A Complete Guide on How to Use a Cutting Torch
Welders, plumbers, and metal fabricators know it well. A cutting torch, also known as a blow torch, is a blowpipe whereby metal is preheated using fuel gases and oxygen in order to cut materials.
When cutting, a metal if first preheated with a flame then oxidized by pressing an oxygen blast trigger. While the process sounds easy in the paper, many people find it difficult and dangerous to make accurate cuts.
It takes proper settings, a safe work environment, and carefully monitoring pressure to make quality cuts. Besides, the proper use of an oxy-acetylene torch guarantees safe operation.
Before you start using a Cutting Torch Read How to Choose The Best Cutting Torch for Soldering
Now, let’s take a closer look on how to use a cutting torch.
Table of Contents
- 1 How to Use a Cutting Torch
- 2 Cutting torch-tips tricks
- 3 How Do You Set Up an Oxy-Acetylene Torch?
- 4 What do you turn on first oxygen or acetylene?
- 5 What do you turn off first, oxygen or acetylene?
- 6 The ratio of Oxygen to Acetylene
How to Use a Cutting Torch
- Put on your safety gear before lighting the torch. You need to be extra careful as this process is powerful and dangerous at the same time. Also, check your working area of any flammable materials.
- Using a striker, light the torch and slowly open the acetylene valve first. This allows oxygen to purge and prevent expulsion. Now shut the acetylene valve tight. Then press the handle while holding the striker direct the torch tip. Don’t use a match lighter as the process is dangerous.
- Once you notice a yellow flame, make adjustments to the valve. The flame should be around 10” long. Ensure the yellow flame lights at the tip of the cutting torch. Keep the flow of acetylene stead to avoid jumpy flames that may increase the risk of an injury.
- Once this temperature is attained, the next step is turning on the oxygen valve positioned on top of the torch. Similar to the acetylene valve, turn it forward slowly. The yellow-colored flame should turn to blue as oxygen is gradually released to fully burn the acetylene. Now increase oxygen supply to the point the inner blue flame starts to shrink.
- To increase the size of the burning flame, adjust the oxygen valve forward. To know if you got it right, the size of the flame should be more than the thickness of the metal cut. Let’s say, if the inner flame is about 1.8cm, the steel should be about 1.0cm. If you notice the flame is getting irregular and feathery with a lot of wafting noise, then it means the oxygen supply is too much. Adjust until the blue flame stabilizes.
- Move the blue inner flame close to the surface you intend to cut. You don’t have to place the flame directly on the surface. Now heat the metal until it turns to liquid iron oxide and luminesces at this point. The cutting torch only heats the metal and further heat is supplied by the burning steel. Keep the tip of the torch stable from the steel’s surface to concentrate the heat in a specific point. For steel measure 0.5 inches, it will take an average of 45 seconds. Heavy and thick metals will take a longer time.
- Push the oxygen cutting jet level all the way until the molten steel is ignited. An instant violent reaction indicates the steel is already ignited. Now increasingly adjust the pressure to the point the cutting jet goes through the steel metal. In case there is no reaction, then open the oxygen valve and allow the flame to heat the meal enough in order to ignite.
- Start moving the jet gently along the line of cut. The molten slag should be blown out through the back of your cut. In case the flow of these materials slows down, stop advancing, and allow the metal to heat up. It’s recommended to cut slowly than doing it rapidly.
- If heat is enough, continue the process until you complete the cut. Ensure the molten pool or slag does not find its way to your underfoot. Even if you are wearing safety boots, the molten pool can burn through them.
- Once you are through cutting, now turn off the acetylene torch. It’s simple, just reverse the process you started with. First, turn off the fuel gas torch valve. Then, turn off the oxygen. Never turn off the oxygen first as large flames may rise and burn the equipment. Next is turning off the cylinder valves. Purge the pressure inside the oxygen tanks by releasing the torch valves one a time. Go to the regulator pressure and repeat the process for the acetylene line. Close the valves!
- Use cold water to cool the heated workpiece. However, never do this in a hurry as the superheated piece is likely to form an instant cloud of hot steam. You don’t want to know what will happen in case the steam comes into contact with your face. Alternatively, allow the workpiece to cool naturally.
Cutting torch-tips tricks
Making a proper and clean cut using a cutting torch is a matter of using the right pressure settings, having the right size tip and a stable hand. Once you master this, then you are good to go. I have compiled a list of tricks on how to make a clean cut with a torch. Get them right and your cuts will be super accurate and clean.
- Use a mixture of soapy water to clean the connections. It’s safer to use water than oil or grease. Even without a flame, pure oxygen is likely to burn once it gets into contact with oil.
- Stand aside when releasing the cylinder valve. This safety precaution will help you avoid any mishap as the regulator is likely to force the gas towards the bonnet in the event it fails. The acetylene valve should open only halfway while the oxygen cylinder full way.
- Crack the valves before opening. To prevent dust and foreign materials from getting inside the regulator, always crack open the cylinders slowly. Do it slowly and allow some gas to escape then tightly close it. Any foreign contaminants in the valve are blown out.
