Cutting torch help ??

[mhorowit]

Using an OA rig, I've been successful in making puddles and moving them across a piece of 1/8" steel. Now I'd like to cut some with the torch.
It's a small tip, O2@10-15psi, acetylene at 2-3 psi.
Heat up the metal and gently squeeze the O2 lever. Cut begins, but immediately closes up behind the hole, filling up the kerf.
Anyone got an idea what's happening? - Mike

[birdlegs]

Re: Cutting torch help ??

Mike; after you've made a pierce with the oxidizer try moving quicker,it sounds like you're re-welding the hole or you need more psi @ the oxy orfice
even w/ thin base metal it needs some o2 w/ psi behind it. Brad

[mhorowit]

Re: Cutting torch help ??

Mike; after you've made a pierce with the oxidizer try moving quicker,it sounds like you're re-welding the hole or you need more psi @ the oxy orfice even w/ thin base metal it needs some o2 w/ psi behind it. Brad

Even if I use a working pressure of greater than 15psi of O2, I still need a neutral flame; what does increasing the working pressure do? Increase the velocity? - Mike

[Guest]

Re: Cutting torch help ??

Using an OA rig, I've been successful in making puddles and moving them across a piece of 1/8" steel. Now I'd like to cut some with the torch.
It's a small tip, O2@10-15psi, acetylene at 2-3 psi.
Heat up the metal and gently squeeze the O2 lever. Cut begins, but immediately closes up behind the hole, filling up the kerf.
Anyone got an idea what's happening? - Mike

Hi Mike, follow the specs for the torch, 15 psi sounds way low. The torch manual should give some settings for acetylene & ox. Acetylene will allways be less than 14 psi and ox will likely be 25 to 35 psi.

Light the torch this way. close the ox valve on the cutting attachment, then open the ox valve on the torch handle a number of turns so it is not restricting flow, then open the acetylene valve just a little on the torch handle and light the tip, it should make soot then open the acetylene valve slowly until the flame does not produce soot, that is the proper actetylene valve setting, then open the ox valve on the cutting attachment slowly to produce a neutral flame. After this when you push the cutting lever you should see a change in the flame from the excess ox. When you then apply the flame to metal and it gets red pushing the cutting lever is supposed to inject excess ox to burn thru the metal.

If you find that the flame is to hot or cold after adjusting it this way go get a smaller or larger tip from your welding supply.

After all that let me ask this; why are you using a cutting torch? That's for tractors and automobiles!

My opinion is that on an a/c frame a hacksaw and a high speed cut off wheel will serve you best. A cutting torch can do a lot of damage. I never use on on an a/c. Of course you may be just practicing the art.

Also if you plan on welding tubes then after you master the puddles on 1/8" go down to 1/16" and after that get some tubing and start on it by making splices and patches and also make some clusters. The .027 to .049 wall is going to be a little different than the 1/8 or 1/16. Wicks Aircraft sells (or used to) practice bundles of short pieces just for that purpose.

Hope this helps.

Dave.

[mhorowit]

Re: Cutting torch help ??

Mike...
... quit screwing around with the O/A set up until you have a decent idea of what you are doing.... READ THE BOOK. ... It is reallly dumb simple if you follow the rules.

Ron - please see my private e-mail - Mike

[mhorowit]

Re: Cutting torch help ??

Hi Mike, follow the specs for the torch,

Light the torch this way.

After all that let me ask this; why are you using a cutting torch? That's for tractors and automobiles!

Of course you may be just practicing the art.

Wicks Aircraft sells (or used to) practice bundles of short pieces just for that purpose.

Hope this helps.

Dave.

Specs: problem is the tip is battered and we don't know the size, although welding clerk sez it's relatively small. If we had documentation, we'd be set, as it is, we need to experiment to get the right settings. What I got now is symptoms.

Lighting: that's my procedure.

Cutting torch: Agreed, it has no place near an a/c. However (once I find the correct settings) it is also useful for cutting heavy angle iron for making a welding stand.

