Oxy-Acetylene Cutting: What You Need and Safe Set-Up

An oxy-acetylene set heats mild steel with a flame of oxygen and acetylene, then a jet of pure oxygen burns through the hot metal. It does not cut stainless steel or aluminium; use a plasma cutter for those. Here is what a complete set needs, and how to set it up and use it safely.

What a cutting set needs

• An oxygen cylinder and an acetylene cylinder, kept upright and chained. (Ask us about cylinders.)
• An oxygen regulator and an acetylene regulator: one for each gas. They are not interchangeable.
• Flashback arrestors on both regulator outlets, and ideally on the torch too. They stop a flame travelling back into the hoses and cylinders.
• Twin hose, usually red for acetylene and blue or green for oxygen. Fuel-gas fittings usually have left-hand threads.
• A cutting torch, or a cutting attachment on a welding torch handle.
• Cutting nozzles in the sizes for the steel you cut: a bigger nozzle for thicker steel. Nozzles are made for one fuel, acetylene or LPG, so use the type that matches your gas. See the WeldRo and Murex nozzle sizes.
• Gas cutting goggles of the right shade, leather gloves, and a spark lighter. Never light a torch with matches or a cigarette lighter.

Setting up, step by step

1. Chain both cylinders upright, away from heat, sparks, oil and grease.
2. Stand to one side and open each cylinder valve for a moment, then close it, to blow out any dust. Do this away from any flame.
3. Fit each regulator to its own cylinder, then the flashback arrestors, hoses and torch. Tighten with a spanner, firmly but without force. Keep oil and grease away from every oxygen fitting.
4. Turn both regulator adjusting screws out until they are loose. Open the cylinder valves slowly: the acetylene valve no more than about one to one and a half turns, with the key left on it so it can be closed quickly.
5. Set the working pressures from the nozzle maker's chart for your nozzle size. Never use acetylene above 1 bar (15 psi): above that it can become unstable.
6. Check every connection for leaks with soapy water, never with a flame.
7. Purge the hoses: in open air, away from flames, open each torch valve in turn for a few seconds, then close it.
8. Open the torch's acetylene valve a little and light it with the spark lighter. Then open the oxygen slowly until the flame is neutral, with a sharp, clear inner cone. Press the cutting lever to check the oxygen jet.

Making the cut

Hold the nozzle a few millimetres above the steel and heat the edge until it glows bright red. Press the cutting lever and move along the line at an even speed: too fast and the cut stops; too slow and the edge melts and rounds over.

Shutting down

1. Close the torch valves in the order the torch maker gives; most say acetylene first, then oxygen.
2. Close both cylinder valves.
3. Open the torch valves again to empty the hoses, close them, and turn the regulator screws out.

If the flame pops or hisses

A pop with the flame going out is a backfire, often caused by a dirty or overheated nozzle, or the nozzle touching the work. A squeal or hiss with the flame burning back inside the torch is a flashback: close the torch's oxygen valve at once, then the acetylene valve, then both cylinder valves. Let the torch cool and have it checked before you use it again.

Safety basics

• Never let oil or grease touch oxygen fittings, and never use oxygen to blow dust off clothes or the work.
• Keep a fire extinguisher close, and cut away from anything that can burn.
• Cut with good ventilation.
• Close the cylinder valves whenever you stop work.

What to tell us when you order

• The thickness of the steel you cut
• Your fuel: acetylene or LPG
• Whether you already have cylinders, regulators or a torch

General guidance only. Always follow the manufacturer's instructions for your machine, gas and electrodes.