Pipe Cutting, Threading, Bending and Jointing Practical Skills
Cutting
Measure twice, mark clearly, always cut square and deburr. GI/MS: hacksaw with an 18 TPI blade in a rigid frame, light pressure, full strokes. Copper: wheel cutter, then ream the bore. Plastic: fine-tooth saw or plastic cutter, then chamfer the outer edge.
Threading (GI)
Clamp in the pipe vice and chamfer the end. Fit the correct die pair (25 mm = 1 in BSP, 11 TPI), oil generously, start the die square with hand pressure, then cut with the ratchet, backing off half a turn every few turns to break chips. Cut enough thread that two or three threads remain visible when the fitting is hand-tight.
Jointing
- Threaded: PTFE tape clockwise 3–4 turns or jointing compound on the male thread; hand-tighten, then 1–2 turns with the wrench; wipe off excess.
- Solvent weld: clean, apply primer, cement both surfaces, push fully and quarter-turn, hold 30 seconds, cure before testing.
- Copper capillary: clean to bright metal, thin flux, assemble, heat evenly until solder is drawn into the joint, do not disturb while setting, wipe residue.
Bending
Small-bore copper bends with a spring or lever bender; GI is hot-bent with dry sand filling, or cold-bent on a machine. Keep the radius at least 4 × diameter and check for flattening - ovality beyond about 10% means the bend is scrap. PVC conduit uses an internal spring.
Worked example. Bend 15 mm copper tube to 90° with a lever bender. Mark the bend centre, subtract the bender's take-up, clamp, apply steady pressure over the former, and check square with a try square. Reasoning: the take-up matters more than the angle - a correct 90° bend in the wrong place is still a reject.
Traps that cost marks
Threading without oil (torn threads); cross-threading the first turn instead of starting by hand; excess PTFE splitting the socket; soldering a pipe that still holds water.