Practicing: bingo

Scrap: 10# of 4130 from Spruce in a box in the living room, but I want to practice on 1/8" until I"ve regained my basics.

- Mike

[paulnuss]

Re: Cutting torch help ??

Your problem is too much pre-heat to the relatively thin gauge metal, and/ or too slow a travel speed. You are melting a lot of metal around the cutting kerf, which is flowing back together after you pass by. The pressure settings vary with the manufacturer, but 3-5 psi acetylene and 20-25 psi oxygen should be in the ballpark with most. Lighting and neutral flame descriptions above were correct. I used to sell a "light preheat" or "sheet metal" cutting tip to help with the problem mentioned. A sheet metal cutting tip (probably only a rare welding supply house, owned by an old geezer as mentioned above, will stock them) has one small preheat orifice and one cutting orifice, designed to be used with the preheat leading, the cutting orifice following, dragging at the angle built in to the tip and the stand-off built into the tip. Lacking one of those, a light-preheat tip, constant hold stand-off distance, and adequate travel speed will get you to a reasonable result.

Any resemblance by me to the "old geezer" mentioned above is purely coincidental!

[alwaysoar]

Re: Cutting torch help ??

Check with the local tech school continueing ed department. Most of them offer intro welding classes.

[mhorowit]

Re: Cutting torch help ??

Your problem is too much pre-heat to the relatively thin gauge metal, and/ or too slow a travel speed. You are melting a lot of metal around the cutting kerf, which is flowing back together after you pass by. The pressure settings vary with the manufacturer, but 3-5 psi acetylene and 20-25 psi oxygen should be in the ballpark with most. Lighting and neutral flame descriptions above were correct. I used to sell a "light preheat" or "sheet metal" cutting tip to help with the problem mentioned. A sheet metal cutting tip (probably only a rare welding supply house, owned by an old geezer as mentioned above, will stock them) has one small preheat orifice and one cutting orifice, designed to be used with the preheat leading, the cutting orifice following, dragging at the angle built in to the tip and the stand-off built into the tip. Lacking one of those, a light-preheat tip, constant hold stand-off distance, and adequate travel speed will get you to a reasonable result.

Any resemblance by me to the "old geezer" mentioned above is purely coincidental!

I'll try the higher working pressure for O2 tonite - Mike

[Carl Ellis]

Re: Cutting torch help ??

Mike -

There are a couple of good books you might like:

EAA "How To" Series
Aircraft Welding/The Art of Welding

Welder's Handbook
A complete guide to MIG, TIG, ARC and Oxyacetylene welding
Richard Finch

I believe that I purchased both through Aircraft Spruce.

- Carl -

[mhorowit]

Re: Cutting torch help ??

Mike -

There are a couple of good books you might like:

EAA "How To" Series
Aircraft Welding/The Art of Welding

Welder's Handbook
A complete guide to MIG, TIG, ARC and Oxyacetylene welding
Richard Finch

I believe that I purchased both through Aircraft Spruce.

- Carl -

carl - I have Finch's book in front of me and his book "performance Welding" on the way from Lindsey's books.

This problem is going to turn out to be crantking the O2 to #25, you watch. - Mike

[Guest]

Re: Cutting torch help ??

Hi Mike, hope things are working for you now.

I got some documents for my Smith torches by calling Smith and they sent me manuals for it.

Perhaps Harris, Airco... and the other manufacturers provide a similar service.

I like Finch's books. I have the two you purchased also. I recall that Finch is the guy who re-wrote the welding section of ac43.13-1b.

I got a book from the Lincoln Welding Foundation Foundation called "Metals and how to Weld Them" for less than $10, very good book.

The defense department also publishes many books on welding "Military Handbook 58, Thermal Joining of Metals Other Than Arc Welding" and there is one on arc welding too. Check out this gov site, you can find teh handbook plus more there http://assist.daps.dla.mil/wizard/. You may have to register first. If/when you search use CAPITALS, it seems to be case sensitive.

Good welding, Dave.

[mhorowit]

Re: Cutting torch help ??

Thank you for your private reply:

Ron - I was trying to keep it private - MIke