Can you drill out a bolt? Yes, you can drill out a bolt. This guide will show you how to safely and effectively drill out a stubborn or broken bolt.
When a bolt breaks off flush with a surface, or becomes so corroded or overtightened that it strips, it can feel like a major roadblock. Fortunately, with the right tools and techniques, you can learn how to drill a bolt out and overcome this common mechanical challenge. This process is essential for anyone looking to repair or maintain machinery, vehicles, or even household items. It allows you to remove damaged fasteners without causing further harm to the surrounding material.
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Tools You Will Need
Gathering the right tools before you start is crucial for a successful bolt removal. Having everything on hand will prevent interruptions and ensure you have the proper equipment for each step.
- Safety Gear:
- Safety Glasses: Absolutely essential to protect your eyes from flying debris.
- Work Gloves: To protect your hands from sharp edges and heat.
- Marking and Centering Tools:
- Center Punch Bolt: This tool creates a small indentation, guiding your drill bit to the exact center of the bolt, preventing it from wandering.
- Marker or Pen: To clearly mark the bolt.
- Drilling Equipment:
- Drill (Corded or Cordless): A powerful drill is necessary for consistent drilling. Corded drills often provide more sustained power.
- Drill Bits:
- Reverse Drill Bit: These bits are specifically designed to cut while the drill is in reverse. As they bite into the metal, they can sometimes unscrew the broken bolt on their own.
- Regular High-Speed Steel (HSS) Drill Bits: You’ll need a set of bits, starting small and gradually increasing in size.
- Drill Press (Optional but Recommended): For increased accuracy and stability, especially for larger bolts or when drilling into delicate materials.
- Extracting Tools:
- Bolt Extractor Kit: This is a set of specialized tools designed to grip and remove broken bolts. They often work by being hammered into a drilled hole and then turned.
- Pliers (Vise-Grips or Locking Pliers): Useful for gripping any protruding part of the bolt.
- Lubrication and Cleaning:
- Cutting Fluid for Metal: This lubricant reduces friction and heat, making drilling easier and extending the life of your drill bits. It also helps prevent galling.
- Wire Brush: For cleaning away debris.
- Thread Repair (If Necessary):
- Tap and Die Set: If the original bolt hole is damaged, a tap can be used to re-thread the hole.
- Replacement Bolt: Once the old bolt is out, you’ll likely need a new one.
Step-by-Step Guide to Drilling Out a Bolt
Follow these steps carefully to maximize your chances of successfully removing the broken bolt. Patience is key in this process.
Step 1: Assess the Situation and Prepare the Area
Before you start drilling, take a moment to look at the broken bolt.
- How much of the bolt is remaining? Is it flush, slightly raised, or completely recessed?
- What material is the bolt in? This will affect the drilling speed and pressure you can apply.
- Is the bolt accessible? Ensure you have enough space to work comfortably and safely.
Prepare the surface around the bolt:
- Clean the area thoroughly with a wire brush to remove any dirt, rust, or debris.
- Ensure the surface is as flat and clean as possible.
Step 2: Center Punch the Bolt
This is a critical step for accurate drilling. A misplaced drill bit can damage the surrounding material or create an off-center hole that’s harder to manage.
- Place the tip of the center punch bolt directly on the center of the broken bolt.
- Strike the end of the center punch firmly with a hammer. You don’t need to create a deep hole, just a small, visible indentation.
- If the bolt is broken flush, try to center the punch as precisely as possible. If it’s slightly raised, aim for the center of the remaining portion.
Step 3: Start Drilling with a Small Pilot Hole
Using a drill bit that is significantly smaller than the bolt’s diameter is essential. This pilot hole will guide your larger bits and any extraction tools.
- Select a small, sharp HSS drill bit (e.g., 1/8 inch or 3mm).
- Place the tip of the drill bit into the indentation created by the center punch.
- Hold the drill steady and at a 90-degree angle to the surface.
- Begin drilling at a slow speed, applying steady, consistent pressure.
