How To Drill Out Stripped Bolt: Step-by-Step - Daily Hand Tools: Your Everyday Guide

A stripped bolt is a common and frustrating problem, but can I drill out a stripped bolt? Yes, you absolutely can, and this guide will walk you through it. This guide is designed to help you tackle a stripped bolt with confidence, even if you’re not a seasoned mechanic. We’ll cover everything you need to know, from gathering your tools to the final successful removal.

How To Drill Out Stripped Bolt
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Why Bolts Get Stripped

Bolts can become stripped for several reasons. Over-tightening is a primary culprit, as it can deform the bolt head, making it difficult to grip with standard tools. Using the wrong size wrench or socket can also round off the bolt head. Corrosion and rust can seize a bolt in place, and when force is applied to a stuck bolt, the head can strip. Sometimes, poor quality bolts themselves are prone to stripping.

Essential Tools for Bolt Removal

Before you begin, gather all the necessary tools. Having everything ready will make the process smoother and safer.

Tool Checklist:

Safety Glasses: Always wear safety glasses to protect your eyes from flying debris.
Gloves: Protect your hands from sharp edges and grease.
Center Punch: To mark the exact center of the bolt.
Hammer: To strike the center punch.
Drill: A corded drill often provides more consistent power than a cordless one for this task. An impact driver can also be helpful in some situations, but for drilling, a standard drill is generally preferred.
Drill Bits:
- Drill bits for metal: You’ll need a set of high-quality drill bits for metal. Start with a small bit and gradually increase the size.
- Left-hand drill bit: A left-hand drill bit (also known as a reverse drill bit) is a specialized bit that drills counter-clockwise. This can sometimes catch the bolt and unscrew it as you drill.
Drill Bit Size Chart: It’s helpful to have a drill size for bolt chart available to select the correct bit sizes as you progress.
Bolt Extractor Set: This includes various sizes of extractor bolt bits, which have a spiral flute designed to bite into the metal of the stripped bolt.
Penetrating Oil: To help loosen a stubborn or corroded bolt.
Grinding Wheel or Flap Disc (Optional): For creating a flat surface or slots if the bolt head is severely damaged.
Vise Grips or Locking Pliers: For gripping any part of the bolt head that might still be accessible.
Shop Towels: For cleaning up.

Step-by-Step Guide to Drilling Out a Stripped Bolt

Here’s a detailed breakdown of the process. Patience and precision are key.

Step 1: Assess the Damage and Prepare the Area

First, take a close look at the stripped bolt. How badly is the head damaged? Is it completely rounded, or is there still a slight indentation you might be able to grip?

Clean the Area: Remove any dirt, grease, or debris from around the bolt. This will give you a clearer view and prevent contaminants from entering the drilled hole.
Apply Penetrating Oil: Spray a generous amount of penetrating oil onto the bolt threads. Allow it to soak for at least 15-30 minutes, or even longer if the bolt is very stubborn or rusted. This can help loosen the bolt’s grip.

Step 2: Center Punching the Bolt

This is a crucial step to ensure your drill bit goes in straight and doesn’t wander.

Position the Center Punch: Place the tip of the center punch directly in the center of the stripped bolt head.
Strike with a Hammer: Give the end of the center punch a firm tap with the hammer. You don’t need to punch all the way through the bolt, just create a small dimple. This dimple will guide your drill bit. If the bolt head is severely rounded, try to create the dimple in the flattest part of the remaining head.

Step 3: Starting the Pilot Hole

You’ll begin by drilling a small pilot hole into the center of the bolt.

Select a Small Drill Bit: Choose a small drill bit for metal that is significantly smaller than the diameter of the bolt. A good starting point might be 1/8 inch (3mm) or 3/16 inch (4mm).
Set Your Drill: If your drill has a clutch, set it to a low torque setting. This will help prevent you from accidentally breaking the drill bit. Ensure your drill is set to its normal forward (clockwise) rotation.
Drill Slowly and Steadily: Place the tip of the drill bit into the dimple created by the center punch. Apply firm, steady pressure. Let the drill do the work. Avoid pushing too hard, as this can cause the bit to break or wander.
Keep it Straight: It’s vital to keep the drill perfectly perpendicular (straight up and down) to the bolt head. If the hole goes in crooked, it will be much harder to use an extractor later.

