Put together two hemispherical halves of a tube and what do you get? A circular tube, right? Not if the tool that cut them apart removed too much material.

This is what the made-to-print division of Atlantic Fasteners, W. Springfield, Mass., found when a customer asked them to split a 12-in.-diameter pipe lengthwise. Instead of a straight cut, the customer wanted to incorporate two S-shaped splits that would help align the part.

The pipe is a hydraulic cylinder support bearing for industrial injection-molding machines the company maintains. The canvas-phenolic composite that forms the ¾-in.-thick pipe is similar to glass-filled nylon and other reinforced plastics.

The customer had previously tried CNC machining, but even a 3/16 -in.-diameter end mill removed too much material. The reassembled pipe’s cross section ended up elliptical, and many of the parts had to be scrapped.

Atlantic Fasteners tried water-jet cutting with CNC X-Y-Z programming instead. A stream of water with adjustable flow rate, water pressure, and diameter cuts into parts. Plain water cuts softer materials like reinforced plastics and composites. Abrasive media speed cutting or assist in cutting harder materials.

Water-jet cutting can maintain kerfs as narrow as 0.05 in., independent of material thickness. It also does not put thermal or mechanical stresses on the part as traditional machining can.

Atlantic’s engineers found it wasn’t possible to cut both S-splits at once. So, they created a fixture to hold the cylinder steady. The water jet creates turbulence in the water around the submerged part, so the fixture must hold parts as firmly as it would for high-speed machining. A steel block inside the tube stops the jet from cutting through to the other side of the cylinder.

Plain water cut the part cleanly; the addition of abrasive media was not needed. Atlantic was able to create 0.05-in. kerfs that kept the cylinders nearly round and with a smoother finish than endmill cutting. Next, Atlantic machined the ID to true and thinned the walls to ½ in.

The minimal machining required to return the split tube to true round meant the process starts with thinner-walled pipe. The customer saved 30% by purchasing lighter tubes, and Atlantic was able to further cut machining time.