View Full Version : Oxy Cutting

09-11-2005, 11:37 PM
I've never had the advantage of formal training in welding or oxy acetylene welding or cutting. I've bodged through well enough for my own ends but I'm not satisfied with my results. I want to improve my cutting. What the problem seems to be is the cutting doesn't proceed evenly. I'm not sure if this is because of the paint or the rust on the surface or some other maladjustment. Also my kerf keeps closing on me and so I have to re-cut and melt through a lot of slag. I'm cutting 1/4" steel. I'm not sure which tip I'm using but the kerf is between a 1/16th" and less than an 1/8th" Also I'm not sure of the pressures or proper adjustment.

Any tips or advice will be greatly appreciated.



09-11-2005, 11:59 PM
I'm no "ex-spurt" but it sounds like your oxygen pressure is too low. I run the pressure at about 60psi for cutting (more for thick stuff). You are using a cutting torch, aren't you?

The smallest tip should cut 1/4" like butter. Until you get the hang of following a line, you might try using a guide. O/A cutting isn't as smooth as plasma cutting or a saw but it should dress up with a little grinding.

09-12-2005, 12:13 AM
i usually run everything really high 10 - 15 psi of acetilene or 1/7 the total pressure in the bottle and oxygen at around 80 psi or more depending on the thickness of the steel. I end up cutting 1" plate and up some days. tip size is very important as well as how clean the tip is .

09-12-2005, 12:26 AM
Clamp a piece of angle iron to the work and use it as a guide as Ken said. Concentrate on moving the torch as evenly as possible just below the speed where the cut flames out. Also pay attention to holding it vertical.

When you have the cut started the flame of the torch basically does nothing. It's the oxygen reacting with the steel and burning it that supplies the heat. You need enough oxygen to continue the reaction and blow out the slag. The amount of pressure depends on your tip and the kit as well as the thickness of the work. 60 psi is way too high for 1/4" material, 20 to 30 psig should do.

This is a freehand cut in 1/4" plate using my elbow as a pivot point.


With practice you can get a remakably clean cut.

This is a closeup of the cut edge. No cleanup has been done.


09-12-2005, 01:34 AM
Evan has it right. (BTW Evan, not a bad cut.) When cutting 1/4 mild steel you should be using a tip size of 00 with the oxygen pressure set to 20 - 25 psi and the acetylene set to 3 to 5 psi. You should be able to travel 20 to 28 IPM (inches per minute) and the kerf width should be about .05". Moving to slow will allow the cut to fuse shut.

Before starting the cut the preheat flames should be set to a neutral flame. A slight re-adjustment of the preheat will probably be needed when the oxygen lever is depressed. In most cases you want a neutral flame. Keep the preheat flames about 1/8" off the metal to be cut during preheat and the cut.

Preheat the top corner of the plate to cherry red at an angle, rotate the torch upright, and slowly open the oxygen lever.

As the cut starts rotate the tip slightly backward, without moving the torch, then back upright.

Once the cut is started, rotate the tip to point slightly in the direction of the cut and maintain a slight leading angle toward the direction of the cut. Move as fast as good cutting action (steady even stream of sparks out the bottom of cut) will allow.

When nearing the end of the cut, slow down and let the cut sever the bottom edge and continue the steady forward motion until the cut severs the top of the plate.

1/4" cuts pretty fast and most people seem to go to slow and use a trailing angle which interups the cut and overheats the surrounding metal fusing it together.

The three most useful tip sizes are 000 for 1/8", 00 for 1/4", 0 for 3/8 - 1/2".

Knock off excess heavy rust, dirt and paint along the cut line, the cut will be better.

Use soapstone to draw the cutline so you have something to follow and use both hands with one supporting the front of the torch at proper height and the other for control.

Also, relax and don't grip the torch to tight, it makes the torch easier to control.

Hope this helps some.

Phil D

09-12-2005, 01:36 AM
Try with a brand new nozzle, if you haven't already done so.


Jim Hubbell
09-12-2005, 02:34 AM
As Evan and PhilD said. I would add that a clean oxy orfice is of prime importance. Use a tip cleaner regularly. Best not a drill. To check if it is clean do the following. When the torch is fired up and ready to cut, depress the cutting lever a small amount and the oxy should show up as a long straight line. Not flare out sideways. With practice it is possible to make a cut as pretty as Evan's.