- Use cutting fluid for metal as you drill. Apply a few drops directly to the bolt and the drill bit. This will help keep the bit cool and lubricated, making the drilling process smoother and preventing the bit from overheating.
- Drill a hole that goes about halfway through the length of the broken bolt, or as deep as you can manage without hitting the threads of the mating material.
Step 4: Gradually Increase Drill Bit Size
Once you have a clean pilot hole, you’ll need to enlarge it. The goal is to get close to the diameter of the bolt’s shank but avoid damaging the threads in the hole.
- Choose a slightly larger drill bit than your pilot hole.
- Repeat the drilling process: center the bit, use cutting fluid, drill at a slow to moderate speed with steady pressure.
- Continue to step up the drill bit size incrementally.
Important Consideration for Drill Bit Sizing:
| Bolt Diameter (Approx.) | Initial Pilot Drill Bit | Final Drill Bit (Before Extractor) |
|---|---|---|
| 1/4 inch (6mm) | 1/8 inch (3mm) | 7/32 inch (5.5mm) |
| 5/16 inch (8mm) | 3/16 inch (5mm) | 1/4 inch (6mm) |
| 3/8 inch (10mm) | 1/4 inch (6mm) | 5/16 inch (8mm) |
| 1/2 inch (12mm) | 5/16 inch (8mm) | 3/8 inch (10mm) |
Note: The final drill bit size should be just under the minor diameter of the bolt’s threads to avoid damaging the original threads.
Step 5: Using a Bolt Extractor Kit
This is where specialized tools come into play to help extract broken bolt pieces.
- If using a reverse drill bit: Continue drilling with the largest bit you’ve used, but ensure your drill is set to REVERSE. The reverse rotation might catch the bolt and unscrew it as you drill.
- If using a standard extractor:
- Select the appropriate size bolt extractor kit bit. These are typically tapered and have a reverse spiral thread.
- Gently tap the extractor into the drilled hole with a hammer. It needs to bite into the metal of the broken bolt.
- Attach a wrench or a bolt removal tool (like a tap wrench or socket) to the extractor.
- Slowly and steadily turn the extractor counter-clockwise.
- Apply firm, even pressure. You should feel the extractor biting into the bolt.
- If the extractor starts to slip, you may need to tap it in a bit deeper or use a larger extractor.
Step 6: Alternative Method: Drilling Out the Entire Bolt
If an extractor doesn’t work or you don’t have one, you can drill out the entire bolt. This method requires precision to avoid damaging the threads of the hole. This is often referred to as needing to drill out stripped bolt when the head is gone.
- Continue increasing your drill bit size until the diameter of your hole is very close to the outer diameter of the bolt’s threads.
- The goal is to drill away the bolt material without touching the threads of the hole.
- As you get close to the thread diameter, you might be able to carefully pick away the remaining bolt material with a scribe or a small chisel.
- Once the bulk of the bolt is drilled out, you can try to gently tap the remaining thread fragments out with a pick.
Step 7: Using an Impact Driver for Bolt Removal (Caution)
An impact driver bolt removal technique is generally not recommended for drilling out a bolt when the head is gone. Impact drivers are designed to provide rotational force combined with blows, primarily for loosening seized but intact fasteners. For drilling, a regular drill or drill press is preferred for control. However, if a small piece of the bolt is protruding and you’ve managed to grip it with locking pliers, an impact driver might be used cautiously on the pliers to help turn it, but this carries a high risk of breaking the pliers or further damaging the bolt or surrounding material.
Step 8: Cleaning and Re-threading
After the broken bolt is removed, you’ll need to clean up the hole.
- Use a wire brush to clean out any remaining metal fragments from the bolt hole.
- If the threads in the hole are damaged, you’ll need to use a tap and die set.
- Select the correct tap size for the original bolt thread.
- Apply cutting fluid for metal to the tap.
- Insert the tap into the hole and turn it clockwise, backing it out periodically to clear shavings and reapply fluid. This will recut or clean the existing threads.
- Once the threads are clean or re-tapped, you can install a new bolt.
