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Home Welding Knowledge Cut the Crap: Beginners Guide to Cutting with an Oxy-Acetylene Torch

Cut the Crap: Beginners Guide to Cutting with an Oxy-Acetylene Torch

by Steve Darnell
oxy-acetylene torch

Welding is actually a fairly versatile skill. It can be used around the home, in the garage, or in a professional setting. No matter your welding goals, it is important to have a firm grasp of the basics. 

Sometimes materials need to be cut or shaped. There are a few options available to welders. You can use a grinder or saw, or depending on the material you are cutting, use the plasma cutting technique. But these options aren’t always appropriate.

When cutting thick mild steel, a plasma cutter just won’t, well, cut it! Don’t have access to electricity? A grinder or saw is out of the question. And that’s where oxy-acetylene torches come in. 

Oxy-acetylene cutting can be used in a range of projects but to do it right, you need to understand the process and how to properly set up the torch.

To help you out, we’ve put together this handy beginner’s guide to cutting with an oxy-acetylene torch!

How Does an Oxy-Acetylene Cutting Torch Work?

One of the essential elements in welding is understanding the science behind what you are doing and the equipment you are using to do it. 

An oxy-acetylene torch, as the name suggests, allows for a mixture of oxygen and acetylene to combust and create a flame that can exceed 3000 °C (over 5000 °F). This high temperature makes the flame hot enough to cut through mild steel. 

Steel ignites between 700 to 900 °C (1290 to 1650 °F). At this temperature, all the components that protect the steel from oxygen will be removed and the steel will remain in a solid form. Essentially, the cutting torch is preheating the steel. Once the steel reaches that bright, cherry red color, you know it has been properly preheated.  

Now that the steel has been stripped of its protectants, the oxygen will produce an exothermic reaction (meaning it releases heat) that will cause the solid metal to become oxidized liquid or slag. Because the melting point of steel is higher than the ignition temperature, the slag can be blown away by oxygen, revealing solid steel underneath. 

As long as the cutting torch is lit and is touching the steel, this reaction will continue. Because the protective elements have been removed, and you are constantly applying heat for an exothermic reaction, a protective crust will not form. And because there is no crust, the oxygen from the torch can penetrate the exposed solid steel, and cut straight through. 

The presence of acetylene produces the highest flame which makes this method the fastest and highest quality cuts compared to other oxy-fuel cutting processes. 

What Components Do You Need to Cut With Oxy-Acetylene?

There are several components that are necessary when planning to cut with an oxy-acetylene torch. 

Here is a quick list of these components: 

  • Cylinders of both oxygen and acetylene. Oxygen cylinders will usually be painted green while acetylene cylinders are usually painted black.
  • Regulators. Oxygen and acetylene cylinders have high internal pressure. Regulators reduce that pressure to a working level and help create a consistent working pressure even as the cylinder pressure drops with use. 
  • Welding hoses. Hoses will connect your cylinder regulator to the welding torch. 
  • Check valves and flashback arrestors. These two items are important safety checks. When installed between the hoses and the torch, check valves prevent the acetylene and oxygen from feeding back into the hose or regulator and causing combustion. But, check valves can’t stop flashback once it has started. A flashback is a high-pressure flame that occurs in the hose. Flashback arrestors will prevent flashback. 
  • Torch. The torch consists of a handle, oxygen and fuel valves, and a mixing chamber. Welding tips or cutting attachments are applied to the torch based on the technique being performed. 
  • Welding and cutting tips. The tips that you will require will depend on any manufacturer’s specifications, the thickness of the metal, and the application. Consult a tip chart, like the one found here, for guidance.  

While the exact set up of your rig may vary, there are the basics required for cutting with acetylene.

When to Use Oxy-Acetylene for Cutting

Oxy-acetylene torches are only useful cutting tools in certain situations. Not all materials are appropriate for this method. 

Oxy-acetylene can be used for cutting low- to medium-carbon steels and wrought iron. Only metals with oxides that have a melting point lower than the melting point of the base metal can be cut using this method or the oxides will form a protective crust and stop the process in its tracks. 

High carbon steels are hard to cut through this method because the melting point of the slag is pretty close to the melting point of the steel itself so that the slag will mix with the clean melt near the cut. 

Oxy-Acetylene Cutting vs Plasma Cutting

Here’s a quick look at two popular cutting methods and when it is appropriate to use them. 

Materials

As mentioned above, oxy-acetylene cutting can be used for mild steel and some low alloys. Other materials may be better served with plasma cutting, especially aluminum and stainless steel.

Thickness

Plasma cutting is best for thinner materials because it would require too much energy to penetrate all the way through. Oxy-acetylene cutting can be used for materials 6-12 inches thick up to 20 inches. 

Cutting angle

Plasma cutting is limited to a 45-degree travel angle, if the angle is any steeper, the plasma beam will start to deflect. When cutting with oxy-acetylene, the angle can be as steep as 70 degrees, allowing a little more flexibility in the project.

Costs

Oxy-acetylene cutting is less expensive than plasma cutting. The initial investment is equipment is less and the operating costs are lower. 

