How To Use Left Handed Drill Bits: The Complete Extraction Guide
Left-handed drill bits—also known as reverse drill bits—rotate counterclockwise to back out sheared-off fasteners while drilling forward, making them the ultimate tool for effortless broken bolt extraction. Mastering this specialized procedure requires reversing your drill's motor, applying consistent low-RPM axial pressure, and pairing the bit with a reliable screw extractor set.
Essential Preparation and Tool Selection for Reverse Drilling
Executing a successful extraction operation relies on preparing the correct hardware and understanding the metallurgical properties of the fasteners you are targeting. Unlike standard twist drills that cut clockwise, left-handed drill bits are engineered with reverse spiral flutes made from High-Speed Steel (HSS) or Cobalt (M35 or M42). These materials allow the cutting edge to bite into grade-8 bolts, stainless steel studs, and hardened carbon steel without shattering under high torque.
Before approaching the broken fastener, gather your workshop assets and verify your workspace setup.
- Essential Equipment and Hardware: Left-handed drill bit set (typically ranging from 1/16 inch to 1/2 inch), a variable-speed reversible drill or impact driver, center punch, ball-peen hammer, cutting fluid or tapping oil, safety glasses, and a wire brush.
- Prerequisite Knowledge & Safety Standards: Wear ANSI-approved eye protection, as hardened metal shards shear off at high velocities. Ensure your power drill features a functional reversing switch capable of high-torque output at low rotational speeds.
- Time and Budget Benchmarks: A standard extraction takes approximately 10 to 30 minutes per bolt. Basic cobalt bit sets range from thirty to sixty dollars, while professional-grade extraction kits run upwards of one hundred dollars.
Step-by-Step Execution Workflow for Removing Broken Fasteners
Step 1: Clean and Prepare the Broken Bolt Face
Examine the broken fastener to determine if the fracture surface is jagged or recessed below the surrounding metal surface. Use a wire brush and compressed air to strip away rust, carbon buildup, and grease from the broken stud face and surrounding threads. Apply a penetrant spray such as PB Blaster or Kroil directly to the threads, allowing it to soak for at least fifteen minutes to loosen corrosion before you begin drilling.
Step 2: Center Punch the Fastener
Accuracy dictates the success of your extraction. Place a sharp center punch directly in the exact mechanical center of the broken bolt face. Strike the top of the punch firmly with a ball-peen hammer to create a deep, well-defined dimple.
Warning: Off-center drilling will cause the bit to wander into the softer surrounding base material, ruining the threads of your engine block, machinery casing, or structural frame.
Step 3: Configure the Drill and Select the Bit Size
Select a left-handed drill bit that measures approximately one-third to one-half the total diameter of the broken bolt. Insert the bit firmly into your drill chuck and tighten it securely. Switch your power drill into reverse mode (counterclockwise rotation). Verify the spin direction by looking at the drill from the top; the chuck must rotate from right to left toward you.
Step 4: Drill at Low RPMs with Cutting Fluid
Apply a generous drop of cutting fluid to the center punch dimple to manage frictional heat and maintain the temper of the cutting edge. Place the tip of the left-handed bit into the dimple, maintain a firm, straight axial load, and squeeze the trigger. Run the drill at a slow, controlled speed—ideally between 400 and 600 RPM. High speeds generate excessive heat that dulls the bit and work-hardens the steel fastener.
Step 5: Back Out the Fastener
As the reverse flutes bite into the metal, the counterclockwise rotation creates upward and outward shearing forces. In many cases, the friction generated by the drilling process combined with the reverse bite will cause the entire broken bolt to unthread and spin out of the hole before you finish drilling all the way through. If the bolt does not spin out on its own, continue drilling deep enough to accept a screw extractor or rely on the bit to completely core out the center of the stud.
Best left handed drill bits: top picks for efficiency and precision
Left-Handed Drill Bits vs. Standard Bits and Extractors
| Feature | Left-Handed Drill Bits | Standard Drill Bits | Traditional Screw Extractors (Easy-Outs) |
|---|---|---|---|
| Rotation Direction | Counterclockwise (Reverse) | Clockwise (Forward) | Counterclockwise (Reverse) |
| Primary Function | Drilling holes and extracting broken fasteners simultaneously | General-purpose material penetration | Removing fasteners via pre-drilled pilot holes |
| Risk of Wedging | Low; cuts and backs out material | High; tightens broken threaded studs deeper | Very High; prone to snapping inside the hole |
| Material Composition | High-Speed Steel (HSS) or Cobalt | Carbon Steel or HSS | Hardened Tool Steel |
Common Operational Failures and Field Remedies
- Root Cause: The drill bit snaps off inside the broken bolt hole due to excessive lateral pressure or high RPMs.
- Actionable Fix: Because the bit is made of hardened cobalt, standard drill bits will bounce off it. Use a carbide burr in a rotary tool to grind out the broken piece, or use a pointed punch to shatter the remnant, then vacuum out the fragments.
- Root Cause: The left-handed bit slips and strips the center punch mark without cutting into the fastener.
- Actionable Fix: Re-evaluate your center punch depth. Switch to a smaller pilot bit (such as a 1/8-inch left-handed bit) to establish a pilot hole before stepping up to a larger diameter.
- Root Cause: The drill motor stalls under pressure or the chuck slips on the drill bit shank.
- Actionable Fix: Ensure your drill is set to low gear (if equipped with a mechanical two-speed transmission) to maximize torque delivery. Tighten the keyless or keyed chuck firmly, and clear any metal shavings clogging the bit flutes.
Frequently Asked Questions
Can you use left-handed drill bits in a standard forward-spinning drill?
No. Left-handed drill bits are engineered with reverse spiral flutes that only cut when rotated counterclockwise. Operating them in a standard forward-spinning drill will cause the non-cutting edge to rub against the material, generating extreme heat and instantly dulling the tool.
Will a left-handed drill bit remove every broken bolt?
They successfully remove a high percentage of broken fasteners, particularly when the bolt has sheared due to over-torque or fatigue rather than severe rusting. If a bolt is chemically fused or cross-threaded into the base material, you may need to drill out the core completely and chase the threads with a tap.
Do I need a special drill to use reverse bits?
You do not need a specialized drill, but your power tool must feature a variable-speed trigger and a functional reversing switch. Cordless hammer drills, standard driver-drills, and reversible pneumatic drills all support left-handed drilling operations.
What is the advantage of a left-handed bit over an Easy-Out extractor?
Traditional tapered extractors expand the diameter of the broken bolt as you drive them into the pilot hole, wedging the threads tighter against the parent material and frequently snapping off. Left-handed drill bits remove material and apply loosening torque simultaneously without wedging the fastener.
Upgrade your workshop capabilities today by adding a professional cobalt left-handed drill bit set to your toolbox and eliminate broken fastener headaches forever.
