Single vs Double Layer Laser Nozzles: Which to Use for Which Gas and Material

Use a single layer nozzle for nitrogen or air cutting of stainless steel, aluminium, brass and copper. Use a double layer nozzle for oxygen cutting of carbon steel, especially thick plate. That is the convention the head makers and machine builders work to, and it is the first thing to check when a cut that should be clean comes out with dross or a burnt edge. After the layer, choose the bore: larger material thickness needs a larger bore. Then match the nozzle to the head, because the same bore and layer comes in several body sizes and threads that do not interchange.

What "single layer" and "double layer" mean

Both types are machined copper cones that screw into the ceramic ring at the bottom of the cutting head. The laser beam and the assist gas leave through the same hole in the tip. The difference is inside.

• Single layer: one conical bore from the thread down to the tip. Look into the threaded end and you see straight through a smooth taper to the hole.
• Double layer: a second copper sleeve sits inside the outer body, so the gas has two layers of passages before it reaches the tip. Look into the threaded end and you see the end of the inner sleeve, often with a hexagonal or stepped shape, sitting inside the bore.

Laser equipment maker HG Star describes the double layer nozzle as having "two layers of air ports inside", giving a faster gas jet with a longer reach than a single layer nozzle. Precitec describes its own double ("duo") HP1.5 inch nozzles as ideal for thick mild steel. The outside of the two types looks the same once fitted, so the only reliable checks are the part number on the packet and a look into the threaded end.

Why the gas decides the layer

Fiber lasers cut in two different ways, and each nozzle suits one of them.

Oxygen cutting of carbon steel is an oxidation process. The oxygen burns the hot steel in the kerf and that reaction adds heat to the cut, which is why oxygen cuts thick mild steel plate that the laser power alone would struggle with. What matters is a stable, well directed oxygen stream all the way to the bottom of the kerf. That is the job the double layer nozzle is built for.

Nitrogen or air cutting of stainless steel and aluminium is fusion cutting. The laser melts the metal and the gas simply blows the melt out of the kerf. Nitrogen is inert, so the cut edge stays bright and free of oxide, which matters on stainless that will be welded or painted. Fusion cutting runs at much higher gas pressure than oxygen cutting, and the single layer nozzle with its open conical bore is the standard choice. Compressed air works the same way at lower cost, with a slightly darker edge because air still contains about a fifth oxygen.

Put the wrong layer on and the machine still cuts, but not well. A single layer nozzle on oxygen jobs in thick plate gives a less stable gas stream through the kerf, which shows up as dross on the bottom edge and rougher striations. If the cutting parameters are right and the cut is still poor, check the layer before anything else.

Choosing the bore size

The bore is the diameter of the hole at the tip, in millimetres. It controls how much gas reaches the cut and the shape of the gas column. A larger bore passes more gas, which thicker material needs to clear the deeper kerf. The general guidance published by laser machine builders such as HG Star and DXTech runs like this:

• Sheet under 3 mm: 1.0 mm bore, or 1.0 to 1.5 mm.
• 3 to 10 mm: 1.5 mm bore, or up to 2.0 mm.
• Over 10 mm: 2.0 mm and larger.

Treat that as a starting point and use the nozzle your machine builder's cutting table calls for. Those tables give layer, bore, focus position, gas pressure and nozzle height together for each material and thickness, and the four settings only work as a set. Across our seven nozzle families the bores run from 0.8 mm up to 6.0 mm, and every bore we list comes in packs of 10, all the same layer and size.

Read the layer from the part number

When the nozzles are loose in a drawer, the bore is usually stamped on the flange (a nozzle marked "1.2 H15" is a 1.2 mm bore, 15 mm tall), but the layer is not. The head maker's part number tells you both. Raytools, Precitec and BOCI each use a fixed series for single and a different one for double, with the bore in the last digits.

On the standard Raytools D32 nozzle, for example, 120GJT0515 is the 1.5 mm single layer and 120GJT0615 is the 1.5 mm double layer. On the Precitec HP1.5 inch nozzle, P0591-002-00015 is the 1.5 mm double layer and P0591-573-00015 the 1.5 mm single. Each of our nozzle listings carries a size table with the head maker's number for every bore next to our SPM number, so you can order straight from the number on the old packet.

