You may need to cut a pipe in half lengthwise for a number of reasons. A viable way to cut round PVC or non-ferrous metal pipe lengthwise is with a band saw. An accurate, straight cut on a band saw is best made by creating a box-like jig to contain and hold the pipe steady while running it through the band saw. Make sure that your band saw has a blade designed for cutting plastics or metal.
Things You'll Need
Nails or screws
Use a tape measure to measure the diameter of the pipe.
Create a box to hold the pipe while cutting it. Create the box out of 3/4-inch thick strips of plywood. Make the interior width of the box the same size as the pipe diameter. Make the depth of the box half the size of the pipe diameter. Make the length of the box equal to the length of the pipe you're cutting. The box only needs three sides: a bottom and two long sides. Leave the short ends and the top open. Use wood glue and nails or screws to assemble the box.
Set the pipe in the box. Exactly half of the pipe circumference should stick out above the sides of the box.
Affix the pipe to the bottom of the box either by screwing it or by using small clamps.
Add together the length of the box depth (half the size of the pipe diameter) together with the thickness of the wood you're using (3/4-inch). Set the band saw fence this distance from the band saw blade.
Set the box with the pipe in it on its side so the bottom of the box is vertical and is resting against the band saw fence.
Turn on the band saw and slowly push the pipe through, keeping the bottom flat against the fence. The blade should run just along the lips of the box, thereby cutting your pipe in half.
Always wear your safety glasses when cutting materials on a band saw.