Set Up

I have been trying to set up oxyacetylene for cutting. I have a "#12 cutting tip"... but I couldn't find any data accompanying it. I wanted to cut pipe about 5mm thick. I read that "For cutting, use 15 psi for the oxygen and 2 psi for the acetylene; but these amounts can vary somewhat according to what is being cut". The gauges on the oxygen regulator show 0 to 3500psi/0 to 240 kpa (x100) And 0 to 200psi/0 to 14 (x100kpa) The gauges for acetylene show 0 to 400psi /0 to 27kpa And 0 to 15 psi/0 to 1 kpa (x100) 15psi = 103.4kpa which is a setting which is barely visible. I rang a shop and was told to use 40psi Oxygen and looking at charts for torch tip types I set 5 (or was it 10?) on the acetylene. When I lit it there was a large flame and a lot of soot it back fired and went out. The second time I pushed the trigger and got a feathery looking flame..... (and didn't know whether I was Arthur or Martha.... so I quit). I'm too late to enrol in a course for this year. John

Reply to
Loading thread data ...

Reply to

You'd want probably a 00 or 0 tip, not number 12. A number 12 tip would be handy though if you had to say scrap out a battleship's 16" armor plating.


Reply to
Grant Erwin

Hi John, The question you have asked here is at once pretty broad and pretty specific; pretty much akin to asking someone 'should i turn the gas up all the way when i want to cook some food?' Setting an oxy torch is a pretty basic skill that many people can do, but then a whole bunch of variables come in to play..... someone with some experience can sum up in 10 seconds what it might take a whole book to explain. so, with tongue only slightly in cheek, here is your worded guide to setting up an oxy;

lets start with the tip.... every company has their own numbering system and designation for tip types. In australia for example where i live, one of our biggest suppliers is CIG. A #12 tip in their range is suitable for a wide range of purposes, I would probably cut just about anything from 5mm to

20mm with this tip, though its a bit fat for 5mm and a bit thin for 20mm. a #8 or #6 would be more appropriate for 5mm steel in their range. but each company has their own system. Once you have a bit of experience you dont really need to know the number; a quick look at the size of the holes will tell you what that tip will cut. But be aware that your #12 may be designed to cut hugely thick plate depending on who manufactured it.

Is it second hand? do you have and know how to use a set of tip cleaners? If it's new, you dont need to worry... it will be easy to set. A large part of setting a tip by feel (rather than by the book) relates to the sound of it. A worn tip will never cut cleanly, and will never sound right. Buy a new one if you have to, they only cost a couple of dollars.

So lets start.... hopefully your bottles are full? empty bottles wont have enough 'drive' to keep a good flame going. Are they big bottles or small ones? can you pick them up with one hand? Then they are very small and you wont be doing much cutting with them! Are they about 3 feet high? Then you will get some good usable service from them. Are they 5 feet high? Then you needn't worry too much... you have plenty of time to set your flame correctly. Do you have a 6 or 12 pack of 5 feet high bottles on a common manifold? Then what the hell are you doing? Come to australia and I'll give you a job doing destructive cutting!

Let's start with a look at the torch... does it have a separate cutting head? Who made it? How many nobs does it have, 2, or 3? I will assume that you have 3 knobs; 2 down the bottom (oxy and acetylene) and one at the cutting head for mixing. Lets start by setting the acetylene since it's the easiest to set. Set your pressure to about 5psi on acetylene, open the valve on the torch and light the flame. how big is the flame? If its only a couple of inches, start turning the acetylene knob on the torch to be more open.... open it up all the way if you can. Thats the goal here. If it is very small then its probably very quiet, and very sooty, leaving black things floating around the air and landing on everything! Now that you turned it up all the way, what is the condition of the flame? Is it roaring loadly, or still quiet and relatively small? You will notice when you light the flame, that the flame itself is directly 'connected' to the tip ie. touching. as you turn it up, it will become less sooty, louder, and at some point the flame will separate from the tip, leaving a gap. The goal for setting an acetylene torch, is to have the flame as big as possible *without the flame separating from the tip*. Once the flame separates from the tip, that is too much acetylene. So open that acetylene valve on the torch as much as you can, now adjust the *regulator* so that the flame is only just separated from the tip. That is plenty of pressure (no matter what the gauge, or the book says). Leave it at that pressure, and then turn down the acetylene knob on the torch *just a little bit* until the flame joins back onto the tip.

