As a professional builder of hollow wooden paddle boards I have a lot of clamps. One of the handiest clamps I use are these spring clamps made from 4" Schedule 20 perimeter drain pipe. These clamps were originally made for building the rails on my wood paddle board kits, but this summer my wife started stealing them for holding down row-covers in her garden. The clamps do not have crushing clamping force but for their weight they are surprisingly strong. There are many things that make these clamps really awesome:

They can clamp at weird angles.
They can be used individually with a very light touch or nested together to increase there clamping force.
They stay put on narrow edges where other clamps eject themselves
They are rust-proof
They weigh next to nothing

Probably the coolest thing is they are made from the waste cutoffs that would otherwise end up in the landfill. Every new construction project throws out enough perimeter drainage pipe cutoffs to fill a Rubbermaid with these clamps. It is because of this upcycling benefit that I feel this secrete should not be limited to just wood surfboard builders.

Step 1: Layout Marks

If you are going to make 1.5" clamps you will start by marking your pipe every 1 5/8". 1.5" plus the thickness of your saw blade. If you have already made some clamps you can just slide a completed clamp over the pipe as and use it as a marking tool. (pictured)

Step 2: Pilot Holes

Drill a small pilot hole in the centre of each section. Technically you could skip this step but I usually drill the 5/8" holes with the pipe trapped between my feet so the pilot holes are nice.

Step 3: Drill 5/8" Holes

Enlarge your pilot holes to 5/8". It is best to use a spade bit for this hole. Twist bits drill the pipe so quickly that it tends to grab and torque the bit as you finish the holes. Your wrists will thank-you!

Step 4: Trim the "Bell End"

Drainage pipe has one flared "bell end" allowing it to fit over the next length. If the pipe has a "bell end", it is easiest to cut it off first. You can safely do this by putting something under the pipe and against the fence of your mitre saw as a spacers. This keeps the end of your pipe square.

Step 5: Cut the Clamps to Length..

It is important to slice the pipe into 1.5" lengths before you slice the clamps open. Set-up a stop on the cutoff side of your saw to perfectly space your rings at the desired length. Having them all the exact same length is a nice touch when you nest the clamps later.

Step 6: Open the Clamps

The final step is to slice through the 5/8" hole to open the clamps. I like to use either a Japanese handsaw or a bandsaw for this step. The clamp will want to close on the saw blade as it is cut so be careful if you use a table saw.

Step 7: Safety Tip

A 2x4 fits nicely inside the 4" pipe and keeps your fingers away from the saw blade. This allows you to use the whole length of pipe.

Step 8: Nesting

Schedule 20 clamps are most useful when they are nested together to increase there clamping power. If you are using schedule 40 pipe you probably don't need to nest the clamps. If you are short on clamps in your workshop you will find these clamps very handy. If you have 100's of clamps in your workshop you will see that there are some jobs these clamps out perform the rest. Enjoy!