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Old 09-05-2009, 06:21 PM
Fawteen Fawteen is offline
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Default Welding FAQ - Gas Welding

In general, there are 4 major approaches to welding: Gas, MIG, Stick and TIG. Eventually, I'll post a separate thread on each process.


Gas Welding


A gas welding rig consists of an oxygen bottle, a fuel bottle (either acetylene or propane) regulators for each, hoses, a torch handle and torch tips. Torch kits, consisting of everything but the bottles, are widely available in a wide range of prices. For the home shop and occasional use, an entry level kit will do just fine. You should be able to get into a decent kit for around $175-$200 new. Most kits will come with one or two welding tips and a cutting tip with 2 or 3 different sizes of tips for cutting different thicknesses.

The next consideration is bottles: buy or lease? The answer will vary from state to state and will require a little research on your part. In my state, the big outfits will not refill bottles they do not own, due to liability issues. I have my bottles on a 5 year lease. That's a fair chunk of change up front, but MUCH cheaper than leasing year-by-year. If you choose to buy bottles, bear in mind that most places will require that the hydrostatic test be current before they will fill them, and having the test done is not cheap. With leased bottles, I can go to a depot and swap empties for fulls and be in and out in 10 minutes. If you're having your own bottles filled, it may be a case of drop them off and come back in a couple of days and pick them up.

Another consideration is bottle size. Many folks are tempted by the back-pack kits. They're small, easier to store, and cheaper to buy. However, they are much more expensive in the long run. It costs nearly as much to fill a back-pack sized bottle that will last for an hour or two of welding time as it does to fill a full sized bottle that will run for days. It's an individual decision, based on your budget, how much room you have in your shop, and how much welding/cutting you expect to do.

Finally, you need to think about fuel choice: Acetylene or Propane? Propane tends to be more commonly available and cheaper to buy. It requires different regulators and torch bodies and they are not interchangeable with acetylene. Also, you'll burn more propane for a given amount of work than you would using acetylene. Depending on the price of propane in your area, it may pencil out better to use propane than acetylene.

The benefits of acetylene are more heat value and regulators and torches are commonly available. Drawbacks are that acetylene is usually more expensive and requires special handling. An acetylene bottle contains a porous filler, and the acetylene is dissolved in acetone and held under pressure in a liquid state. It expands into a gas when drawn off via the regulator. This creates two potential problems if not used properly: First, NEVER use an acetylene bottle in any position but vertical. If the bottle has been transported on it's side, it's best to wait several hours before using it. If you violate this rule, you're taking a chance of drawing acetone out of the bottle with the acetylene and the resulting explosion will be quite spectacular, not to mention life-threatening. The second rule is: Size your bottle, regulator and torch to the job. Drawing acetylene at a rate of more than 1/7th of the bottle's capacity per hour can also lead to entrained acetone in the gas. Again, BOOM! Unless you're cutting really thick metal or running a big rosebud, this will not normally be an issue.


Okay, so we've bought ourselves a torch kit and obtained a full set of bottles. Read the instructions. There's any number of ways to get hurt when welding and the instructions will cover most of them.

When hooking up the regulators, crack the valve briefly to blow any crud out of the connection. This is particularly important on the Oxy side. Oil and Oxygen don't mix. If your connection or regulator are contaminated with oil, an explosion or at least a very brief, intense fire is a distinct possiblity when pure oxygen is introduced.

The oxygen and acetylene regulators are NOT interchangeable, and one (I forget which) is left-hand threaded to avoid messing up.

With the regulator, hoses and torch attached, open the valves on the bottles. Two things to watch for here: Do NOT stand directly in front of the regulator when opening the valve. A weak regulator can self-destruct rather spectacularly when hit with 2000 PSI, and if it goes, it's going to launch the parts out the front. Second, don't open the bottle more than a half turn or so. It won't increase the flow, and if you need to shut it off quickly for some reason, the fewer turns the better.

For most welding and cutting operations using acetylene, an acetylene pressure of 5-7 PSI and and oxygen pressure of 20 PSI is a good starting point. NEVER set the acetylene pressure above 15 PSI. It's that old acetone/BOOM! thing again.


With the regulators set, crack the acetylene valve on the torch (red hose) and light it with a striker. Adjust the valve for a steady flame about 1/2" long. You'll see a lot of soot/carbon floaters until you get the oxy mix right.

