Welding Basics, Part 5

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Submitted Article
Welding Basics, Part 5
Oxy-Acetylene Torches
by Curtis Von Fange

Links to the previous welding articles:
  • Welding Basics, Part 1
  • Welding Basics, Part 2
  • Welding Basics, Part 3
  • Welding Basics, Part 4
  • My favorite tool in my arsenal of welding stuff is the cutting torch. It seems that whenever I get into a difficult situation the cutting torch comes running to the rescue. The versatility of this tool is amazing. It can be used for making tools, freeing stuck nuts, heating and bending things to fit, not to mention the regular cutting of steel parts for fabricating and repairing things. The cutting torch is indeed a universal tool in the field of welding.

    Put simply the cutting torch is like a whole bunch of regular gas torches all bundled into one. In addition there is a single, large orifice in the center of the tip that delivers pure oxygen to the weld when actuated with the cutting lever. This oxygen, under the proper circumstances, will immediately oxidize the pre-heated metal and, put simply, make it disappear. Let's take a quick look at how this really works.

    As mentioned the cutting torch assembly is rather similar to the oxy-acetylene torch. In fact many torches have interchangeable ends, which makes the changeover from a welding torch to a cutting torch a quick and easy swap. For our purposes the torch base, hoses, regulator gauges, valves and tanks are the same for welding and cutting. The safety procedures and equipment are also the same and should be thoroughly checked before using the unit. The main difference between the torches is that the cutting torch attachment has an additional oxygen pre-heat valve, an oxygen-cutting valve with cutting lever, and a different type of configuration in the gas delivery and flame expulsion, and a multi-ported tip. To put it all in simple terms the acetylene gas flow is still controlled in the same location as the welding torch. But the oxygen control has moved from the lower valve to a new position up farther onto the body of the cutting torch assembly. When using the torch this lower oxygen valve is opened all the way while the 'new' upper valve is used to control the throttling or neutral flame control setting required for operation. The oxygen- cutting lever, now under full pressure through the lower valve, is used to deliver a blast of pure oxygen at the appropriate time to the metal we are cutting.

    The settings, as with regular gas welding, are determined by the thickness of the metal that you want to cut. A typical example for cutting 3/8 inch to 3/4 inch steel would be the following: a preheat orifice drill size of 58, a cutting orifice drill size of 62, oxygen pressure of 30-40 psi, acetylene around 5 psi. The multi-preheat flames, as with the single welding flame, need to be ignited with a sparkler and set to a neutral flame using the same techniques described in our previous series. Give visual consideration to optimizing the neutral flame as an oxidizing flame will be harder to work with.

    The real key to cutting metal with a torch is to always heat the working metal to cherry red. If the metal is too cool it won't cut. If it is too hot, as in white hot, it splatters, undercuts, and reduces the quality of the cut. Laying the base metal on a pair of vee blocks or steel spacers will help facilitate the cutting process. Preheat the metal edge to a dull cherry red using the tip of the multi-flame cones for maximum heat. A tight circular pattern over the starting area will even out the preheating. When a small cherry red dot appears apply the oxygen cutting valve lever. The metal will blow away like a stream of butter as the oxygen oxidizes and melts the metal in contact with the high pressure stream of gas. While holding a vertical attack angle slowly follow the melt line with the torch until the cut is complete. Prescribing the cut line with welders chalk makes following the cut line a lot easier.

    As with anything once the basics are understood practice makes the best teacher. With time (and a good piece of chalk to mark your cutting lines) further skills can be realized. One of these skills is being able to fabricate parts for repairs. Many times, such as our bushog, a piece of plate steel has to be cut and fit over a cracked section or hole in order to make the repair. The cutting torch is ideal for making these custom fabrications. By chalking the lines of the desired filler piece on a section of steel the cutting torch can make exact repair plates of virtually any type and size. With additional time and skill one can also learn to make angle cuts with the torch to create a pre-cut chamfer in the plate for stronger welds. After the cuts are made the magic of a hand grinder can make the plate look like a factory part.

    One great feature of the torch is that it can be used to make stuff fit. By heating parts to cherry red they can be bent and tweaked to various angles. Support rods or plate reinforcing can be bent to mate perfectly to matching parts. Rebar can be bent to perfect and tight 90-degree angles for support cages. Plates that have to be placed over obstructions can be heated and tweaked to have bumps, ridges, or chamfers in them. When heated to the right temperatures it is amazing to see just how pliable steel becomes. Steel tubing can be filled with sand, heated, and then gradually bent to strange angles. Done slowly and with care the pipe integrity will not be sacrificed.

    Sometimes in the shop one can run across a huge nut or bolt that requires an expensive wrench to remove. A piece of scrap steel, some carefully scribed chalk lines, and a steady torch hand can create a make-shift wrench that will comfortably work. Of course you will probably have to do some grinder touch up work on your new tool addition before it will fit close enough to use. In addition the working end can be roasted to cherry red and quenched in some water to obtain some tempered features.

    Frequently one will run across a nut that won't budge with a well-fitted wrench. Even a pipe extension, commonly called a cheater bar, wont crack it free. By taking our torch and heating the nut to our famous cherry red it will usually break free with only the effort of our wrench. Granted you might have to install a larger torch tip to release the amount of heat needed to toast that much steel. But it is amazing to see what a little heat can do on stubborn nuts. The key is to heat only the nut cherry red so it expands over the stud. On most stuck nuts there is a layer of rust between the bolt and nut that has caused the seizure. This layer can act as an insulator and retard the transfer of heat to the stud. If the nut is heated too long then the stud will also receive too much heat, start to get red, and then probably snap off when torque is applied. Focus the heat only on the nut and, when it releases and starts to turn, get it off quickly. If it seizes up again reheat it back to red and try again.

    Sometimes it is a stubborn bolt that is stuck in a component. Try heating the surrounding metal and then backing the bolt out with a wrench or vise grips. Be especially careful if it is a cast iron component. It is recommended that drilling and using an easy-out first be tried as cast iron can do strange things if too much heat is applied. In a case of a broken stud in an engine block sometimes the stud can be heated cherry red, then quenched quickly with some ice wrapped in a rag. The sudden temperature change can sometimes break the rust layer free and give some space to rotation of the stud. If all else fails a very small torch tip, a steady hand, and nerves of steel can sometimes be used to cut a problem stud out of a cast component. This last gasp tactic is best reserved for the experienced.

    All in all the cutting torch is one of the most universal and versatile tools in the arsenal of the home repairman. Make sure and keep it clean and tidy so it will be ready to serve when most needed.

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