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Thread: cost of cutting

  1. #21
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    Since Wombat2go has provided a reasonable formula dian can adjust to suit local conditions in search of his answer, I'll post about a few ancilliary subjects.

    The substitution of propane in place of acetylene is something I only became aware of in recent months. Despite a lifetime in proximity to all sorts of metal joining/cutting processes, I was surprised when a local commercial iron work sculptor told me he relies on oxy/propane, instead of O/A. The lower cost of propane is important, given the extensive amount of fuel required to heat & form the large scale wrought iron pieces he produces.

    As for plasma. While the process has several savings & benefits, it also has costs & limitations. I'll just limit myself to pointing out that the capacity to cut 3/4"+ material w/ plasma probably begins to exceed the means of the typical HSMer. The basic oxy/act rig is capable of a good deal heavier cuts. O/A is more portable, too - not tethered to an electrical source.
    “You learn from mistakes, but success gives you the courage to go on and do even more. ”

    ― Christiaan Barnard

  2. #22
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    Quote Originally Posted by garyhlucas View Post
    I think the oxygen lance contains aluminum rods if I remember correctly.
    thought it was magnesium. I think it was called a burning bar.
    I

  3. #23
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    Quote Originally Posted by Willy View Post
    Andy have you thought about using propane in conjunction with the oxygen? As you say it comes in darn handy as a quick source of heat for a number of applications, also darn handy for use in brazing and silver soldering.

    I used to use an O/A torch setup a lot for cutting metal then switched to propane to cut costs. However I can't remember using to cut metal for a long time. Between plasma, air and angle grinder zip wheels, and a cordless Sawzall I just can't think of a good reason why I need the cutting torch very often.


    The idea has crossed my mind as I also have tanks and tanks of propane around here for the camper, grill, and whatnot. But I still haven't had that big of a need for it. If I were getting stuck in jobs and multiple times because I needed a torch I might. But that very rarely happens especially now that I have the plasma cutter as I don't have the need to cut anything with a torch now.

    I don't solder unless it is electrical and I haven't brazed since school.

    Another reason is I don't have much room in the shop.
    Andy

  4. #24
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    Quote Originally Posted by Illinoyance View Post
    thought it was magnesium. I think it was called a burning bar.
    I
    The 'rods' in a cutting lance are iron, these are typically used to cut large cross-sections of metal. They are also used to cut concrete... body armour is highly recommended. :>)

    Industrial flame cutting can use the oxy-propane or acetylene preheat to begin the cut, once the burn is started the pre-heat gases are turned off.

    The oxygen lance of a cutting torch is sufficient to cut the entire profile as long as the correct travel rate is maintained. Since this is usually done with a mechanism of some kind, the correct travel rate rate is easy to maintain. This type of cutting is cheaper and on heavy sections the preheat flame will not cause 're-welding' of the surface next to the torch. It is technically possible by hand, but is near impossible to turn off the preheat and continue cutting on any hand torch I have ever used.

    Amaze your friends and neighbors on sheet metal. Heat the sheet metal with a welding tip, and then turn off the acetylene and cut away. You will need to practice a bit before showing off. It's a poor man's plasma torch.
    paul
    ARS W9PCS

    Esto Vigilans

    Remember, just because you can doesn't mean you should...
    but you may have to

  5. #25
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    I bought a piece of steel at the scrap yard 36” x 60” x 4” thick. A local welding shop used an oxy-acetylene track torch to slice it into 4 pieces 60” long. The cuts were amazingly square, straight, and smooth. Used them as outriggers for a crane.

  6. #26
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    Making a single cut and putting a cost to it is going to be difficult.
    One of the things that never gets mentioned or even considered is charging of the lines on a torch set. 25 footers are not a big deal. 100 footers on the other hand, you will use almost as much gas charging the lines as you do to make that 10 inch cut. Then you turn off the tanks and dump the gas to the open air. Big waste. There are better torches that do a fine job cutting, that don't consume as much gas. The Henrob/ Cobra 2000 torches do a suprising job and use half the gas. So that is a consideration.

    As far as the cut.
    Is this a one and done cut or are you going to be doing alot of this?
    If it's a one and done, who cares how much gas it consumes. If you are going to be doing this as a production thing, then you need to consider more than just the gas cost. There are more variables to the cost of gas cutting.
    What surface is required after the cut? Will there be a lot of grinding that is a labor cost. What is you kerf cost? By this I mean if your steel is 31 inches wide and your kerf is .375 inches, your 3rd plate will not be 10 inches wide.
    There are again better, but more costly methods than a gas torch , but if you are scrapping a lot of steel because the method you are using is creating scrap that a different method would save, then you tool up for the better method.

    You need to consider every part of the method. Gas consumption is only one consideration. You have cut time, prep time, cleanup (grinding) as far as labor. There is the consideration of not only gas consumption but refill requirements, and availability of a refill and the time that takes. A plasma cutter requires electricity and compressed air, and consumables. A band saw will require different power and blades which will vary in cost depending on the material being cut. You also need to figure out what resources you have where you are doing the cutting. IF you don't have electric, then a torch is it. Other than a Partner saw. ANd of course that's noisy and consumes gas. And is not a good option in a building due to fumes.

    I know this seems like I am making a simple 10 inch cut into a huge deal. But like I said before, if this is a one and done, why do you care what it costs. If you are concerned with cost, it's most likely not a one time thing. So consider ALL the costs for each method and the pro's and con's of each.

  7. #27
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    Sep 2005
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    Late to the party here, I looked at the ESAB pdf and it's very good.

    I use Koike tips, and they have a very good set of charts for each tip, with
    thickness recommended, travel speeds, and flow rates.
    So you should be able to rough calculate the cutting gas's usage.
    Preheating needs a little Kentucky Windage to add in cost's.
    Not as detailed as the ESAB booklet though.

    Allot of hearsay and just wrong info on some of these threads.....

    Just to explain the process a wee bit more, some larger machines (that cut 1"
    and thicker) have a "5 regulator" set up:
    1. Preheat fuel
    2. Preheat Oxygen
    3. Cut oxygen
    4. In-Cut Preheat fuel
    5. In-Cut Preheat oxygen

    One 1" and thicker, the travel speed is very slow, and the preheat is set very high
    (to get started on thick, cold plate)
    Once the cut is started, the preheat flames are too high, and tend to melt over
    the top edge of the part.

    To reduce this, the 5 regulator set up is employed.
    After the cut is started (the cutting oxygen is flowing) the control box
    switches off #1 & #2, and turns on #4 & #5, these are preset at a lower flame.

    Enough preheat to keep the cut going, but lower to help eliminate round over.
    EDIT: The above linked ESAB document cover it well.

    Why the inquiry in the first place ?

    I have a CNC cutting machine, and yes, I run propane.
    Last edited by digger_doug; 08-17-2018 at 02:49 PM.

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