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
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.
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!)
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.
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
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,
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.
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
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.