, place it on a flat surface and put something heavy (books are good) on the parts which lift up for a few hours. If it is not very round, you can try squashing the hoop to reshape it a bit.
If you want you can use tapes, or anything else you can think of to decorate your hoop. Decorating the hoop not only makes it look nice, it also improves the grip and makes it easier to hoop. Whatever you decorate your hoop with needs to be tough. However, if your hoop is looking a bit shabby, you can always put on more tape, or take off the old tape and put on new (WD40 is helpful for getting old stuff off).