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How do I make proper cuts with a torch?

Discussion in 'The Hokey Ass Message Board' started by Kevin Lee, Nov 11, 2011.

  1. Kevin Lee
    Joined: Nov 12, 2001
    Posts: 7,442

    Kevin Lee
    Super Moderator
    Staff Member

    Getting ready to notch my frame and had planned to cut the boxing plates with my torch. I've been watching videos, reading, adjusting pressures, travel speed, angles, etc.

    I can watch the flame cut fully through the material and about 1/4 to 3/8" behind the flame molten metal just collapses into the cut and fills it in. I feel like I've tried everything and no matter what gas pressure, torch (I have a couple) travel speed, metal thickness, etc. the results are exactly the same. (front and back pictured)

    Attached Files:

  2. Kevin Lee
    Joined: Nov 12, 2001
    Posts: 7,442

    Kevin Lee
    Super Moderator
    Staff Member

    I can still pop the chunks out and it I suppose it could be passable, but I've seen plenty of nearly plasma like results so I won't be happy until I can pull that off.

    Attached Files:

  3. VoodooTwin
    Joined: Jul 13, 2011
    Posts: 3,455

    from Noo Yawk

    Crank up the acetylene pressure. I use 25 on the O2, and about 7-10 on the acetylene. Cuts like butter. What does your flame look like? How close to the work-piece are you holding the tip?
    Last edited: Nov 11, 2011
  4. Kevin Lee
    Joined: Nov 12, 2001
    Posts: 7,442

    Kevin Lee
    Super Moderator
    Staff Member

    ...and here's a chunk of 3/8" to illustrate the same result. Bottom of the cut fills back in and I end up having to break it off.

    Attached Files:

  5. hammeredabone
    Joined: Apr 18, 2001
    Posts: 735


    Kevin, Is your cone sharp? When you push the lever the cutting cone should be as sharp as possible. also when was the last time you cleaned the cutting head? Is this a full size torch or mini? Seems like this has happened to me with a mini. I would use 40#on the oxy at least 15 on acetylene. Hope any of this helps reduce grinding time. Gordon
    Last edited: Nov 12, 2011
  6. AJofHollywood
    Joined: Oct 3, 2008
    Posts: 641


    Let us know what torch you are using to know if you've got the right set up.

    Because I don't know what these guys are talking about at, 40 pounds of oxy is more suited to cutting 2" steel.
  7. twenty gallons
    Joined: Jun 7, 2010
    Posts: 444

    twenty gallons

    from what I can see, you have 2 things needing attention, first is your torch tip is not clean. it needs to be clean enough that you can form a flame of clear blue CORE flame about 3 or 4" long ......and with the sheet metal you are showing us a cut attempt at, you are moving too slow. you are moving slow enough that the metal stays molten and flows back in to the cut. Personally I use about 25 to 30 lbs oxy and 10 to 15 lbs acet.
    CLEAN TIP and a steady hand is the secret to cutting fine lines..

    Anchor your left hand and pivot the cutting head in your right hand off of your left hand.
    Kind of like shooting a pistol...............
  8. Barrelnose pickup
    Joined: Aug 20, 2008
    Posts: 1,420

    Barrelnose pickup

    Knowone has mentioned cutting tip size or angle of the tip when cutting.
    Only thin material so the tip size should be around a #8 or smaller and while cutting
    try tilting the torch back at the top,that way the flame helps blow the molten metal away from the cut.Go abit quicker also,you will know when you're going to fast as the cut will stop.Good luck.
    Last edited: Nov 12, 2011
  9. It's all in the angle you hold the torch. Just like anything else, practice.
  10. Agree, clean tip, correct size for material, correct oxy pressure, nice long clear blue flame when the oxy lever is depressed and the right speed for the metal you are cutting with a nice steady hand also helps. An a shitload of patience and practice. I also have a set of cutting wheels that clamp onto the tip which keep the tip the required distance from the metal and helps keep nice steady cuts.
  11. Eric N
    Joined: Jul 1, 2010
    Posts: 10

    Eric N

    Your biggest problem is definitely speed, you're going to slow. What everyone else said about keeping a clean torch is also important.

    Also, what are you pressures set at. Some people are saying some pretty high numbers especially for the material you're cutting.

    5-6lbs on the Act and 27-30 on the Oxy should be more then enough.
  12. Eric N
    Joined: Jul 1, 2010
    Posts: 10

    Eric N

    Also, how thinck is the material you're cutting. In your 2nd post you said it was 3/8" and given that thickness speed definitely is one of your problems.

