There are different ways to make your own centering rings. The best method will often be determined by the materials you are working with. The technique shown here is intended for plywood (or similar) rings, 1/8" to 3/4" thick. For materials such as cardstock, for low power rockets, you can use a compass and a hobby knife to make centering rings. Circle cutters are available which are like a compass with sharp blades attached to them. For plywood, you can use either a circle cutter or hole saws. Each has their own advantages.

The main advantage hole saws have to offer is no setup required. You know exactly what size hole you'll end up with by picking the correct hole saw. While hole saws are available in many different sizes, you may not find one perfect for your project. A Little sanding can take care of that quickly.

I decided to go with a circle cutter to avoid sanding and to lower the labor involved. With a hole saw, you need to make two cuts (inner and outer diameter). With a circle cutter, only one cut is needed.

Circle cutters (aka hole cutters) come in various sizes and models. They all do the same thing. The one on top allows for much larger circles to be cut. Before making a cut, check the blades and made sure they are facing the right way to get clean cuts. You can also use these to cut bulkheads, simply remove one of the blades. This is the case for the one shown on the bottom right.

For accuracy, a drill press is used. While you could attempt this with a regular drill, I know I just can't keep a hand-held drill that steady.

OK, by now you're probably thinking... a drill press is expensive and I wanted to make cheap rings... There's a difference between making your own and going cheap. There are plenty of benefits to making your own, other than price. You can cut rings for odd-sized tubes. You make your ring when you need it. Your project won't be delayed while you wait for centering rings to arrive.

Here, a centering ring is about to be me from a scrap piece of plywood. It is a fin that wasn't cut correctly and will be recycled as a centering ring. When using a drill press, clamping down the part you're about to drill/cut is crucial. Not doing so is downright dangerous. Position the table so that the plywood is in the correct location. To check this, lower the circle cutter close to the wood and check that the outer ring will fit inside the wood piece. Lock the table in place and drill away.

Take your time making these. Drill slowly and at a slow speed. Trying to hurry things will result in burn marks and blades going dull very quickly.

When you drill a ring in one go, the bottom side of the ring can have some chipped strands of plywood. While this won't affect performance, it doesn't look quite perfect. For a better looking ring, but the ring halfway. Then, turn over the wood piece, clamp it into place and finish the cut.