Choosing Your Torch Tip and Pressure

When you are planning to cut steel with an oxyacetylene torch – one of the primary functions of this implement, since the flame of these torches is admirably suited to slicing through ferrous metal – then you need to make use of a torch tip of an appropriate size for the thickness of metal you are about to cut. You will also need to adjust the pressure of both the oxygen and the acetylene as it flows through the hoses and out the welding gun.

Interestingly enough, the upper limit on the metal thickness that can be cut by oxyacetylene torches is determined by the fact that acetylene cannot be pressurized at more than 15 psi, since at this point its stability begins to lessen and the chance of a random explosion, triggered by nothing more than the pressure itself, begins to rise sharply. Since more and more acetylene pressure is needed to cut thicker and thicker pieces of metal, it becomes impossible to use acetylene to cut through metal after a certain point – well beyond the thicknesses you are likely to be cutting, however.

•    For 1/8” to ¼” steel, use either a size 000 or a size 00 torch tip. The lower thicknesses need around 20 psi of oxygen and 3 psi of acetylene, while the thicker need 25 psi of oxygen and 5 psi of acetylene. You will be able to cut between 20 and 30 inches per minute, leaving a kerf (the gap left by cut away material) of .04” to .05” with your efforts.

•    A size 0 torch tip is appropriate for all steel in the 3/8” to ½” range, and a slightly higher oxygen pressure is needed. For 3/8” steel, use 25 to 30 psi of oxygen, while ½” steel needs 30 to 35 psi. Acetylene pressure is the same as for the thinner steel, from 3 to 5 psi for both thicknesses. 20 to 28 inches per minute is the typical expected cutting rate, while the kerf is close to .06” for all the steel in this range.

•    When dealing with ¾” to 1” steel, a size 1 or 2 torch tip is ideal. Oxygen cutting pressure for ¾” steel is 30 to 35 psi, while that for inch-thick plates is 35 to 40 psi. Acetylene pressure should be a touch higher in most cases, with 3 to 6 psi being the accepted range. You will discover that you can slice this steel at a rate of 15” to 21” per minute, while the kerf will vary from .07” to .09”.

•    2” to 3” steel is much slower to cut, ranging from 9” to 15” per minute, and begins to fall into the category of painstaking efforts. Use a size 3 or 4 torch tip to cut steel of this thickness. Oxygen pressure ought to be set at 40 to 50 psi, with the lower range used for 2” steel and the upper for 3”. Acetylene is fed in at a pressure of 4 to 8 psi for 2” steel and 5 to 11 psi for 3” steel.  Kerfs measure .11” or .12”.

•    For steel 4” to 6” thick, use a size 5 or 6 torch tip, which create a .15” kerf. Oxygen pressure should be set at 45 to 55 psi for both sizes of torch tip and both steel thicknesses, while the acetylene’s pressure should be 6 to 13 psi for 4” steel and 8 to 14 psi for 6” steel. 4” steel can be cut at a rate of 8” to 11” per minute, while 6” to 8” per minute is the best rate that can be hoped for from 6” steel.

•    For 10” to 12” steel, you should make use of a size 7 or 8 torch tip. Cutting 10” steel requires 45 to 55 psi of oxygen and 10 to 15 psi of acetylene, and can be accomplished at a rate of 4” to 5” per minute, leaving a .34” kerf. Cutting 12” steel can only be done at a rate of 3” to 5” per minute, using the same gas pressures, and leaves a massive .41” kerf.