    For thinnner material, you'll also want to angle your cut away from you're good material slightly, I'll whip up a crude drawing of what I mean.
  13. You should be able to go right through that. Go faster for sure. Use your other hand as a guide like when pinstriping. Or use a 1/2 piece of steel for straight cuts or a piece of hard wood with a shape if you are not so steady. Comes out so clean. Also get the metal nice an orange,before you start to push it through. Good luck Kevin. I like your style.
  14. Eric N
    Joined: Jul 1, 2010
    Posts: 10

    Eric N

    Excuse my crude drawing, but as I mentioned above, when cutting thinner material, you want to angle your cut slightly away from your good material.

    Last edited: Nov 12, 2011
  15. rcoffey
    Joined: Dec 13, 2007
    Posts: 161


    do not set the acetylene at 15!!!!!the gas is un stable at 15 and can spontanious combust. 5 to 7lbs will cut up to 1/2 inch if all is clean.that is why the regulator red lines at 15 lbs!
  16. ^Yup, that's pretty dead on. Acetylene shouldn't be set anywhere near that high.

    Here's a correct tip chart size. Use it. Many cutting problems can be solved by using the correct tip, and pressure settings. Thanks to my college instructor, I'm one of those guys that can make those "plasma looking" cuts using a torch. Much of it is practice, and a steady hand (or a good guide), but, few people realize the importance of correct adjustment of the equipment.

    Everyone's correct that you're putting too much heat into the work piece, and that is causing the molten metal to flow back in, but, the last thing in the world that will fix that is an increase in acetylene pressure. You need to decrease the heat being put into the workpiece. Since you aren't a machine, I'd recommend decreasing the acetylene pressure, and oxy accordingly to match the travel speed you're comfortable with. If you can increase your travel speed that's great, but, few can really haul butt without a pool cue (cutters torch).

    You don't need anywhere near 10psi of acetylene. As you can see from the chart, 10psi would cut 10" thick material. You need more like 3-5 psi, and I'd personally stay on the low end of that for the material pictured. On the 3/8" I'd jump up to 4 or 5 psi. Just remember, with a torch most people tend to think more is better. It doesn't need to be a roaring flame to get the job done. Try backing the acetylene down to a slightly sootier cloud on startup then dialing in the oxygen until it roars, then back it off just a touch until the cones start to distort. A nice quiet preheat flame, with only a slightly louder cut flame works good on thinner material. It doesn't need to sound like a jet engine to cut well.

    And go get yourself some good quality new tips. $12 well spent.
    Last edited: Nov 12, 2011
  17. Mindover
    Joined: Jan 18, 2009
    Posts: 1,625

    from England

    Once you have established that you have the correct nozzle size and are using the correct pressure. (I cant help with this because I am from the UK and nozzle sizes are different here)

    The correct way to set your flame is very simple.

    you should first set a neutral flame without the trigger pulled - When you pull the trigger you will have the proper flame for cutting. If you do not know how to set a neutral flame I show it for welding on my youtube footage (same procedure) Here is the link

    Last edited: Nov 12, 2011
  18. tommy
    Joined: Mar 3, 2001
    Posts: 14,757

    Member Emeritus

    Start with the basics. Get a new correctly sized tip for the thickness that you are cutting. put it on set the pressures and light it up. Now look at the flame and listen to the sound that is made when the lever is pushed. You should be able to see a dark line all the way through the center of flame...the oxygen. Listen to the will have a slight "cackle" to it. That is the sound and look of a clean cutting tip. It will get dirty and the line will go out the side of the flame and it won't sound the same....the tip needs cleaning. Think of it as a rifle bore. If you use the correct sized tip cleaner to remove the dirt and not change the size of the bore, it will last a whole lot longer. I worked with welders that would not let an apprentice use their tip. They protected it like it was gold.

    Most people wait way too long before cleaning the tip. look for that line in the flame extending a couple of inches away from the tip.

    The oxygen from the center hole increases the temp of the metal above the molten state so only that point is molten and not the metal on either side of the oxygen stream leaving a sharp edge. It's a lot easier on heavier metal than 1/8 or 3/16 boxing plate but practice makes perfect. Keep increasing your speed until it won't keep cutting.

    Going too slow is causing your problem. Once you understand a clean tip and the speed it will be like night and day. Like any skill it's a feel that is learned. If you move too fast it stops cutting, too slow and it welds itself back together.

    When you get the hang of it, the part will fall out and any remaining slag will fall off of the part when it hits the concrete. It will need very little slag removal or grinding. If there is a roll of slag remaining on the part, the tip is probably dirty. Instead of the oxygen passing through the metal at a 90 degree angle the metal is rolled up on the side of the piece.

    The metal will not be molten when you start to cut...the oxygen raises the temp so that the surrounding metal never gets hot enough to melt...only the path of the oxygen giving a nice clean edge on either side.

    It's easier to cut a thick piece with a tip that is too small by moving slowly than it is to cut a thin piece with a tip that is too big. You can't move fast enough.

