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Acetylene Cutting


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#1 tab112983

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Posted 28 March 2012 - 10:33 PM

Hello, I am learning how to cut with an acetylene torch. I have watched a lot of videos of people making nice precise cuts and every time I go cut I burn a wide swath through. I read an article that said you are supposed to put the thickness of the inner flame a little more than the thickness you are trying to cut. I am trying to cut 1/8th inch D2 steel and I cant seem to get my inner flame to that size without turning it into a bunch of little individual blue flames. My torch isn't a victor its some knock off. Do I need to pony up and buy a better torch or am I don't something wrong?




#2 Rich Hale

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Posted 28 March 2012 - 11:24 PM

You are trying to cut a steel that is really close to being a stainless, and stainless does not cut at all with a O/A. A side grinder with a cut off wheel and full protection will do it,,and if it is annealed,,meaning if you can file it,,can be cut with a good hack saw blade. And if you are trying to make a knife you most likely do not have the right stuff in a home shop to heat treat it..Google heat treat for that steel if you like. The area around where you heated it up will be really hard,,,

#3 Toymkr

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Posted 29 March 2012 - 01:29 AM

The key to OA cutting is selection of a proper tip size for the material being cut, a clean tip and fuel & oxygen pressures set correctly. Tip cleaners are essential as well as NOT using the torch to hammer off an incomplete cut. That distorts the gas ports and xxxx near ruins the tip. The only salvation for a hammered tip is filing it back and hopefully restoring smooth bores. If that doesn't work, make a necklace charm out of the copper for your girlfriend because it is useless to try to cut with it. It sounds like you are either using too large a tip or you are cranking up the pre-heat too high and basically melting rather than cutting. The preheat flame only needs to start the metal melting and the oxygen jet from the center does the cutting once the metal starts to oxidize...a steady hand helps too. <grin> Do a search for 'cutting torch tips' and check out various torch manufacturer's websites where they'll list metal thicknesses for each size of tip. A search for 'cutting torch video' will also get some good pointers.

Rusty steel is a bear to cut and I highly recommend grinding both sides to remove any scale before you try a cut. For cutting diamond floor plate, cut from the smooth side and angle the torch so that the flame leads. That preheats the diamonds ahead of the cut and you'll cut smoothly.

I learned torch cutting from some highly regarded old pros in a shipyard and practice over the years has taught me a lot...and I'm a pretty fair 'burner' if I do say so. <grin>

#4 jmccustomknives

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Posted 29 March 2012 - 05:55 AM

1st rule of the cutting torch, if it doesn't rust it won't cut. D-2 has way to much chromium not to mention it is an air hardening steel which means you'll have to deal with the heat affected zone. Even 52100 can be difficult to cut, it doesn't have near the chromium that D-2 has. Better to use a side grinder and a slicer wheel, they are the best thing since sliced bread. If your having trouble cutting with the torch contact your local welding supply, most of the time they can help. I do however have customers who travel and they tell me stories of other suppliers that didn't have a clue. First thing, get a tip for the thickness you are cutting. Second, set the pressure properly. Be steady, don't catch yourself on fire.

#5 pkrankow

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Posted 29 March 2012 - 08:33 AM

Believe it or not once you get preheat you can turn the acetylene off and just use the oxygen to cut, as long as you do not loose your preheat.

If you are making a long cut you may want to fab up a simple guide. I have used wood on thin material... but it does char and sometimes catch fire. Thinner than 1/4 inch mild steel pre-heats very quickly, so wet/damp 1x wood survives. I never tried wood as a guide on anything thicker, and I don't currently have my own O/A kit.

Here is what someone who does this professionally did for a guide.
http://www.iforgeiro...eel-boring-r356

No reason to not do this in a line or other shape.

Torch cutting tool steel was well summed up already. I don't recommend it either.

Phil
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#6 ThomasPowers

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Posted 29 March 2012 - 09:38 AM

If you are trying to cut a profile on D2, get it annealed from the factory and then use a vertical band saw! My first job apprenticed to a swordmaker was cutting 36" lengths of D2 on a bandsaw...

(You can always send out your D2 blade to be heat treated by someone with the computerized ramping controller heat treat oven)
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#7 tab112983

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Posted 29 March 2012 - 11:26 AM

Thank you all for the help, your advice is invaluable. I will use my angle grinder to do the job until I can save up for something that cuts a little more precisely. Do you think a plasma cutter is worth the cash?

#8 ThomasPowers

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Posted 29 March 2012 - 11:41 AM

Yes, No, Maybe depending on your situation!
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#9 Spears

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Posted 29 March 2012 - 12:15 PM

Thank you all for the help, your advice is invaluable. I will use my angle grinder to do the job until I can save up for something that cuts a little more precisely. Do you think a plasma cutter is worth the cash?