Step 4: Progressing to Larger Drill Bits

Once you have a pilot hole, you’ll gradually increase the drill bit size.

Choose a Larger Bit: Select a drill bit that is slightly larger than your pilot hole but still smaller than the diameter of the bolt itself. Again, refer to your drill size for bolt chart.
Drill Again: Repeat the drilling process, ensuring the bit is centered and drilling straight. Use a bit of cutting fluid or oil to help lubricate the bit and the bolt as you drill. This reduces heat and makes drilling easier.
Continue Gradually: Continue stepping up the drill bit size. The goal is to drill a hole that is substantial enough to accommodate your chosen extractor bolt.

Step 5: Using a Left-Hand Drill Bit (Optional but Recommended)

A left-hand drill bit (also called a reverse drill bit) can sometimes be the easiest solution.

Select a Left-Hand Bit: Choose a left-hand drill bit that is the same size or slightly larger than the last bit you used.
Set Drill to Reverse: Ensure your drill is set to its reverse (counter-clockwise) rotation.
Drill Slowly: Place the reverse drill bit into the pilot hole. As you drill counter-clockwise, the bit might catch the inside of the bolt. If it does, the bolt might start to unscrew itself!
Apply Pressure: Apply steady pressure. If the bolt starts to turn, continue gently until it’s out. If it doesn’t turn, you’ve successfully enlarged the hole for an extractor.

Step 6: Employing a Bolt Extractor

If the bolt hasn’t come out with a left-hand drill bit, it’s time to use a specialized extractor bolt tool.

Choose the Right Extractor: Select an extractor bolt that is appropriately sized for the hole you’ve drilled. The extractor should fit snugly into the drilled hole.
Insert the Extractor: Gently tap the extractor bolt into the drilled hole with a hammer. It should seat firmly.
Use a Wrench or Ratchet: Attach a wrench or ratchet to the end of the extractor bolt.
Turn Counter-Clockwise: Slowly and steadily turn the wrench or ratchet counter-clockwise. The reverse threading of the extractor will bite into the bolt and, with luck, unscrew it.
- Apply even pressure: Avoid jerky movements.
- Listen for movement: You might hear or feel the bolt begin to turn.
- If it breaks: If the extractor snaps off inside the bolt, you have a more complicated problem, as extractors are made of hardened steel and are very difficult to drill out. This is why using the correct size extractor and applying steady pressure is so important.

Step 7: Alternative Methods for Severely Damaged Bolts

If the bolt head is so badly damaged that you can’t get a good center punch or drill straight, you might need alternative approaches.

Using a Grinding Wheel

If the bolt head is completely rounded and offers no purchase for a center punch, you might need to create a new slot.

Safety First: Put on your safety glasses and gloves.
Use a Grinding Wheel or Flap Disc: Attach a grinding wheel or flap disc to your drill or an angle grinder.
Create a Slot: Carefully grind a straight slot across the top of the bolt head. This slot should be deep enough to accept a flathead screwdriver or a chisel.
Attempt Removal: Once the slot is created, try to remove the bolt using a large flathead screwdriver and a hammer, or a chisel and hammer. You might also be able to use a Dremel with a cutting disc.

Using Vise Grips

If there’s any part of the bolt head still protruding, you can try using Vise Grips.

Grip Tightly: Clamp the Vise Grips onto the bolt head as tightly as possible.
Turn Slowly: Try to turn the bolt counter-clockwise. If the bolt head starts to deform further, stop.

Step 8: Final Removal and Cleanup

Once the bolt is out, clean up the threads.

Clean the Threads: Use a wire brush to clean any remaining bolt fragments or debris from the threaded hole.
Chase the Threads (Optional): If the threads are damaged, you can use a tap of the correct size to clean them up or re-thread them. Be sure to use cutting fluid when tapping.

Troubleshooting Common Problems

Even with the best preparation, you might encounter difficulties.

My Drill Bit Broke Inside the Bolt

This is a common and frustrating problem. Hardened steel drill bits, especially smaller ones, can snap if too much force is applied or if they get too hot.