Now for something a bit trickier, setting the oxygen pressure. Most people set it *way* too high. this doesnt make a bad cut, but it wastes a lot of oxygen! For oxygen, you want as little as possible, but as much as necessary. Generally, you want to err on the high side. Start at somewhere around 10-15psi. If you have 3 knobs (two on the bottom and one mixing knob at the cutting head) then close the mixing valve completely, and open the bottom valve all the way. The flame should still be acetylene only at this stage. If there is some oxy in there, then you have a leaking mixing valve. now turn the mixing valve on a bit.... do you know how to set a ballanced flame? turn the oxy on more, until you see a blue cone appear.... turn it on a bit more, and the cone will get smaller until you see 5 or 6 (depending on the number of holes in the tip) small blue cones off the tip. At some point, it wont matter how much more you turn the mixing valve, those little cones wont really get any smaller. It will get noiser though, and it will eventually blow itself out. What you are aiming for is to make the cones small, and then stop at the point where they become as small as they can get, or maybe just slightly bigger than that. You dont want to keep on adding more and more oxy.

Ok, so now here comes the tricky bit.... Youve got a ballanced flame, now press the cutting lever. What happened? Did the shape of the flame change? Did a big blue cone appear when you did it? Did it blow itself out? Then, while pressing the lever, adjust the mix until you get the same ballanced flame back again. Now you have the ballanced flame, when you release the cutting lever, does your flame become very noisy or blow out? then most likely your torch needs attention. The mixing valve at some stage when it is worn will not keep a ballanced flame during all times. You can have them rebuilt, or you can buy a new one. Most torches will give so-so results for a while before they fail.... They wont be quite ballanced at rest, or quite ballanced at cut, but you can set them somewhere slightly in the middle and still cut with them.

Now if your torch still ballanced, were you able to get a ballanced flame in both states? If you couldnt make your 'cone' small enough, then you need to turn up your oxy pressure. If you had no trouble, then its time to turn it down. If you press the cutting lever and the torch takes off like a rocket, almost pushing your hand back, then you need to turn it down a lot. If you have a good new, or freshly cleaned tip then you can tune the oxy pressure by the sound. When you press the cutting lever is it very loud? Too much pressure, turn it down! The perfect sound is a little bit quieter, and it sounds exactly like paper tearing... a kind of 'ffffffffffft' sound. If you only get a quiet 'sssssssss' sound, then you may need to turn your pressure up a bit, but most people set way high, so you can assume you need to turn down. Just hold that lever, and while you are holding it, start turning the pressure down and listen. At some point you will start to hear the sound of paper tearing. This is the right pressure. You will only get this sound with a good new or very well cleaned tip (which will also give you excellent cutting!). Now reballance your flame, because it will have changed with the new oxy pressure... when you get the flame reballanced, press the cutting lever again... it should come in with a gentle pressure, not like a rocket, and should give you that 'tearing paper' sound. You've got it right. Now start cutting. bear in mind though, that tip doesnt need to be as close to the metal as you think. Keeping it 10mm off the surface will prevent spatter entering the tip and destroying it, it will also give a cleaner cut.

While this action is hard to describe in writing, its easy to do once you have seen and heard it. A practiced person can pick up any torch/bottle/tip combination with no knowledge of that particular item, even if the bottles have no gauges on the regulators (very common in mining!) and have the pressures and flame perfectly set in 20-30 seconds. And then you can get a ballanced perfect flame in about 3 or 4 seconds every time after that. It does take a bit of understanding, so watch someone else do it if you can (who knows what they are doing!)


"JohnH" wrote in message news:46a6c36b$

Reply to
Shaun Van Poecke

First, put that #12 tip on a shelf in your trophy cabinet, or check and see if the Smithsonian is interested. I didn't know they made them that big.

For 5mm, approximately .2", you need a much smaller tip. Look at Victor for a copiable tip guide. For that, probably a 0 or 00.

Never, ever, use so much acetylene that the needle goes into the red zone.

Something that a lot of people don't understand is that the oxygen is the thing that makes it all work. Lots of thicknesses of metals have the same acetylene pressure, just increased oxygen for increased thicknesses, plus, of course, a bigger tip.

