Drilling a bolt head is a common technique used primarily to remove a damaged, stripped, or seized bolt when conventional methods like wrenches or sockets fail. The process involves drilling through the head to detach it from the bolt's shank, allowing the secured component to be removed. The remaining stud can then often be extracted using other methods.
Why Drill a Bolt Head?
You might need to drill a bolt head in situations where:
- The bolt head is rounded off or damaged.
- The bolt is seized due to rust or corrosion.
- The bolt is broken, leaving a portion of the head attached or inaccessible.
- Impact tools or penetrating oil haven't worked.
Step-by-Step Guide to Drilling a Bolt Head
This process requires patience and precision. Always wear safety glasses.
1. Preparation
- Gather Tools: You'll need a drill (corded or powerful cordless), a set of drill bits (starting small and increasing in size, preferably cobalt bits for strength), a center punch, a hammer, safety glasses, penetrating oil, and potentially a bolt extractor set or vise grips for the remaining stud.
- Clean the Area: Ensure the bolt head and surrounding area are clean of dirt, rust, or debris.
- Apply Penetrating Oil: Spray penetrating oil onto the bolt threads (if accessible) and the base of the bolt head to help loosen it. Let it soak for a while.
2. Center Punch the Bolt Head
- Locate the Center: Find the precise center of the bolt head. This is crucial for accurate drilling.
- Create an Indent: Place the tip of the center punch directly on the center mark. Strike the punch firmly with a hammer to create a small indentation. This indent will guide the drill bit and prevent it from wandering.
3. Start Drilling
- Select a Small Bit: Begin with a small drill bit, significantly smaller than the bolt's shank diameter. This helps ensure accuracy.
- Begin Drilling: Place the tip of the small drill bit into the center-punched indent. Start drilling slowly and apply steady, downward pressure.
- Adjusting Off-Center: As highlighted in the video "PERFECTLY Drill Out A Bolt", if your initial center mark is a little bit off, you may need to slightly adjust your drilling angle as you start to try and steer the bit back towards the true center. This requires a delicate touch early in the process.
- Increase Speed: Once the bit is firmly established in the center and cutting properly, you can increase the drill speed slightly.
4. Increase Drill Bit Size
- Progress Gradually: After drilling partway or all the way through the head with the small bit, switch to a slightly larger bit.
- Repeat: Use each progressively larger bit to deepen or widen the hole started by the smaller bit. Continue increasing the drill bit size until you reach a diameter slightly smaller than the bolt's shank (the part below the head). Drilling too large can damage the surrounding material.
5. Detach the Bolt Head
- Drill Depth: Continue drilling until you've drilled through the entire thickness of the bolt head, reaching the shank or the material the bolt is securing.
- Head Separation: If drilled correctly, the bolt head should eventually detach or become loose enough to pry off with a flathead screwdriver or chisel.
6. Address the Remaining Stud
Once the head is removed, you are left with the bolt's shank (stud) protruding.
- Options for Extraction:
- Bolt Extractors: Drill a smaller hole in the center of the remaining stud and use a spiral screw extractor or a straight-fluted extractor set according to their instructions.
- Vise Grips: If enough of the stud is accessible, grip it tightly with vise grips and try to turn it counter-clockwise to unscrew it.
- Nut & Weld: (Advanced) If accessible, you can sometimes weld a nut onto the end of the stud and then use a wrench on the nut to turn the stud out.
- Drill it Out Completely: As a last resort, you can continue drilling through the entire stud with progressively larger bits until it disintegrates, being very careful not to damage the surrounding threads.
Essential Tools for Drilling Out Bolts
| Tool | Purpose |
|---|---|
| Safety Glasses | Eye protection (crucial!) |
| Drill | To power the drill bits |
| Drill Bit Set | Various sizes, preferably cobalt or titanium |
| Center Punch | To create a starting dimple |
| Hammer | To strike the center punch |
| Penetrating Oil | To help loosen seized threads |
| Bolt Extractor Set | To remove the remaining stud (recommended) |
| Vise Grips | For gripping exposed stud |
Tips and Considerations
- Speed and Pressure: Use a moderate drill speed and steady pressure. Too much pressure can break bits, while too little can cause them to rub and dull.
- Lubrication: For tougher bolts or harder materials, use cutting fluid or oil to lubricate the drill bit and keep it cool.
- Patience: Drilling out a bolt can be time-consuming. Don't rush the process.
- Bit Sharpness: A sharp drill bit cuts more effectively and reduces the risk of wandering or breaking.
- Protect Surroundings: Be mindful of the material around the bolt hole. Avoid drilling into it.
Drilling a bolt head is an effective solution for removing stubborn fasteners, but it requires careful execution to avoid further damage.