Common Problems and Solutions
Even with the best intentions, you might encounter a few snags. Here’s how to address them:
- Drill Bit Wandering:
- Problem: The drill bit doesn’t start in the center and walks across the bolt surface.
- Solution: Ensure you’ve made a good, deep indentation with your center punch bolt. Start with a very small pilot hole. Consider using a drill guide if available.
- Overheating Drill Bits:
- Problem: The drill bit gets very hot, making drilling difficult and potentially damaging the bit.
- Solution: Use plenty of cutting fluid for metal. Drill at slower speeds and retract the bit periodically to clear shavings and allow it to cool.
- Extractor Slipping or Breaking:
- Problem: The extractor bites but slips, or worse, breaks off inside the bolt, making the situation much more difficult.
- Solution: Ensure you’ve drilled the correct size hole for the extractor. Tap the extractor in firmly but don’t overdo it. If it breaks, you may need to drill it out with a carbide bit, which is very difficult. Sometimes, a small piece of metal can be welded to the broken extractor to try and turn it out.
- Damaging Threads:
- Problem: The drilling process removes too much material, damaging the threads of the hole.
- Solution: This is why precise drilling and using the correct final drill bit size is crucial. If threads are damaged, you will need to use a tap and die set to recut them. For severely damaged threads, you might need a thread repair insert like a Heli-Coil.
- Bolt is Too Soft and Galls:
- Problem: The bolt material is very soft and the drill bit causes it to deform and “gum up” the hole instead of cutting cleanly.
- Solution: Use very sharp drill bits, keep them cool with plenty of cutting fluid for metal, and drill at slower speeds. Ensure your drill is set to a sturdy RPM.
When to Call a Professional
While this guide equips you to handle many situations, some scenarios might be best left to the experts.
- Irreplaceable Parts: If the component the bolt is threaded into is rare, expensive, or irreplaceable, and you’re not confident in your abilities, it might be safer to seek professional help.
- Extremely Seized Bolts: In some cases, bolts are so fused with corrosion or overtightening that even the best tools and techniques struggle.
- Very Small or Delicate Components: Working with tiny fasteners on sensitive electronics or intricate machinery requires a very delicate touch and specialized tools that go beyond a standard home workshop.
- Broken Extractors: If an extractor breaks off inside the bolt, this is a very difficult situation to resolve without specialized equipment and expertise.
Conclusion
Learning how to drill a bolt out is a valuable skill for any DIY enthusiast or mechanic. By carefully following these steps, using the right tools like a bolt extractor kit or reverse drill bit, and prioritizing safety, you can successfully remove seized bolt and get your project back on track. Remember that patience and precision are your greatest allies in this process. Whether you’re dealing with a stripped head or a bolt broken below the surface, this guide provides a clear path to a solution.
Frequently Asked Questions (FAQ)
Q1: What is the best way to remove a broken bolt?
A: The best way depends on how the bolt is broken. If a portion is sticking out, locking pliers might work. If it’s flush or recessed, drilling it out and using a bolt extractor is a common and effective method.
Q2: Can I use a regular drill bit to remove a bolt?
A: Yes, you can start with regular high-speed steel (HSS) drill bits for a pilot hole, but for extracting a broken bolt, a reverse drill bit or the use of a bolt extractor kit is usually necessary to turn the bolt out.
Q3: How do I prevent damaging the threads when drilling out a bolt?
A: Use a center punch bolt for accuracy, start with a small pilot hole, gradually increase drill bit size, and stop drilling when your bit reaches the diameter of the bolt’s minor thread diameter (the smallest part of the thread). Always use cutting fluid for metal.
Q4: My bolt extractor broke off in the bolt. What do I do?
A: This is a very challenging situation. You’ll need to try and drill out the broken extractor itself, which requires extremely hard drill bits (like carbide) and great care. It’s often best to seek professional help at this point.
Q5: What is the purpose of cutting fluid?
A: Cutting fluid for metal reduces friction and heat during drilling, prolongs the life of your drill bits, helps clear metal shavings, and can prevent galling of the metal being drilled.