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Common Tread

No extractors or penetrating lube in sight: How the pros remove sheared bolts and bits

Dec 27, 2022
“I drill out broken bolts, and burn out everything else,” says Eric Grafton, standing beside a Ferrari engine block and an elaborate piece of billet-steel industrial equipment, both of which have a threaded hole with the dull sheen of sheared metal peeking out of them. 

By “everything else” Eric means broken taps and other hardened tools that won’t succumb to the cutting edge of a drill bit, and by “burn out,” he means disintegrate with an MDM machine, which looks like the offspring of a drill press and a MIG welder.  

A metal disintegrator may sound like a spaceship-destroying sci-fi weapon, but it’s actually a piece of shop equipment used to remove broken bolts, taps, and drills. The technology was invented in the 1940s. This 15 kVA machine is from the mid-1960s. Photo by Ari Henning.

Metal disintegration machining, or MDM, uses intermittent electric arcs at the end of a vibrating electrode to break down metals into minute particles that are flushed away by dielectric fluid. “The vibration keeps the electrode from welding, and the interaction between the heat and cooling is what disintegrates the metal,” says Eric. MDM is a remarkable, rare, and surprisingly old technology that I knew nothing about until I’d exhausted DIY options for removing a broken stud from a 50-year-old cylinder. 

Bolt broken in a component.
They say every 20-minute job is a broken bolt away from becoming a three-day ordeal. When all else fails, MDM can save the day, and the component. Photo by Ari Henning.

In desperation, I reached out to a local machine shop for help, and was told to “call Jerry.” They were referring to Jerry’s Broken Drill and Tap Removal in Santa Ana, California, which was opened by Gerold “Jerry” Grafton in 1963 and is now run by Jerry’s grandson, Eric.

Jerry’s is just one of a handful of places in the United States that provide MDM services to the public, since the specialized and expensive disintegration machines are typically the domain of corporations. “Most of the facilities with my equipment are 75- to 100-man shops that manufacture and maintain things like nuclear reactors and ship engines,” says Henry Cammann, whose company built the MDM machines that Jerry bought in the 1960s and Eric still operates today. 

Massive reactor studs removed with MDM.
"We make machines that can take out seven-inch reactor studs, 14 inches deep," says Henry Cammann of Cammann Metal Disintegrators. Photo by Henry Cammann.

Jerry’s certainly isn’t a giant of industry, but it served SoCal’s aerospace behemoths for decades and is still a lifesaver for many local companies and individuals across the country. There is no PB Blaster or EZ-Outs in sight at Jerry’s. Instead, Eric has three Cammanns (a large, small, and portable unit), a variety of pneumatic drills, and a dust-caked grinder that he uses to keep a fine edge on his bits. 

“Drilling does the same thing as the machines, and I don’t have to pay for electrodes,” says Eric. Whether he’s using MDM or a twist bit, the objective is to hollow out the offending object to within a hair of its outer diameter, then remove the remaining material by carefully picking and chiseling it away with a pick that Eric fashions from a hardened drill blank. 

A piece of industrial equipment that has a broken tap.
Repair it, or scrap it? The cost and replaceability of the part is the determining factor, and this piece of equipment looks pricey! The note "1/2-13 1.400 deep," specifies the size and depth of the offending obstruction, which in this case is a tap. Photo by Ari Henning.

Often, the original threads are left intact, though sometimes they need to be chased, or, in rare instances, replaced. “If I get a workpiece where somebody has already drilled it way off center,” explains Eric, “I may have to oversize the hole, turn a plug on the lathe, and then install and thread that.”

Drilling works for softer materials like the steel used in bolts and studs, but for Eric’s most common job — Harley heads with broken exhaust studs — burning is the method of choice since the studs are so long and the heads are so hard to get square.

Broken bolt removed with an extractor.
Without the tension imparted by a bolt’s head, the shaft can often be removed with a left-hand drill bit or spiral extractor. However, if the bolt threads are seized, “you’re probably not going to have any luck getting it out by drilling a little hole in the middle and using something brittle to turn it,” says Eric. Photo by Ari Henning.

“Setup is everything,” says Eric, who has both an extremely steady hand as well as a variety of jigs and guides to keep his drill on course. The Cammanns have a slotted bed for securing and truing the workpiece, and the tool head travels a set path, so the operation is very precise. Even though burning is more expensive “it’s a lot easier,” says Eric. 

Thread remnants and a pick.
Evidence of a successful extraction. Eric's drill-and-pick approach is possible to employ at home, but works best on short, large-diameter obstructions. I used it on a rust-welded 14 mm bolt that sheared off in the frame of my dad's car. Photo by Ari Henning.

When it comes to broken drill bits and taps, burning is the only option, and the MDM equipment makes quick work of the material. Even with such specialized equipment, Eric says the jobs are often challenging. “I get stuff with multiple holes, multiple snapped EZ-Outs, and it’ll be melted from a torch, but those are the ones I enjoy most. That’s when I have to get creative, and the fix feels like art.”  

Hollow MDM electrodes and a burned stud.
For larger removals, a hollow graphite electrode like those in the foreground is used. The eroded rod is what’s left of a stud after burning out. For this reason, MDM is also used in metallurgical applications for obtaining core samples of a material. Photo by Ari Henning.

For the end user, the cost is typically about $80 to $100 a hole. That’s not cheap, but if you’ve exhausted your options or your Plan B just snapped off in the project, MDM machining is a surefire way to make things right.