When lighting the torch, turn on the acetylene slightly, and the oxygen slightly. This will get rid of the black boogers. You'll get the hang of it shortly. Look at the little blue cones. When they don't change when you hit the cut handle, it's adjusted close to right.

Go get the guide, a tip or two, some scrap, and practice. It ain't rocket science. If you know someone who knows how to do this, they can show you in thirty minutes what it might take you a week to learn. A few cold ones, and it's a pretty good deal.


Reply to

Thanks , Sean , a very informative description !

Reply to

Shaun's post should answer many of your questions, but there's I few things I wanted to add.

First, do you know the difference between a welding torch and a cutting torch? You can't really use a welding torch for cutting, and you shouldn't use a cutting torch for welding. So if you want to cut, you have to start by getting a cutting torch and a correctly sized cutting tip. They make dedicated cutting torches, but what you will normally find is a single handle that can be used for welding or cutting. For welding, you attach a welding tip to the handle. The welding tip will have a single hole in the end. For cutting, you have to attach the cutting adapter which will have the extra knob for controlling the o2 for the pre-heat flame, and a lever to turn on the cutting O2. The cutting adapter will then have a cutting tip attached to it which is nothing like the welding tips. The cutting tips have a large hole in the center which is where the O2 for cutting comes out when you press the lever, and 2 to 8 (4 or 6 being typical) smaller holes around the center hole for the preheating flame.

Welding works simply by burning the O2 and Acetylene in a even mix to produce heat. Cutting works completely differently. You cut by actually burning the metal with the O2. Because of this, with cutting, you need a lot more O2 than you do with welding. So with welding, you might have the pressure set at 5psi for both the O2 and the Acetylene, for cutting, you need much higher pressures for the O2.

You can use a welding tip to melt a whole in the metal, but that gives you a very messy cut with molten metal dripping everywhere. The cutting torch, when set correctly, and used correctly, makes a very clean cut.

Next, Victor, which is one of the best known manufactures in the US, doesn't make a #12 cutting tip. They only make tips from 000, to #8. And the #8 is designed for cutting 12" thick steel and needs around 50 psi of O2 (a huge number). They do make a #12 welding tip, but that's the largest they make (or at least the largest I see listed on their card which gives you pressure settings).

Next, on pressure, Acetylene becomes dangerous above 15 PSI. I think that's the pressure it becomes unstable when mixed with air. Most acetylene hose-side (low pressure) gauges are marked in red above 15 PSI and you should never set the gauge into the red zone. The tank side gauge will typically be 200 to 300 psi when the tank is full.

That's a bit low, but can work for a very small tip. The smallest tip Victor makes, a 000 tip for cutting 1/8" thick steel needs 3 to 5 psi for acetylene and 20 to 25 psi for O2.

Setting the regulator pressure too low will keep it from working. Setting it too high only means you have to close the knobs on the torch a bit more to keep the gas flow at the correct speed. SO it's better to error on the high side than the low. But don't ever go over 15 PSI for the Acetylene.

A 200 PSI o2 gauge is a large gauge but not unusual. 02 should be more like 25 to 50 for cutting depending on tip size.

Like Shaun talked about, you start by turning the knobs on the torch off, and then setting the correct regulator pressure for fuel and O2. You will have to open the knobs on the torch to vent pressure to lower the pressure.

You then open the fuel knob a very slight bit (1/8 turn) and light it using a striker (don't use a match - you will burn your hand). You should get a small flame with lots of soot (depending on how much you opened the fuel knob). You then turn up the fuel knob slowly. At some point, most the soot will go away. At some point after that, you will see the flame jump away from the end of the tip. You should operate the torch somewhere between those two points. If the flame doesn't jump away from the tip even when the knob is all the way open, your pressure is set too low. If it jumps away long before you open the knob all the way, you have it set too high. But as long as you can adjust the knob to get the fuel-only flame in that range between where the soot stops and the flame separates, it will work for you.

When you turn the 02 on, it can backfire and go out if you turn it on too quickly. It's even more likely to backfire and go out if you have the Fuel turned down with a small sooty flame. If it backfires, just turn the knobs on the torch off and start over. Once the fuel make is set, open the O2 knob very slowly to keep it from backfiring and going out. Some torches are most sensitive to this than others.

