View Full Version : acetylene cutting question

08-24-2006, 12:15 AM
I need to cut a hole in a 1/4" plate, and wanted to use my gas rig.

I have mispalced the manual, and don't use the rig very often, so I forgot
where to set the regulator pressures. I have one of those small $139 Lincoln rigs. Can someone tell me the pressure settings please. I Googled it, but only came up with sites wanting to sell the book.


Mike W
08-24-2006, 12:39 AM
You should find this chart helpful: http://www.hoopersupply.com/tipchart.html

08-24-2006, 12:50 AM
I've never used one of those cutting outfits but have used hundreds of others.
For anything like that the 5 and 25 rule will always serve you well.
And yes...with the proper tip you can still cut some pretty thick steel with those settings. The lower pressures work well for thin stuff like 1/4" etc as well.

08-24-2006, 01:27 AM
Before I got a couple of "big" torches, I used one of the small Craftsman Oxy/Map torches connected to Oxy/Ac. I cut 3/4" plate on an angle with it. Still have the bearing press plates I made. Still use the torch too. It can be done. For 1/4", the 5/25 should work. Heat to red then hit the cutting valve. It should cut like butter.

On second thought, you may have to juice the Oxy a little higher--Maybe 40.

Your Old Dog
08-24-2006, 08:38 AM
If you don't have much experiance "pierceing" steel then be carefull. If working on a table top surface you know that the tip faces straight in until it gets molten and then you move the angle to about 8 degrees away from you so you don't bath yourself in molten metal?

being a rookie I find 1/4 more difficult to cut then 1/2 because you have to move so much quicker and I can't get a smooth cut.

08-24-2006, 08:52 AM
being a rookie I find 1/4 more difficult to cut then 1/2 because you have to move so much quicker and I can't get a smooth cut.

YOD...that's likely because you have the wrong tip size OR too much O2 pressure. A lot of people think you need high O2 pressures when in fact it hurts more than it helps when cutting thin stuff.
Ken very well could be right about this with the small torch...I don't know, I've only ever used the bigger outfits.

Jim Caudill
08-24-2006, 10:53 AM
For cutting, I usually use a 2:1 ratio. If I set the Aceytlene @ 5psi, then I set the Oxygen at 10psi. For welding, I set the pressures equal: somewhere around 10. I haven't tried using the 5:1 ratio reccomended by Torker, but it seems like a lot for Oxygen. It certainly wouldn't hurt to try some of these different combinations. Just observe the 15psi "red line" on your acetylene and play with the Oxygen (but I could never see any reason to go above 30psi).

Jim Caudill
08-24-2006, 10:58 AM
I just looked at the chart and it seems 20psi is the lowest reccommended pressure of cutting. Hmmm, maybe I've been doing it wrong all these years. Although I rarely cut anything over about 3/8" thick. What did we do before such technical information was widely available over the internet?

08-24-2006, 11:19 AM

the replies are popping up fast and furious.

dont be afraid to play with the oxygen pressure till its just right.

George Barnes
08-24-2006, 11:41 AM
When you are cutting a hole in the interior of a piece of plate, drill a small hole (1/8"-3/16") in that area. The cut will start much quicker and easier. Less gas usage and no popping.

08-24-2006, 12:29 PM
Don't forget, you still want a neutral flame at the torch.

5/25 rule is a good start for 1/4"

Light the acetylene to a feather that starts to smoke, slowly turn on the O2 to a neutral flame. Make sure your cutting O2 valve is fully open if you have one; bump the trigger a couple of times, reset to neutral.

If you want a pretty hole (you didn't say what size), clamp a disc a little undersize in place and use it for a guide.

Don't let your hose crawl under where you are cutting or the neighbors will get upset.

08-24-2006, 02:51 PM
I use this method. You can drill a start hole or burn one in as you start the cut. The cut will look better if you drill a start hole. I lite the gas and open to a good flame that is not blown off the tip. Then open the oxy knob and adjust both untill I get the size flame I want with a neutral flame. Then I depress the oxy cutting lever and adjust the flame to a neutral flame. Then I warm the metal and press the lever to start the cut. If the metal is not cutting good with a clean cut I increase the oxy knob at the cutting lever untill the burn is clean. You can do it while cutting or stop and adjust it. The Idea is to not have to much oxy when cutting. Just enough to do the job. It will take more for thick metal and less for thin. I usually set my acetylene to 5-7psi and the oxy 25-35psi.

Never weld or cut with gas and close the shop and leave. Always allow the parts and slag to cool and look around to see if anything is smoldering in surrounding areas where sparks flew.

Tin Falcon
08-24-2006, 04:54 PM
The Oxy fuel Welding,Cutting and heating Guide from Victor Thermadine is available free either as a PDF download or in print form from the local weling supply house.
Web link is http://www.thermadyne.com/victor/lit...dfs/70_2510.pd

08-24-2006, 05:42 PM
Thanks for all the tips guys, just making a plate for the tongue on my trailer project. It mounts the support jack. If it all looks good enough when I finish, I'll post a pic.


Jim Hubbell
08-25-2006, 04:01 AM
The above posts vary but I use 5psi acet and 20psi oxy. Quite a wide range of settings seem to get by. One area not touched on is " sharpening the cutting tip ". The center O2 orfice must be clean and have a sharp edge. It will be evident when the cutting valve is pressed. The stream of O2 should flow smoothly and not flare or twist to the side. The correct pressure for the tip size makes quite a difference.
Be careful and have fun.