Your Old Dog
09-12-2005, 06:00 AM
I'd give PhilD's advice consideration. I had the best luck by getting a booklet and following the recomendations on tip size. If the tip is too large you melt the metal more than burn it. If you have the correct tip and it still joins behind the cut then you are going to slow. Suggest you go fast enough to loose the cut, re-establish the cut and then slow down a tad and you'll be at the right speed.

I also lined up the orfice holes so that they were are inline with the cut. (recommended by my welding book) If everything else is correct you'll get textbook cuts with proper drag angles showing in the cut. It will damn near look like it was done by a saw with clean crisp corners.

I will admint to having better luck with cutting 3/8 and thicker material. I thought 1/8 and 1/4 seperated the men from the boys if you want a really nice cut and not something that looks like it was melted thru and not cut with flame.

09-12-2005, 07:14 AM
Don't bump up the acetylene pressure to 10 to 15 psi as someone recommended. Acetylene at 15 psi or above becomes dangerously unstable. It's not the acetylene that does the cutting, it's the oxygen. The acetylene/oxygen mixture brings steel up to the kindling point then the oxygen does the cutting. Once steel hits the kindling point you don't even need acetylene, the oxygen is enough to cut but it's pretty tricky.

Follow the directions that came with your cutting torch for setting pressures.

It's very easy to cut steel but it takes practice to cut it well leaving a nice edge.

09-12-2005, 09:15 AM
Back during WW II there were two brothers working at the Brooklyn Navy Yard.

One was a cutting torch man, who was good enough he complained that the engineers failed to specify which side of the cut they wanted the slag on.

In the heat of the production race, the other, a steam fitter kept getting so beat up by carrying his pipe tools from deck to deck that he took some lessons from his brother and bought a slim triangle file at Woolworth's, and carefully set up a three cornered oxy blow hole in a cutting tip and threaded his pipes with it.

On a serious note,
If you clamp a guide bar or angle to guide the torch use some washers or cut off corners to support the guide about 1/8 - 1/4 inch above the plate and it doesn't get so blankety hot. Torch flow pattern also works better.
Most important to keep flow passages smooth and clean so the flow doesn't deflect at crazy angles. (makes it harder to thread pipe when it gets cruddy that way)

G'day Ag

09-12-2005, 10:32 AM
alot of rookies suck at torching because they dont "TURN THE DAMN TORCH UP"

when you think you have the torch set... turn it up some more! (at the torch body)

I also set the gauges like JS does 10 psi act. 60-80 psi at the O2.

1/4" should cut fast and clean ,if it is not you are screwing up and need to "TURN THE DAMN TORCH UP"

09-12-2005, 08:57 PM
Not to get into a pizzing contest, BUT...Use a 000 or 00 tip, keep it clean, O2 at 20 to 30 lbs DEPENDING ON THE LENGTH OF YOUR HOSE, longer hose more pressure, Acet around 5 again depending on the hose length.

Adjust the acet to just a feather at the flame end and no smoke, adjust the O2 to get the clear steam in the middle of the flame and a whirring sound when you squeeze the cutter handle.

TOO MUCH O2 WILL COOL THE CUT AND MAKE IT UGLY AND LOTS OF HARD SLAG ON THE BOTTOM. This is the hardest thing to get people to understand. The other thing is to clean off the rust on both sides. You don't cut with heat, you cut with O2 or more accurately you oxidize away the steel very rapidly. Use a guide and practice.

I was a "burner" at one time, had handles with tips from 000 to 6 plus curved and buttons to scarf and get in under things, so all I had to do was grab what was required to cut whatever thickness of steel at hand.

I used the 00 tip the most because I could cut from 0 to 2" steel without changing handles and only increasing acey to 7 or so and the O2 to 35 - 40. I set the tip holes to have the top and bottom hole run parallel with the cut that way I have the heat warming the metal as I progress. Don't stop. Keep the cut going. Look down into the cut and keep the molten metal flowing directly downward not trailing back or running forward, all that does is make the kerf fatter. A dirty tip will flare out the O2 and make a wider kerf also. Get a pair of light weight leather gloves, you can't cut worth s*** with your hands in the "normal" sizes welding gloves. I used pig skin gloves most of the time and held the hot stick about like I would squeeze a titty if I wanted to continue the rest of the way. The object is to keep the heat to a minimum and directed into the cut not your hands. I learned from an old ironhead when he got tired of watching me garbage up a few pieces and think they were so great.