Precision

Plasma cutting is great when precise cuts are necessary. It can be used on delicate materials and is better for working with shaped metals. Plasma produces minimal slag and makes cleaner cuts than oxy-acetylene cuts.

Ease of use

While the start up costs may be more expensive, plasma cutters require less set up and less post-cut clean-up. Oxy-acetylene torches are more complicated to put together but can potentially be used in more applications as they do not require electricity. Some smaller oxy-acetylene systems can weigh as little as 35 pounds, meaning you can take it just about anywhere. 

How to Set Up an Oxy-Acetylene Torch

Because there are multiple gasses involved, using an oxy-acetylene cutting torch can be intimidating. But don’t let your nerves get in the way!

While the setup isn’t necessarily straightforward, and it can take a little getting used to, it is something that can be mastered, even by beginners!

Before you get started, check to see if there are any specific or unique instructions from the manufacturer of your cutting torch. These instructions should always override any general instructions like those we are laying out below. 

Oxy-Acetylene Torch Set-Up: Step by Step

  1. Secure the oxygen and acetylene tanks in an upright position. If you have cylinder carts, use those to secure them in place. 
  2. Check and remove protective coverings from the tanks. If there are no covers, clean the tanks to remove any debris or dust. Pay close attention to the valves. To clean the valves, stand away from the opening and turn them on and off in a quick motion. This little burst should blow away any dust or debris that may have accumulated. 
  3. Check that the regulators that need to be connected to the valves have matching threads. If they do not, connect the regulator to an adaptor, then connect the adaptor to the valve. Screw them in place by hand, then tighten the connection using a wrench. 
  4. Find the hose for oxygen and the hose for acetylene and attach the proper hoses to the regulators for the proper tanks without contaminating them. Typically, the red hose will be for acetylene and the green hose will be for oxygen.
  5. Once the hoses are in place, attach the other end to the handle of your cutting torch. 
  6. Connect the torch to the handle and tighten the nut by hand. Make sure that the valves on the torch and on the handle are closed. 

Now, it is time to perform some checks before you light your cutting torch and get to work. Before you do the checks, make sure that your regulators are facing away from you!

Pre-cutting checklist:

  1. Slowly, and one at a time, open the valves on both tanks. 
  2. Adjust the screws on the regulators so the gauge reads the proper psi. You will want between 40 and 60 psi for the oxygen tank and 10 psi for the acetylene tank.
  3. Slightly open both valves on the cutting torch. But, do not open the acetylene valve more than a 1/8 turn or 45 degrees.
  4. Perform a leak test on all connected parts. To do this, use a solution specifically for leak testing or make a paste using dissolved Ivory soap. Coat the valves, hoses, and regulators. Look for any bubbles that form after a few minutes. If bubbles appear, there is a leak and you must tighten or adjust the connections. Repeat this test until no bubbles appear. 

Once all of these steps have been completed and the leak test is a success, you are ready to light the torch by following the manufacturer’s instructions. 

Important Safety Tips for Cutting with Acetylene

As with any welding or cutting process, safety should be a top priority. 

Basic safety precautions should be taken which include wearing protective clothing, like an apron or shirt, gloves, a welding helmet or mask, safety glasses, long pants, and steel-toed boots. Be sure to make sure you aren’t wearing baggy materials or cuffs. You do not want to give sparks a place to hide. 

But using an oxy-acetylene torch has its own safety considerations as well. Here’s what you need to know to keep safe and avoid dangerous situations or accidents. 

  • Never use acetylene over 15 psi
  • Never use grease on or near oxygen equipment
  • Never use oxygen or acetylene to blow dirt or dust from clothing or equipment
  • Never light the torch with matches or a lighter
  • Do not carry matches, lighters, or other flammable objects in your pocket while welding or cutting
  • Make sure adjusting screws on the regulators are released (by turning them counterclockwise until free) before opening the cylinder valves
  • Always stand to the side of the regulator when open opening the cylinder valves
  • Always have a fire extinguisher nearby
  • Always replace cylinder caps when you are finished using the cylinders
  • Do not assume cylinder contents based on color alone. Some manufacturers may use different color codes. Always read the markings. 
  • Always use the proper regulator for each gas type
  • Ensure that cylinders remain in an upright position
  • Do not store cylinders above 130℉
  • Always keep the valve wrench on the acetylene cylinder valve when in use
  • Always be aware of your surroundings when using an oxy-acetylene torch
  • Do not allow welding hoses to come into contact with the flame or sparks from the cutting

Many of these safety recommendations may seem like common sense but when you are working with flammable gases and open flames, you can never be too careful. Check and double-check!

Master the Basics with Welder 101

When it comes to welding, there are lots of different techniques you can use to complete your favorite work or home project. But when you are just starting out, it can be hard to keep it all straight. Should you be MIG welding? TIG welding? What technique is best for different metal types? It’s a lot.

But with the Welder 101 training courses, you will get over 30 years of welding experience distilled into enjoyable and easy to follow video tutorials. Enrollment in the program gives lifetime access, and with new videos being added all the time, you’ll never miss an opportunity to improve your welding skillset! 

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