VERY SLOWLY, crack the oxy valve. If you open it too quickly, you'll get a POP! and the flame will go out. Adjust the oxy until you see a very sharp, clear two-stage cone of fire: A small, yellow-orange cone in the center, and a larger blue-white flame on the outside. As you adjust the oxygen, you'll see the flame go from "soft and fuzzy" to "sharp and clear". This is what's known as a "neutral flame" and is a good starting place for both welding and cutting.

You'll need bump the acetylene up after initially opening the oxy enough to get rid of the soot. Keep adding acetylene and adjusting the oxy for a neutral flame until you have a hot enough flame to go to work. This will depend on the thickness and type of materiel, and whether you're brazing or welding.

With the flame adjusted properly, bring the flame to the work. The very tip of the blue portion of the flame will do all the work. If you get the torch tip too close to the work, it'll go POP! and likely blow out. If that happens, CLOSE BOTH VALVES AND START OVER. Relighting a torch with the valves adjusted for welding is not a good idea.

Hold the flame in in place until you see a puddle form. The
steel will get very shiny just before it melts. If you're working with very thin metal, it's a good idea to watch for the shiny stage and start moving the torch before you blow through.

Having established the weld puddle, you now move the torch slowly in the direction of weld, adding filler rod as necessary to fill the joint. I like to use a tight, circular motion to keep the back of the puddle hot while moving the "front" of the puddle, pointing the tip of the torch in the direction of travel.

Filler rod should be matched to the work, but for mild steel, old coat hangers work pretty darn good, and they're free. Gas welding works best in a flat, horizontal position, but with practice "out of position" welding can be done too.


Cutting is much the same as welding as regards setup. Regulator pressures are usually the same, unless cutting very thick metal. A different torch head is used that has two extra controls: A separate oxy knob for setting the cut flow, and a trigger or paddle for starting the cut.

You'll look for the same, neutral flame when lighting the torch. Once you have the flame, place the tip where you want the cut to start and begin pre-heating the metal. Once the metal has started to melt, you can hit the cut lever and let the oxygen blow a hole in the metal to start the cut. Two things that trip up most beginners are not pre-heating enough (either too little time on target or not enough heat) and the assumption that "If some oxygen is good, more is better!" It's the heat that cuts the metal, the oxygen just blows it out of the way. If you're having trouble getting a clean cut, often more fuel is the answer
rather than more oxy.

Other "tips" (har, har) on cutting are:

Sizing the tip to the job. Thicker metal requires more fuel, which requires bigger orifices in the tip.

Keeping the tip clean. Your kit will come with a tip cleaner. Use it.

Keeping the tip out of the cut. Splattered metal will clog up a tip and mess up the cut.

Replacing worn tips. Once the end of the tip gets banged up enough to distort the orifices, it won't cut as well. Tips are relatively cheap, replace them.

Signs of a worn out tip are difficulty cutting and frequent blow-outs or popping back.

Last Comments on Gas Welding

QUite frankly, I don't do a lot of gas welding. There are just too many easier ways to get it done. However, if you can only afford one piece of equipment, an O/A torch rig is the one to have. It'll weld, cut, heat-and-bend, free rusty bolts, and do a host of other things an electric welder can't do.

One last gas-welding trick: Annealing aluminum. If you've ever tried to make a sharp bend in aluminum, you know it has a nasty tendency to crack. However (and I learned this trick watching Orange County Choppers...) if you anneal it first, you can put a 90 degree bend in a piece of 1/8th inch aluminum. What you do is adjust for a very "soft" flame that actually leaves a film of soot when you apply it to the aluminum, and then heat the entire area to be bent. This soft flame will not melt or damage the aluminum, but it takes the brittleness out of it and makes it very easy to bend.
Old 09-05-2009, 06:41 PM
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Kaptain Krunch Kaptain Krunch is offline
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Man that was fast, very well written too!
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Old 09-05-2009, 06:57 PM
Fawteen Fawteen is offline
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A couple of edits upon re-reading:

1. Crack the valves to blow the crud out BEFORE screwing the regulators in, just in case that wasn't clear.

2. When you're done welding, turn the valves on the bottles off, open the valves on the torch handle to clear the gas out of the hoses, then shut the torch valves and back the regulators all the way out. Leaving the regulators preset shortens their service life and makes them prone to "taking a set" at a given pressure. Leaving gas in the hoses is a fire hazard.

3. I expect most torch kits these days come with back-flow preventers built in, but double check. Without them, a blowout on the torch can send flame back up the hoses and trust me, you do NOT want to go there.
Old 09-05-2009, 08:58 PM
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Old 09-06-2009, 12:06 AM
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Good stuff!
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