First OA exercise is to practice moving the 'puddle' and I'm having good luck, though I'll ask a friend to check the penetration.
Now I need another piece of metal to do more practicing; I have a long length of 1/8" mild which I'd like to cut into 2"side strips for practicing.
Put on the cutting head on, adjusted the regulator and then the flame. Made a puddle then pushed the O2 lever. Did fine for the first inch, then the kerf began to close behind where I was cutting!!! Cause and cure????
Flame cutting determined by: size of preheat size of tip Oxy pressure height off work speed of travel angle of torch ( thin material)
When you re-melt the kerf you have too much heat. It may be caused by too big a tip, too much preheat, or slow travel. Cutting is done by the Oxy. The only purpose of the preheat flame is to raise the temp to kindling. Notice I am not mentioning melting temp. Randy
Now I need another piece of metal to do more practicing; I have a long length of 1/8" mild which I'd like to cut into 2"side strips for practicing.
Put on the cutting head on, adjusted the regulator and then the flame. Made a puddle then pushed the O2 lever. Did fine for the first inch, then the kerf began to close behind where I was cutting!!! Cause and cure????
"Michael Horowitz" wrote: (clip) Made a puddle then pushed the O2 lever. (clip) ^^^^^^^^^^^^^^^ There's a clue. You don't have to make a puddle. You just have to bring the metal up to red heat. Chances are if you were able to make a puddle, you were using too large a tip.
If, for some reason, you find you have too much heat, and you don't want to stop, you will have to move faster. It also helps to point the tip in the direction of travel. That helps by blowing the molten slag away from the cut, so there is less chance for it to freeze over and reclose the cut. Also, when you lay the torch over, in effect you are presenting it with thicker metal, so the overheating effect is reduced. Sometimes, for very thin metal, this is the only way you can get it to work.
The acetylene pressure won't have much effect. Not having as big a preheat flame will. So just don't turn the valve as far open. After you start cutting, you could turn the acetylene off. The oxygen is burning the steel and that produces plenty of heat.
My experience is that any twitch while cutting keeps the cut from being smooth. So I don't expect really straight lines.
No matter the gas pressures, you want a neutral preheat flame especially for thin stuff.
As Leo said, leaning your torch back will effectively increase the thickness you're cutting, making it easier to make a good cut in thin material.
You'll generally get a better cut with as small of a preheat flame as is practical. As Randy said, too much preheat will melt each side of the kerf. The only thing that should melt is the steel that's removed..
Sometimes on thin stuff you can get a little better performance by running a smaller oxydizing flame- it'll be very hot but the heat will be narrower than with a neutral flame putting out the same BTUs.
Push the cut as fast as you can maintain it and try different angles on the head. I'd lay the head at about a 30 degree angle to the steel on
1/8" stock and run just as fast as I could. Smoothness of travel is important, the smoother you are the faster you can run.
Practice following a line while you're doing this- grind a very sharp end on your soapstone, make a straight line and keep the edge of the kerf at the line, close enough that if you see more than the line you're too far away, and if you get into the line you're too close. You'll be impressed at how well you can do this after you practice a little.
Grind your soapstone with a very narrow piece sticking out the end (I'll make mine about 3/4" long and as narrow as it'll support), keep scuffing the side of the end so it's sharp.. the finer of a line you work with, the finer work you can do.
"Michael Horowitz" wrote: (clip) Since I have only one cutting tip, would trying a mix of 1# of acetylene to #10 of oxygen give a cooler flame? (clip) ^^^^^^^^^^^^^^^ This is precisely the kind of situation I had in mind when I have suggestions on what to do if you find yourself with too much heat. But don't try to do it by screwing up your oxygen/acetylene balance. Light the torch. Set up a neutral flame. Open the oxygen valve, and that will unbalance the flame, so rebalance it with the oxygen flowing. Since you are using too large a tip, you should start the cut as early as you can, so you don't overheat the steel. If it starts to get too hot and melty, stop and let it cool, and then restart.
One trick to being able to start the cut earlier is to drill a small hole, and start cutting as soon as the edge of the hole gets red. This also helps when you don't have enough heat--once you get the oxygen to start burning the steel, you really don't depend on the preheat, as dcaster and R Zimmerman pointed out.