I was lucky to have purchased both Oxy/Ace and Plasma ~13 years ago before things became less affordable. Its hard to beat the portable nature of the Oxy/Ace setup as far as not needing electricity and compressed air like with Plasma. But if you cut an abundance of sheet metal or plate up to 1/2" thick, you can hardly beat the "ease of use" with Plasma.

I hardly ever use my Oxy/Ace for cutting unless I have to blow the U-joint out of an axle in which I can't get the plasma tip down in there between the lugs and around the curved shape.

I find it vey bothersom and expensive to have to get tanks refilled.

To get a "good cut" with the Oxy torch, it takes a steady hand and I also have to pay attention, concentrate some, and try at it. With comparison, I would have to call Plasma "effortless". Is it worth the cash? Well, everything is, as long as you have some. Good luck with your cutting. Spears.

#10 SmoothBore

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Posted 29 March 2012 - 12:31 PM

Having established that flame cutting Tool Steel is a difficult, unrewarding proposition, ... I'll just offer some basic info.

Proper Gas Pressure settings, seems to be the most common problem for beginners.

#1 - Gas Pressure, ... To properly adjust the Gas Pressure, turn on the Acetylene, ... light the Torch, ... and then add enough Oxygen to the flame, so that it stops giving off a sooty smoke.

( Now that you have Gas flowing thru both Regulators, the adjustments that you are about to make, will remain constant when cutting. )

The Acetylene Regulator should now be adjusted in the range of 4 to 6 PSI. ( Turning up the Gas will NOT increase the heat, and will overwhelm the mixing capacity of the Tip. )

Now set the Oxygen pressure at 20 to 24 PSI. ( Once again, more pressure WILL NOT improve the performance of the Torch, ... and will make it increasingly difficult to maintain a proper flame. )

Having adjusted the Regulators, we can now adjust the Torch Flame.

#2 - A Cutting Tip has several "Jets" that allow it to do 2 jobs, at once.

There is a Center Jet, controlled by the "Trigger" or "Lever" on the Cutting Head, that directs the stream of Oxygen onto the pre-heated steel. ( There is a knob on the Cutting Head, that turns the Oxygen on and off, ... obviously, it needs to be turned on. )

The size of the Tip will determine the size of the Flame, ... but regardless of the size, you want to adjust the Gas mixture, so that the ring of Pre-Heat Jets that surround the center Cutting Jet, are burning at their most efficient setting.

The 2 knobs on the Torch Body control the Pre-Heat Flame.

Turn the Acetylene knob all the way on when you light the Torch. ( The Acetylene Regulator and the Tip size will control that part of the process. )

Now, as you dial open the Oxygen knob, the bright blue flame from the Pre-Heat Jets will become shorter, brighter, and increasingly more defined, ... until they reach a point where they are very distinct, individual "needles" of flame, shrouded in a sheath of pale blue flame, of about the same diameter as the Torch Tip.

This is a properly adjusted "Cutting Flame", ... and will not blow out, when you pull the trigger on the Cutting Jet.

Now we can cut steel.

#3 - With your properly adjusted Torch is held at the point where the tips of the Pre-Heat Flame "needles" are just touching the edge of the steel at the point where you want to start your cut, ... heat the starting point until the steel begins to emit pale yellow "sparks". ( This is the carbon in the steel beginning to burn. )

As soon as the sparks start to appear, ... and holding the Torch perpendicular to the steel, ... it's time to pull the trigger.

Watch the Cutting Jet blow thru the steel, ... and move it along the cut line as steadily, and quickly as you can, while maintaining a clean cut.

Moving the Torch too slowly will cause the edges of the cut to melt, and flow back together, ( Bridge ) behind the cut.

( A certain amount of "Bridging" is inevitable, and is nothing to worry about. )

On thinner material, where the Pre-Heat process is melting too wide an area, it helps to angle the Torch so that you are, in essence, "pushing" the Cutting Jet out ahead of the Pre-Hear zone.


By experimenting with Torch angles and speed, you will quickly become confident and proficient.



.

#11 beth

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Posted 29 March 2012 - 01:41 PM

do you know, i never even knew you were meant to preheat.....! and have never done so... but have not used my oxy/ace for years to cut with, i had a plasma cutter which was FANTASTIC but it has been stolen from me :( :( it was great and sadly i cant afford to replace it... so thats why im reading the thread, to check out the details on proper o/a cutting. very informative, as usual thankyou very much :)

#12 Iron Falcon 72

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Posted 29 March 2012 - 10:08 PM

Smoothbore, that has to be the best explanation of acetylene cutting I've read. Thanks!

#13 Robert Yates

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Posted 21 April 2012 - 12:39 PM

this one shows a good cutting set up http://video.search....etylene cutting

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