MRO Magazine

Tips for stack burning and studs

When machine-burning a large number of parts from thin material, it is advisable to "stack-burn" the job. You old-timers out there know what I'm talking about. You stack up several layers of steel and...


September 1, 2000
By Frank C. Tabor

When machine-burning a large number of parts from thin material, it is advisable to “stack-burn” the job. You old-timers out there know what I’m talking about. You stack up several layers of steel and burn through all of them. This saves time, and gives a neater burn, eliminating the “slobbers” that form under the kerf when only one plate is burned at a time.

Stack burning does have its problems. Microscopic air spaces here and there between the sheets of plate will insulate your torch heat, causing a loss of your kerf in the centre of the stack and making a big mess out of the whole job. To prevent this, we clamp the plates together as tightly as possible and run weld beads across the edge to hold them.

However, that insulating air between the surfaces can be used to advantage on some applications. I will explain one instance where it came in handy after I go over another point in the process of acetylene burning.

Have you ever been confronted with the problem of burning a hole in thick plate when you didn’t have an electric drill along to make the initial hole for starting your cut? This was one of the many special operations I learned from the skilled people I worked with over the years. I’ve never seen this explained in books.

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Here’s how: Hold your torch in cutting position until the plate is red-hot. Then barely press the oxygen lever, and at the same time, slowly move your torch. As you move, gradually increase the oxygen pressure. I always jam one finger between the oxygen lever and the torch barrel to control the release of the oxygen. You experienced operators all know how fast that oxygen release will go down when tripped. As you travel, the slag will boil out onto the plate surface behind the tip, and you’ll only go a short distance before your cut has penetrated the plate. By doing it this way, you’ll never ruin a torch tip.

The principles and observation of the above two procedures are responsible for pulling me through a difficult repair situation — that and a little plain luck.

Two loggers came into our shop one morning and borrowed a cutting torch. Three hours later, they brought the torch back with a ruined tip, and a request for assistance to solve their problem. As usual, I turned out to be the goat, so I jumped into the repair truck and followed the loggers out to their operation. At the scene, when they told me to claw my way under a huge crawler tractor, I had a hunch I was in for a challenge.

On the frame of this particular “Cat” was a huge cross-member that was bolted between the tracks with six 3/4-in. cap screws on each side. Typical rough logging usage over the years had finally taken its toll by shearing off all of these bolts, leaving broken-off studs in the tapped holes. To further complicate the repair, the loggers had burned up our torch tip trying to burn out the broken ends. Being loggers and not welders, they had failed miserably and only added to the complications.

What’s that, Bunky? You say they should have welded nuts to the studs and screwed ’em out of there? Well, maybe yes and maybe no. That works sometimes when accessibility to a job is good, but, here we were, in close confinement, working in a prone position, and they had the studs recessed in their holes by the failed burning attempt. One look told me that it was either burn out those studs or take apart the whole Cat, haul it to town, and drill them out.

You burners know what happens when you try to burn in a hole. The torch gets overheated and suddenly starts a fast rat-a-tat-tat that would put Al Capone’s mob to shame. It was no doubt this factor that contributed to the loggers flunking out on their burning try. So, the first thing I did was to get a can of water to dunk the torch in when it sounded off. It took several dunkings of the torch per stud until I got them to a burning heat. Then, by using the penetration method described herein, I blew out all 12 broken-off bolt ends. The “air-insulation” factor worked to my advantage by letting the stud fragments burn out without doing serious damage to the threaded holes. A couple got hot enough to slightly nick the threads. I was able to chase the remaining residue with a 3/4-in. NC tap I had brought along.

I saved those guys several thousand dollars in repairs and downtime that day. Luckily, they were both busy chewing tobacco, or that might have been the closest I ever came to being kissed by a lumberjack.

Frank Tabor started his welding career by attending marine coppersmith school, then taught in the navy, worked in a long line of welding shops, and retired in 1986. Now, at 80, he’s a full-time cartoonist, something he’s always wanted to do. He combines his sense of humour and his industry knowledge in his stories and cartoons.

Do you have a solution for a maintenance problem? Send it in and if it’s published, we’ll send you a free Mr. O Problem Solver T-shirt an $35.00. Include your address and telephone number, print complete details, and add an illustration to help explain your tip. Send your ideas to Mr. O, Machinery & Equipment MRO, 1450 Don Mills Rd., Don Mills, Ont. M3B 2X7.