The one thing worse than breaking a bolt—and how to deal with it
Nothing allows you to safely use a tool or material outside of its design parameters quite like understanding how it works and preparing for what could go wrong. The freedom enjoyed by most people who work on cars comes from the ability to understand what they can change about a project—tools, materials, process—and what they cannot. While the tools and space you need to work on a given project are rigid, curiosity is endless and often leads you into interesting adventures.
My latest adventure was self-inflicted: I broke the head off a stuck bolt, a rite of passage for DIY enthusiasts. Some of you are even familiar with the second level of that situation, dealing with the broken “easy-out” screw extractor.
Some people take the easy way out (I will not apologize for that pun) and pay to replace the whole part. At first, it may have made sense to fix the broken bolt; when that little chunk of unobtanium easy-out became embedded in the bolt, the purse strings suddenly got a little looser.
An easy-out is not formed of unobtanium, though, but of high-carbon steel. Badass stuff in the metal world. It is hard, enabling it to bite into and grab a mutilated bolt—a problem we never admit to creating but always boast about fixing. On the Rockwell hardness scale, high-carbon steel falls in the middle of the chart. Even so, the material is very brittle—and not in the delicious way, like the peanut brittle Nana used to make. If you introduce a fraction of a side load while using an extractor, you will snap it off—often flush with your workpiece—leaving you defeated.
At least partially defeated. Now comes the escalation of force, the switch from rigid to flexible. Solving the problem of a broken extractor requires understanding the materials you are dealing with. If you rush ahead, you will end up with a mangled part and a pile of dull drill bits.
The last time I broke an easy-out, I immediately picked up the phone instead of the tools. This time, I couldn’t bring myself to call for more experienced assistance. I needed to deal with this myself.
I have a drill press sitting on my shop floor. It’s not the Bridgeport of my dreams, but it’s decent, and the more I looked at it, the more I realized this drill press had the capability I needed. With a little effort, I could build a good, rigid setup—enough to drill a right-angle hole, at least. If I could figure out how to fix this broken extractor myself, the process would likely bestow upon me the knowledge and experience to avoid this whole song and dance again. The catastrophe you are prepared for rarely strikes, right? Off to McMaster-Carr to buy some carbide.
Carbide is the next step up from high-carbon steel on the Rockwell hardness scale, which means it can pierce high-carbon steel without losing its edge. I selected two sizes of end mills made of carbide. With 90-degree tips designed specifically for plunge cutting, they should be able to remove not only the easy-out but also the bolt—and, likely, a decent amount of the aluminum of my workpiece, a case cover.
That last part was unfortunate but acceptable. Installing new threads or repairing those that remained would be easier than trying to save the delicate M6 threads. Not only were they formed decades ago, but, since they were on the oil-filter cover, they had also suffered hundreds of hamfisted tightenings and overtorques. Thread forms distort with multiple uses, especially when they are made of aluminum, so the thought of new threads in this piece was almost a little comforting. Doing the thread repair with the case cover off the motorcycle and on the bench was an obvious plus.
Carbide in hand, I had to think about setup. Luckily, the table of my drill press has T-slots in it to help the user create a more rigid setup. However, I could only do so much—especially after realizing there was no place locally to source T-nuts. My plan switched to going through my drawer of random hardware until I found the right combination of bolts and nuts. Finally, I had fastened the side cover to the table at three points. I then wound the table as high as I could to keep the quill as high and stiff as possible. The name of the game was rigidity. (This is not to be attempted with a cordless drill.)
With a little cutting oil to keep things cool, I started pecking at the cover with the lever that controlled the quill of the press. The 90-degree tip of the end mill enabled me to carefully locate the actual center—not the poorly drilled hole now filled with easy-out—and begin to remove material. It was a delicate game of managing speeds and feeds by hand: I had to put enough downward pressure on the end mill to prevent chatter—the cutting faces skipping along the surface of the material rather than biting into it—but not so much pressure that I began to generate heat.
Applying cutting oil and taking breaks every few minutes made the whole process feel like it took forever, but it was really maybe 10 minutes of actual work stretched across an hour, me stressing the whole time about breaking the end mill. That would all but require me to call for help, and I would not be real proud to carry this mess into someone else’s workspace.
Of course, the end mill broke. Luckily, there was plenty sticking up, so I grabbed what remained and yanked out the end-mill. With a small punch, I knocked the leftover easy-out onto the bench, which allowed me to step up to the 6.4mm bit to cut the final diameter of the hole. I used a tap to form threads and the repair was complete.
There were a number of ways to go about solving that last piece of the problem, but mine was the most final. The re-formed threads would fail at the same rate as the OE production ones—good enough, considering that the other two bolts for this oil filter cover are original threads.
In the garage, there are some rigid concepts that define the ways we can do things. High-speed steel will not drill out a carbide end mill; that is fact. How you use this knowledge, however, is highly variable. Once you understand the facts that constrain a project, your brain can switch fully to creative thinking and problem-solving. The materials I use demand to be used a certain way; knowing that enables me to choose the right tool for the job or, when doing something off-piste, to stack the deck in my favor. The combination of the flexible and inflexible will set your project free. It is the workbench yin and yang.