- Leak test. Always check for leaks before lighting. A liquid leak detector does better. See if there are any growing bubbles to know when there is a leak. Now, use a wrench to tighten all connections
- The key to having good quality cuts is using the right tip size. You can use a tip chart to help adjust the right gas pressure. Also, flow rates vary depending on the brand. Always refer to the tip chart for the right tip size.
- Pressure drop. Gas pressure will when using long lengths of the hose before reaching the torch. Check pressure drop charts at Smith cutting torch pressure settings. Increase the regulator delivery weight in order to compensate for the drop. This way, the back of the torch pressure is able to deliver the right cutting tip.
- Cutting torch gauges. Check the precise pressure for rig when regularly cutting at lengthy distances from the cylinders. The cutting torch gauges should match the desired pressure.
- Use your free hand to support the other cutting hand. To perfectly achieve this, brace the free on a piece of the material.
- Always ensure the metal attains its kindling point before you can pierce it with a cutting flame. Check the temperature by slightly releasing the cutting oxygen lever. The burning flame should also turn yellow to indicate the lighting point. Fully depress the lever in case the metal instantly forms hard slag. You can as well depress the cutting lever and keep the preheat flame for some time.
- Start piercing from the center and move outward in a spiral direction to the cutting path.
- Keep in mind the torch height when cutting. You should hold the torch in a manner that allows the inner blue flame to stay off the surface you intend to cut. Besides, alternate fuels tend to be highly tolerant when it comes to torch height.
- For beginners, you might find it hard to light the torch in the initial stages. The trick is simple. Just hold the torch against the plate at an angle of 45 degrees. The plate will help trap the gas. Once lit, avoid using preheat oxygen as it’s likely to turn off the flame. Just hold the tip of the oxy-acetylene torch at 45 degrees and gradually release preheat oxygen to the point the flame stabilizes.
- I will repeat this as many times as possible, always shut the oxygen valve first then the gas fuel. The reason is to check for any leaks when turning off the torch. A dim flame at the end of the cutting torch means there is a fuel leak. Equally, a sudden pop sound is an indicator of a leaking oxygen lever.
How Do You Set Up an Oxy-Acetylene Torch?
An oxy-acetylene cutting torch is designed with a variety of mechanisms that must be properly set up. That way, you minimize the risks of mishaps and ensure a smooth operation for quality cuts.
Below is a step-by-step guide on how to set up a cutting torch:
Secure the oxygen and acetylene tanks.
The oxy-acetylene rig is stored with the bottles facing forward. A cylinder cart can help secure them in an upright position. Alternatively, you can chain the tanks to a strong and sturdy object or wall with tie-down straps. Whether the cylinders are in use or not, ensure they are not knocked down.
Get rid of the covers protecting the tank
In case there are no covers, then ensure to remove any debris inside the valves and attach the regulators to the valves. The presence of dust on the valves is likely to cause malfunction on the torch. Wondering how are you going to do it? Simple, just stand on the opposite side of the valve and release it quickly before tightening again. This way, all the dust that might have settled on the valve gets blown away.
Attach the hoses to regulators
Before doing so, ensure the regulators have the same threads. You can use an adaptor in case there are no same threads. For safety purposes, the regulators should be tight and secure. Use a wrench to tightly secure them.
Besides, connect the hoses to the respective regulators. The red hose should be connected to the acetylene while the green to the oxygen regulator. You should never use any form of lubricant to the hoses.
Connect the hoses to the torch handle.
Fix the cutting torch to the handle and tighten it manually. The valves on the torch handle should remain closed before turning on the cylinders
Open the oxygen tank valve.
It should completely open. Now find the regulation adjustment trigger and turn it from left to right. Ensure the cutting torch gauges read around 50 psi.
Do the reverse for the acetylene tank. However, turn the valve only a quarter way to open. Adjust the regulator until the gauge reads 10 psi.
Slightly open the oxygen valve to let oxygen out. Open the acetylene valve at a maximum angle of 45 degrees.
Check for leakage. Use an approved leak detector to see if bubbles grow on the coated surfaces. You must tight the connections again before moving to the final step. Also, repeat the leak test until you confirm zero leaks.
Light the torch. Use a spark lighter to light the torch. Check the flame while using the torch. In case of a backfire, stop and relight again.
What do you turn on first oxygen or acetylene?
Everyone does differ depending on their own skills and experiences. However, the recommended way suggests turning on the oxygen valve first before the gas fuel. While the oxygen valve is opened fully, the acetylene valve is only turn on a quarter to open.
What do you turn off first, oxygen or acetylene?
For safe operation, the oxygen valve should be turned off first then acetylene. This way, acetylene blows out ay soot that might have settled on the torch. Besides, the technique allows for checking of any leakages before turning off the tanks completely.
The ratio of Oxygen to Acetylene
The right ratio of oxygen to acetylene is 1:1. Under this, a neutral flame that is blue in color is produced. This is the best flame for making quality cuts without damaging the steel.