    Get a good tip and tip cleaners. Try to go as fast as you can.

    I bet your tip is way to big. It's like trying to do an oil painting with with a house painters brush. The both apply paint. I think I used a 00 tip but talk with the welding supply store folks.

    Did I mention keeping it clean?:D I always had my own tip cleaners and never let anyone use them. Mine were never bent or broken.
  19. Well said! I would use a 0 or 00 tip,keep it CLEAN!!! practice,practice practice! You should be able to cut 1/4-3/8 steel and leave NO SLAG with enough practice! When I went thru apprenticeship for the Ironworkers,we did not move on to anything else until we could cut with NO SLAG! jmho Redliner Union Ironworker 32 years...
  20. Well said! I would use a 0 or 00 tip.Keep it clean,practice, practice, practice.You should be be able to cut with NO SLAG! When I went thru the Ironworkers apprenticeship,we were not allowed by our instructor to start learning how to weld until we could cut SLAG FREE! jmho Redliner Union Ironworker 32 years
  21. 51custom
    Joined: Feb 15, 2011
    Posts: 102


    At a Linde safety seminar several years ago our shop rep. suggested to never set your acetylene torch pressure more than 7 PSI for extra heavy material...3-4 PSI for reg. cutting jobs. This was in a large off road mining truck facility...
  22. lolife
    Joined: May 23, 2006
    Posts: 1,125


    Kind of dumb reply, but setting up a cutting torch is not always obvious. The lower oxygen valve on the torch is opened all the way, and the forward oxygen valve on the torch is used for setting the neutral flame.

    Turn off the forward oxygen valve, and crack open the acetylene valve about 1/4 turn, light the torch, and set the normal bushy flame without soot. Then crack open the forward oxygen valve and adjust to a neutral flame..
  23. Deuce Daddy Don
    Joined: Apr 27, 2008
    Posts: 5,262

    Deuce Daddy Don

    I concur!---As an old retired pipe welder, most of you have the correct answers.
    For that thickness metal use a 00 cutting tip & make sure ALL HOLES are free & clean.---5-10 acet.---30-35 oxy--oxy valve on torch butt wide open---neutral flame on acet.----adjust oxy on side valve to sharp points----press cutting attachment handle down all the way & continue to adjust flame points to a sharper point(s).
    For just making straight cuts I suggest using a THICK (3/8) pc. of angle iron 1-1/2 or 2" about 12 or 16" long & use a C clamp or vise grip type pliers.
    Set the angle iron at desired distance from your soapstone line by holding torch tip against angle iron & tip of flame 3/8 from metal edge, start cut by pressing down lever when metal is preheated enough to be red in color.
    The speed of travel will be determined by the nice clean cut behind the flame, if you are getting "Turkey gobblers", increase the travel speed just a LITTLE BIT, going too fast will cause the cutting process to cease & sometimes tip will "POP"---Then you have to start over!!
    Hope this will help you!----Remember, practice on lots of scrap pcs. will make you better at your job!!------Don:D:D
  24. super plus
    Joined: Dec 14, 2006
    Posts: 566

    super plus

    WOW ! Watch you don't burn you shop, garage, house or neighbourhood down!
  25. Engine man
    Joined: Jan 30, 2011
    Posts: 3,480

    Engine man
    from Wisconsin

    You must have a different tip numbering system. In the US, a number 8 tip would be used to cut about 12 inch thick steel.

    I'd use a 0 or 1 tip on sheet metal. 7lbs acetylene and 20 lbs oxygen. The instruction manual for your torch should have some instructions. It's a combination of the correct tip, correct pressures, properly adjusted flame, proper pre-heat, proper distance and proper cutting speed.

    You are actually burning the metal to cut it and only the metal directly contacted by the oxygen will burn.. If it melts back together, you are getting it too hot. You need to move quickly on sheet metal.
  26. When everything else is right, push the oxygen lever all the way down when cutting.
  27. chigger
    Joined: Jan 30, 2009
    Posts: 169


    I you can't get it, give me a shout. I'm just south of Kc and in the city everyday;
  28. tinmann
    Joined: Nov 11, 2005
    Posts: 1,588


    Holey Moley............ at 15 psi, Acetylene begins to become unstable...... at 28 psi it will spontaneously explode. These figures are at normal room temperature. Acetylene is nothing you want to mess with. The highest pressure I've ever used Acetylene at is 7 psi. For cutting, Oxygen can be cranked up to 30 psi (or even 40 if you're cutting heavy stuff). Like others have said, I'd be curious to see the quality (sharpness) of your flame.
  29. 5 and 15 works for me every time yo.
  30. niceguyede
    Joined: Jan 19, 2009
    Posts: 633

    from dallas


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