Practice, practice, practice

09-12-2005, 09:22 PM
Right on the money, GWP!

All the acetylene you need is to initially get a spot of steel glowing red. The oxygen does all the work.

09-12-2005, 10:09 PM
A simple hint I would like to add is use a peice of pipe or shaft about 3/4 - 1" od as a guide if the cut is not too long.

Place one end near were you want to cut still holding the other end put your torch up against it start the pre heat you can roll the bar/pipe to align the cut.

This is good for short cuts doesn't heat up like angle iron and can be easily adjusted if your straying off line.

No fussing with clamps make sure it is plenty longer than the cut so you can hold on to it.

Keep using the same end as a handle and mark it hot after use so it doesn't get picked up.


[This message has been edited by zl1byz (edited 09-12-2005).]

09-12-2005, 10:41 PM
Thanks for all the input. I'm sure to get better results next time. I'll re-read this right before I cut the steel.

09-12-2005, 11:59 PM

Pipe is a good idea for a guide. I'll have to try that. I like the angle because if you have the right size you can hold the torch over the top and rest the torch lightly on it and it maintains the spacing as well as guiding it.

The problem with cranking up the O2 pressure too much is the O2 stream is no longer laminar flow. It creates turbulence in the flow which messes up the cut. Just like squirting water out of a garden hose, at a medium pressure it comes out in a nice smooth stream. Turn it up too much and you get a blast instead.

09-13-2005, 12:57 AM

As I encounter problems I envision solutions. I know that you do to. Follow along my oxy cutting solution and give me your critique.
A line must be cut in a piece of steel. The steel is coated with earthen clay on both sides. A narrow line in the clay is cleared where the cut is to be made. A narrow line is also cut in the clay on the underside precisely along the kerf.

The use of clay should help in channelling the oxygen and in focusing the preheat along the cut. On the underside the clay helps channel the oxygen and prevents the slag from attaching to the backside of the sheet stock. I think it would help in preventing overcutting. It is only a consept but I think it would help.
Any thoughts?

Call it the Jorgensen oxy-cutting masking method. JOCMASK.

09-13-2005, 07:20 AM
Steel that is cleaned cuts the best. Make sure the preheat holes are lined up so one is pointed right at the marked line.
If using acetalyne make sure to be consistant with the tip height above the steel...about 3/16" off with my torch. If the top edge is getting rounded off, you are too close.
1/4" with 00 @ 5/25 should cut well with the torch straight up. With 10 guage or other light material I angle the torch so the flame is about 20deg pointing IN to the cut.
If you use a steel guide, make sure it has no paint or spatter on it. Rub the side of the guide with a soapstone until it has a good coating of powder on it. The torch will glide smooth as silk. I even do this to my welding glove if I need a nice smooth cut.

09-13-2005, 10:20 AM
No clay. It will insulate the steel causing it to overheat. That will give a poor cut. As Russ said, clean is best. If I use a guide I give it a swipe with a sander first.

As far as the "preheat along the cut", that doesn't matter at all. When it is cutting all the heat that matters comes from the oxygen burning the steel.

[This message has been edited by Evan (edited 09-13-2005).]

Your Old Dog
09-13-2005, 10:29 AM
BTW, a professional weldor critiqued me and said I wasn't lighting up the torch with enough gas. Now I lite up the acet and open the valve till the flames leaves the tip by just maybe 3/16 or a little more, then when you open up the oxygen you'll notice that the flame makes more turbulent noise and it works better for cutting. I still use the settings as reccommended in the manual that came with the outfit, I just give it more gas on the torchhead valve. I normally work with 1/8 to 1/2" material.

09-14-2005, 08:46 AM
Just as a reminder, I don't think Spence mentioned which brand of torch he's using. Some people here have mentioned tip sizes but that doesn't mean much since tip sizes are not standardized.

When mentioning tip size you should mention the manufacturer.

Anyone know of a cross reference to roughly equate tip sizes across manufacturers? It would be handy in this type of discussion.