Another read of the chapter sez "the proper way to add oxy. to cherry-red metal is to press very slowly on the ... lever until the metal is.. . This is actually a very soft, subtle touch... . ...you will learn that only a bit of oxy. is needed..." (Geary, p.209)
Well, I've been waiting for the metal to get molten, then pressing the lever all the way down. I'll try it with a bit more subtlity if Katrina will let me tonite. - Mike
Anyway, the whole thing about oxy-acet. cutting of steel is due to a unique (?) physical property of iron compared to other engineering materials - its oxide melts at a lower melting point than the metal. So when oxy-acet. *welding* you see the metal surface "sweat" before the weld pools forms because this is the oxide melting. The oxide wouldn't flow away and make the cutting process possible without this physical property of iron (and steel).
But yes, gently squeeze the oxygen valve to get the cut under way at a lower temperature. Once the cut has "caught" then you can squeeze the oxygen lever to the stop and romp along the cut, with the cut being sustained by the "burning" (literally) of the iron in oxygen.
Right, you want to start slowly as a sudden big burst of oxygen will cool the metal, but a little oxygen combines with the steel and produces more heat.
Here's an update: I went to the Robert's Oxygen shop and asked if this unlabeled tip would be considered large, medium or small. His opinion = it's a small tip. So I came home and gave it another try. Acetylene at 2-3 psi and O2 at
10-15. Gently with the lever; kerf still fills in. Try a very steep angle i.e. almost horizontal; still a problem. As another attempt to cool things down, I turn down the acetylene, then readjust for a neutral flame. no luck. adjust downward even more. no luck.
When you are cutting 1/8th material your torch should be angled and you should travel about two inches per second. Go as fast as you can until you lose your cut then slow down just a little bit. I use 3-5 acetylene and 20 oxy. I was cutting 1/8 by 1 inch flat bars on some grating last week. By the time I depressed the trigger fully the one inch was cut and it was time to release. If you are cutting correctly someone watching from a distance will see a steady shower of sparks dropping off below the material. The lever gently thing is for flame gouging. When you have the edge of your plate to red move your torch off the edge 1/8th press the trigger fully and charge into the material. If you press the trigger while pointing at your red area the material will spit back at you. I am finding it very frustrating that you can't get a successful cut. I am sure you would be doing some good clean cuts in five minutes of coaching in person. I can't even pull at my hair in frustration.... it's already gone :'))) Randy
10-15. Gently with the lever; kerf still fills in. Try a very steep angle i.e. almost horizontal; still a problem. As another attempt to cool things down, I turn down the acetylene, then readjust for a neutral flame. no luck. adjust downward even more. no luck.
Are you SURE you are running oxygen and not something else?
Last I did this was with a cheap Craftsman torch and it all worked fine. Heat the metal to red or a little better and then fire the O2 and it cuts like butter. Never even worried about how fast to turn on the O2. Something is way wrong in your setup and my best guess is that you are not really using oxygen.
Is it a mystery torch too? If not, buy the smallest tip that the torch manufacturer makes for that tip.
This is a good time to put in a plug for quality cutting torches and regulators. I was a shipfitter for 13 years once upon a time, and used a cutting torch every day. I wasn't super-good with a torch like the guys who did nothing but burning all day long every day, but I was much better than an average joe. When I left the shipyards I continued to work on metal at home (still do, obviously) but at first I simply couldn't cut steel very well. I replaced my Oxyweld regulators with a good 2-stage set made by Marquette and without changing anything else suddenly my cuts became much straighter, smoother, with *much* less slag. I put torches, tips and regulators in the category of tools e.g. taps and dies where it doesn't pay to buy cheap ones. Buy the best.
In my experience, the settings on a cutting torch aren't critical or particularly touchy. On thin material you can set the torch to about anything within reason as long as you move fast enough and severely angle the torch.
If you haven't moved the so fast that you lost the cut, you haven't moved fast enough yet.
Be sure you have an acetylene tip if that's what you're burning. It should have no more than six preheat orifices, if it's got a ring of triangular orifices it's an LP tip and it's going to be way too hot.
Too much oxygen pressure will cause exactly what you're experiencing.. as will a dirty or bunged-up tip. Do you have a tip cleaning tool? If not, get one.. but not the little set of drills, get the one with wires with little teeth on them.
Use the cleaner that fits the orifice best, and use it with care. You need to dress the edges of the orifice, but don't do it by bending the cleaner- arch the cleaner gently once it's in the orifice and use the convex side to do the work. A proper tip will sound very much like tearing paper when the torch is lit and you hit the cutting oxygen.
If the orifices in the tip are flared from abuse, you can file the tip back. Use a fine double-cut file with soapstone worked into it, file it perfectly square to the cutting orifice and use the cleaner to remove the burr in the orifices, then touch it up with the little flat tool in the cleaner set to get the burr that the cleaner brought up from the orifice.
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