Match the nozzle to the head, not the machine

The layer and bore are only two of the four things a nozzle has to match. It also has to fit the head: outside diameter, height and thread. A Bodor, HSG or Gweike machine can carry a Raytools, Precitec or BOCI head, and the nozzle follows the head. The families we stock show how much they differ:

• Raytools D32: 32 mm diameter, 15 mm tall, M14 thread, for the BM110, BM111, BMH114, BT240 and BT240S heads. We list it in a standard profile with 15 single and 15 double layer bores, and in a high speed stepped tip.
• D28 x H15, M11 x 0.75: the shared size used on Precitec HP1.5 inch heads, BOCI BLT heads and the Raytools BT220, BM114, BM115 and BS06K. Our Precitec HP1.5 inch nozzle and BOCI D28 nozzle each come in 17 single and 17 double layer bores, 0.8 to 6.0 mm.
• Raytools 3D: a compact 15 mm diameter, 19 mm tall nozzle with an M8 x 0.75 thread for tube and 3D heads such as the BM109TC and BD04K. The small body clears round and square tube.
• Raytools bullet (E type): a slim 10.5 mm by 22 mm tip clamped by a separate locking nut, for BT210S and BT240S heads. Its 211GJT part numbers do not follow a layer pattern, so use the size table on the listing.

For a typical stock of the two most used sizes on a Raytools D32 head, a pack of ten 1.5 mm double layer nozzles for oxygen work is see current price and a pack of ten 1.0 mm single layer nozzles for thin stainless is see current price. The full range is in our laser nozzle collection.

Fitting a new nozzle

The nozzle is part of the capacitive height sensor as well as the gas path, so a change is more than screwing on a new part.

• Switch off the laser and let the nozzle cool before unscrewing it.
• Check the ceramic ring while the nozzle is off. A cracked or loose ceramic gives height faults that no new nozzle will cure.
• Screw the new nozzle in by hand until it seats. Do not use pliers on the tip.
• Run the capacitance calibration. The Raytools BM111 manual calls for it every time the nozzle or ceramic is replaced.
• Centre the nozzle on the beam with the machine's centring routine or a tape shot, so the beam passes through the middle of the bore.

An off centre nozzle puts more gas on one side of the kerf than the other. The result is dross on one side only, over melted corners and unreliable piercing on plate over 3 mm. If those symptoms appear straight after a nozzle change, recentre before touching the parameters. Piercing throws spatter back up through the nozzle on every cut, so check the protective window at the same time; our guide on when to replace a protective window covers that part.

When to replace a nozzle

Inspect the tip at the start of each shift. Replace the nozzle when the bore is no longer round, when the tip is dented or burnt, or when spatter has fused to it and does not brush off. A worn bore changes the gas flow in the same way as fitting the wrong size, and a damaged tip upsets the height sensing. Keep spares of every bore you run, in both layers if you cut both carbon steel and stainless, so a damaged nozzle never forces you to run the wrong one.

Frequently asked questions

Can I cut stainless steel with a double layer nozzle?
It will cut, but the single layer nozzle is the standard choice for nitrogen and air cutting and gives the cleaner result at high pressure. Keep both layers in stock if you cut both materials.

How do I tell single from double when the nozzles are mixed up?
Look into the threaded end. A single layer nozzle shows one smooth taper to the hole. A double layer nozzle shows an inner sleeve inside the bore. The stamping on the flange gives the bore and height, not the layer.

Do Raytools D28 and Precitec HP1.5 inch nozzles interchange?
Both are 28 mm diameter, 15 mm tall with an M11 x 0.75 thread, so the body fits either head. Order by the part number for your head where you have it, because tip profiles differ between families.

What bore should I start with?
Use your machine builder's cutting table. Without one, 1.0 mm for sheet under 3 mm, 1.5 mm for 3 to 10 mm and 2.0 mm or larger above 10 mm is the common starting point.

Can you supply a nozzle that is not listed?
Yes. Send the head model and the part number from the old packet through our quote request page and we will source it.