While an impact driver can perform some drilling tasks, it's generally not advisable for all types of drilling, primarily due to its design, the specific bits it accepts, and the risk of damaging unsuitable accessories.
The Core Issue: Tool Design vs. Bit Compatibility
An impact driver is engineered differently from a standard drill. A drill provides continuous rotary motion for smooth hole creation. An impact driver, however, combines rotary action with concussive, high-torque blows (percussion) when it encounters resistance. This powerful, intermittent impact mechanism is superb for driving long screws or fasteners into dense materials, but it can be detrimental to drill bits not designed for such forces.
Shank Compatibility: The 1/4″ Hex Limit
Impact drivers are primarily designed to accept accessories with a 1/4″ hex shank. This specialized chuck limits the types of drill bits that can even fit into the tool. While many drill bits now come with hex shanks to allow for quick changes, not all of them are suitable for the unique forces an impact driver exerts.
Risk of Bit Shattering and Damage
The most critical reason you "can't" (or shouldn't) use an impact driver for general drilling is the potential for bit damage and shattering. Even among hex shank drill bits, many, such as certain flat drill bits, are not engineered to withstand the unique, high-torque impact action of these tools. Using such unsuitable bits can lead to them shattering under the stress, posing a significant safety risk and damaging the bit itself. Standard drill bits are designed for continuous rotational torque, not the sudden, percussive jolts of an impact driver, which can cause them to break or warp.
When Drilling with an Impact Driver is Possible (and Recommended)
Despite the limitations, modern tool technology has led to the development of specialized "impact-rated" drill bits. These bits are designed with stronger materials and geometries to withstand the high torque and concussive forces of an impact driver.
You can drill with an impact driver if you use:
- Impact-rated twist bits: Specifically designed for drilling metal or wood.
- Impact-rated spade bits or paddle bits: For larger holes in wood.
- Impact-rated auger bits: For deep holes in wood.
- Impact-rated step bits: For drilling multiple hole sizes in thin materials like sheet metal.
- Self-feed bits: For aggressive drilling in wood.
These bits often feature reinforced shanks and tougher cutting edges to handle the intense forces.
Standard Drill vs. Impact Driver for Drilling Tasks
| Feature | Standard Drill | Impact Driver |
|---|---|---|
| Primary Action | Continuous rotary | Rotary + Concussive impact blows |
| Best For | Precision drilling, versatile hole making | Driving fasteners, drilling in dense materials |
| Bit Types | Wide variety of round and hex shank bits | Primarily 1/4″ hex shank, impact-rated bits only |
| Control | Higher precision, variable speed for control | Less precise for delicate drilling, powerful torque |
| Noise | Relatively quieter | Can be very loud due to impact mechanism |
| Risk of Bit Breakage | Low with correct bit and speed | High with non-impact rated bits |
Practical Considerations and Best Practices
- Choose the Right Bit: Always use impact-rated drill bits when drilling with an impact driver to ensure safety and prevent bit damage.
- Material Matters: Impact drivers excel at drilling through tough materials like concrete (with specific masonry bits) or thick wood, but they are less suited for delicate materials where precision is key.
- Control and Precision: Impact drivers deliver immense torque, which can make fine control difficult, especially when starting a hole or drilling through thinner materials. For precision work, a standard drill is usually superior.
- Noise: Be aware that the impact action can be quite noisy. Always use hearing protection.
In essence, while an impact driver's power is unmatched for driving, its specific mechanism and the compatibility limitations with traditional drill bits mean it's not a universal drilling tool. For general drilling needs, particularly those requiring precision or a wide range of bit sizes, a dedicated drill is the more appropriate and safer choice.
