Thread: Oxy Cutting (neatly)

Hi Quercus,

Too bloody easy mate!
Firstly the thing is to understand why you are having trouble with the 3 mm thickness.

It sounds as though the plate is not cutting cleanly as it does with the thicker plate sections.

The 3mm plate (in this case) requires just a certain amount of heat to raise it to ignition temperature and no more .

Grab all your cutting nozzles and have a good look at them. Sizes range from No#15 ( cuts to 75mm ) No#12 (will cut to 20 mm) No#8 ( will cut to 6mm) and No#6.

Look at the business end of each and you will see as the numerical size gets smaller so does the gas delivery holes in the face of each. As the holes became smaller less gas and therefore less heat.

No#6 is what you need for 3mm and the correct cutting pressure. To set the correct pressure set the flame up to the neutral condition. The cone tips of the preheat flames are rounded at the very tips -not pin pointed.

With that depress the cut lever and while maintaining a jet stream flame,adjust the oxygen pressure regulator until the cutting jet flame goes to its longest length. One may have to re adjust the preheat as this will slightly move the setting off neutral.

All the above assumes that the cutting nozzle is clean which will be evidenced by a long skinny jet flame ,which has its own unique sound when set correctly.
Lastly when cleaning with the nozzle cleaners.

Assume the attitude, that the tool is a bunch of skinny wires which is merely meant to dislodge and foreign bodies in the nozzle openings and you will be OK!.

Its easy to spot someone that does not understand this function.Their nozzle cleaners are bent and twisted to the *****!!!.

Gifted individuals may even manage to break off these wires inside the nozzle openings.

The rest of us who understand such things obtain a set of nozzle drills (operated with the fingers) and enjoy good cutting performance from our well maintained cutting torch and nozzle.

The rest is merely maintaining your cutting travel speed to obtain about a 15 degree volume of slag. Also keep a distance of about 1-2mm between preheat flame tips andplate surface.

With a good quality pair of gloves you will find once you learn to relax you can free hand these cuts and throw away the trainer wheels that most seem to want to stick to.Another thought too, is the cutting lever.It is either fully depressed or it is not. A throttle it is not!

Recapping, the crux of it is having just enough heat and moving at the set distance from the work using a clean nozzle.
Keep the torch perpendicular to the plate surface 90 degrees in any direction.

If its possible can you lets us now when the cuts improve for you.

Cheers

Grahame

I would not bother cutting anything under 3 mm with an oxy especially plate.
It can be done but you also have the problem of distortion to deal with.
Use a cut off saw an angle grinder or a plasma if you are lucky to have access to one.

Thanks Grahame.
When you are adjusting the oxy flow, are you saying that you do that with the pressure regulator, or the knob on the torch.?
A boilermaker once showed me that you have the handpiece oxy knob open fully, and do the fine tuning with the one on the torch /blowpipe.
When I did my welding course I was told to get a roughly neutral flame, then depress the cutting valve, and adjust the flame till all the outer cones were sharp - not so?

All the above assumes that the cutting nozzle is clean which will be evidenced by a long skinny jet flame ,which has its own unique sound when set correctly.

From my apprenticeship days " the sound of tearing brown paper" it's always worked for me!

Hi Quercus

The pressure adjustment referred to can only come about by adjusting the regulator gauge valve adjustment knob.

The oxy flow control knob (on the lower end of the torch hand piece - above the acetylene knob ) is turned fully open.

The oxygen flame adjustment control knob (when set up on the hand piece) is knob on the left hand side of the cutting head


Pin point flame indicates an oxidising flame. The preheat flame while set at that will oxidise ( burn) the area beside the kerf. If its set too oxidising ,you have to travel like a cut cat to avoid melting of the cut edges.That in turn stuffs up the slag volume & angle thingy which in turn is your visual indicator of how fast to travel.

Its just another tweak that separates the fellow that seeks to do a great job from the one the just does the job,in my humble opinion.


As I said before the flame is set for just enough heat to heat the plate to ignition point. It all hinges on :

• A clean correct sized nozzle- #6 that a hole of.6mm in this case.
  
• The pressure (at the regulator ) set to suit the nozzle. The jet flame set up properly is up to 250mm long and has a very distinctive sound.
  
• A travel speed (you control this ) at such a rate that produces the volume and angle (10 to 15 degrees) of spray.

The will leave minimal slag adhering to the underside of the cut .The cut edge will be clean and sharp and square.

try these things OUT and I will bet you will observe a vast improvement.

Cheers

Grahame