Harris 543MX Acetylene FAQs
Acetylene cutting, welding and gouging parts for a medium-duty gas torch, with practical advice on choosing and using them.
Why do I need nozzles made specifically for acetylene?
Nozzles are designed for a particular fuel gas, and each torch should be fitted with the nozzle intended for the gas in use. Acetylene gives the hottest, most concentrated flame of the common fuel gases, which is why it is popular for short cuts, piercing and thin sheet.
A nozzle made for another fuel gas such as propane has different channel and preheat design, so do not swap them. Check the fuel gas shown in the maker's data against the gas on your torch before fitting.
What does a cutting attachment do compared with the handle it fits?
The handle, or shank, carries the gas from the hoses and holds the valves. A cutting attachment fits onto it and adds the extra oxygen route that cutting needs. A cutting nozzle uses oxygen in two ways: some is mixed with the fuel gas to feed the preheat flames, and a separate lever-controlled supply gives the cutting jet.
The preheat flame brings the steel up to temperature, and the cutting oxygen then burns through it. Check that the attachment, mixer and nozzle you choose are specified for your handle and for acetylene.
What working pressure should I use for acetylene?
Acetylene is used at low pressure on the torch side, much lower than the cylinder pressure. HSE guidance says the acetylene pressure should not exceed a low limit for most welding and cutting unless the equipment has been specifically designed for more, so do not raise it to compensate for a worn or blocked nozzle.
Set the pressures for your nozzle size from the manufacturer's data. Use only regulators, hoses and blowpipes designed and marked for acetylene and oxygen, and read the data plate and manual for anything specific to your equipment.
How can I tell if my cut is good and what should I adjust?
A good cut has a square edge, a smooth surface, small drag lines and no slag on the underside. Coarse drag lines or slag on the bottom edge can mean you are travelling too fast, and too little cutting oxygen pressure can also leave an uneven surface and extra slag. Too much preheat can melt the top edge, and holding the nozzle too high or too low disturbs the cut.
Adjust one thing at a time, starting with travel speed and nozzle height, and check the nozzle is clean, undamaged and the right size for the thickness. Set the pressures from the nozzle maker's data.