Ah, if you have trigger, you are using a cutting torch so all should be good there. I guess I should have noticed your mention of a trigger before I talked about cutting vs welding above....

As Shaun talked about, you need to set the pre-heat flames to a neutral flame before you play with the trigger. If you have a typical combination cutting torch with three knobs, the knob near the trigger controls the O2 flow for the preheat flame only. The trigger controls the O2 for cutting.

Turn the O2 preheat knob off, and turn the one at the base of the torch all the way on. After getting the fuel flame burning correctly (no soot but still touching the tip) turn on the O2 preheat knob slowly. You will see 3 distinct length flames form. A short blue flame, and longer lighter blue flame, and then the rest of the flame. As you add more O2, that middle flame will become shorter. When it merges in with the shortest flame (i.e. the two shorter flames merge into one of the same length) you have the O2 set correctly for the preheat. If you turn the O2 up more after that, the blue inner cone will get slightly shorter, but you will have added to much O2. Set the O2 to the point where the two shorter cones become one. You have the fuel and O2 correctly balanced for what is called a neutral flame at this point.

Now press the trigger and see if the balance stays the same. Many times it won't. The O2 pressure for the preheat will typically drop, causing it to go back to a flame with two different inner cones. While holding the trigger down, adjust the preheat O2 knob some more to make it return to a neutral flame. It's better to have it set for a neutral flame while cutting.

To cut, start by using only the preheat flame - don't press the trigger. Heat up the metal until it turns red hot, and then press the trigger. When you press the trigger, the metal should start to burn like a fuse. Your job, is to move the torch at exactly the speed the metal is burning away. It's like trying to chase a burning fuse with torch. If you move too fast, you will overrun the cut and it will go out. You will have to let up on the trigger, pause until it heats up again, and then push the trigger to get it going again. If you move too slow, it will burn away from you and go out so you will have to restart.

Each time you restart, it makes a big mess in your cut. To make a clean cut, you have to do it in one pass without having to restart. It takes a bit of practice to keep the torch moving at just the right speed. Watch the metal burning and think of it as you following the burning metal. You don't control the speed, it burns at the speed it will burn based on the tip size you are using the thickness of the metal you are cutting. Your job is to keep the O2 flowing to the cut so it will keep burning.

It would be really really good to get someone that knows what they are doing to give you a quick 5 minute lesson. If your equipment isn't working correctly (which is quite possible if it's old), someone with experience would recognize that quickly where as someone who has never done it before won't recognize a defective regulator, or a leaky hose, or a dirty tip, etc.

There are a few things that can go really wrong - like flashbacks where the gas is burning inside your hose, or regulators exploding. And though O2 by itself won't burn, it can make just about anything else burn - like oils - or your cloths - (and metal). So it's important not to oil anything that comes in touch with the O2 (regulators or hose fittings for example) and to watch out for your O2 around anything that can burn.

Cutting is really quite simple if you don't need a clean cut (you can fix anything with a good grinder). You can teach anyone to cut in 5 minutes. Learning to make clean and straight cuts however is an art that takes practice and a steady hand with the torch set up correctly. Flame cutting when done correctly produces cuts that are generally smoother than a plasma cutter - they look like they were cut with something like a laser they are so smooth and straight - though it generally takes a machine controlled track cutter to get those results. Most cuts down by hand by people that haven't practiced a lot tend to look like crap.

Reply to
Curt Welch

Thanks for replying everyone. I'm taking the gear along to the gas company today.. and I'll show them the tip and probably get a new one. The guage on the delivery side of the O regulator is confusing as the scale seems too big (15psi on a scale 0 to

200....?) It is a second hand set ... I inherited it from my father... I know an old retired welder and he helped me set up the arc welder but, he talks fast (out the side of his mouth) and I can't follow him! I have a set of tip cleaners. I took the set to a shop and the attendant looked it over and said it looked ok and still has enough gas. The bottles are about 3 feet high. The torch is a Comet2 with a knob below the trigger. I couldn't figure out what to do with the 2 oxygen knobs. Thanks a lot for the advice, I've got a lot more to go on now. I'll print it out and have another try. John
Reply to

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.