What to Do: If a standard drill bit breaks, you’ll need to try and drill it out with a carbide bit, which is harder. Alternatively, you might be able to carefully use a small grinding wheel on a rotary tool to grind down the broken bit. If a hardened extractor bolt breaks, this is much more serious. You may need to resort to specialized carbide drill bits, or even attempt to grind away surrounding material to relieve pressure on the broken extractor.

The Extractor Broke Off in the Bolt

This is a worst-case scenario because hardened steel extractors are very difficult to drill through.

What to Do:
- Carbide Bits: Your best bet is to try and drill out the broken extractor with a very hard carbide drill bit.
- EDM (Electrical Discharge Machining): For critical applications where success is paramount, a machine shop can use EDM to remove the broken extractor without damaging the surrounding material. This is a professional service.
- Grinding: In some cases, if the extractor is just below the surface, you might be able to carefully grind it down with a grinding wheel.

The Bolt is Still Stuck After Drilling

If you’ve drilled out the majority of the bolt and it’s still jammed, it might be seized in place by rust or thread locker.

What to Do:
- More Penetrating Oil: Apply more penetrating oil and let it soak.
- Heat: Carefully applying heat with a propane torch can help expand the surrounding material, breaking the bond. Be cautious of what is around the bolt.
- Vibration: Sometimes, a sharp tap with a hammer or an impact driver (if you can get it to grip something) can help shock the bolt loose.

Selecting the Right Drill Size for a Bolt

The correct drill size for bolt removal is crucial for using an extractor bolt effectively.

General Rule: The drill bit size should be the minor diameter of the bolt threads, or slightly larger.
Extractor Chart: Most bolt removal tool sets come with a chart that specifies the recommended drill bit size for each extractor. Always refer to this chart.
Example: For a 1/4-inch bolt (which has roughly a 1/4-inch diameter), you’d typically drill a hole around 3/16 inch or 7/32 inch to allow the extractor to bite.

Preventing Stripped Bolts

Prevention is always better than cure. Here are some tips to avoid stripping bolts in the future:

Use the Right Tools: Always use the correct size and type of wrench or socket for the bolt. A 6-point socket offers better grip than a 12-point socket.
Apply Even Pressure: When tightening or loosening bolts, apply steady, even pressure. Avoid jerky movements.
Lubricate Threads: For critical applications or bolts that are prone to seizing, apply a small amount of anti-seize compound to the threads before installation.
Don’t Over-Tighten: Tighten bolts to the manufacturer’s specified torque. Over-tightening is a common cause of stripping.
Inspect Bolts: Before using a bolt, check it for any damage or defects.

Frequently Asked Questions (FAQ)

What is a left-hand drill bit?

A left-hand drill bit is a drill bit that rotates counter-clockwise (to the left). These bits are often used in the process of removing stripped fasteners because their counter-clockwise rotation can sometimes catch the internal threads of a stubborn bolt and unscrew it as you drill.

Can I use a regular drill bit to remove a stripped bolt?

Yes, you can use regular drill bits for metal to drill out a stripped bolt, but you’ll be drilling a hole to insert a separate extractor bolt. A left-hand drill bit offers the added possibility of the bit itself unscrewing the bolt.

What is the best way to remove a completely rounded bolt head?

For a completely rounded bolt head, your best options are to use Vise Grips to grip what’s left of the head, or to use a grinding wheel to cut a new slot for a screwdriver or chisel. If these fail, drilling out the bolt is usually the next step.

How do I know which drill bit size to use for a bolt extractor?

Refer to the size chart that comes with your bolt removal tool or extractor bolt set. This chart will specify the recommended drill size for bolt removal for each extractor size.

Is it safe to use heat on a stripped bolt?

Using heat can be effective, but it must be done with caution. Apply heat only to the surrounding material, not directly to the bolt if possible, to allow for expansion. Be aware of any flammable materials nearby. Always wear appropriate safety gear.

By following these steps and using the right tools, you can successfully drill out most stripped bolts and get your project back on track. Remember, patience and a methodical approach are your greatest allies.