How To Use Left Handed Drill Bits For Stripped Screw Removal And Precision Drilling
Left-handed drill bits operate in reverse counter-clockwise rotation, making them the premier tool for extracting sheared fasteners without damaging surrounding threads. Achieving success requires pairing these reverse-helix bits with a reversible variable-speed drill and precise axial force to catch and back out stubborn material.
Pre-Operation & Equipment Checklist
Extracting broken fasteners and performing precision drilling requires specific preparation to prevent project failure, thread stripping, or bit breakage. Reverse-helix bits (also known as extraction bits) rely on friction and reverse rotation to unseat stuck hardware.
- Essential Gear and Tools: High-speed steel (HSS) or cobalt left-handed drill bits (ranging from 1/16-inch to 1/4-inch), a reversible variable-speed power drill or pneumatic drill, a center punch, a ball-peen hammer, cutting fluid or tapping oil, safety glasses, and extraction screw extractors (as an optional backup).
- Mandatory Prerequisite Knowledge: Understanding of metal hardening, torque limits, pilot hole centering, and drill motor direction switching. Operators must recognize that left-handed bits cut only when the drill chuck rotates counter-clockwise.
- Estimated Budget and Duration Benchmarks: Budget ranges from twenty to sixty dollars for a quality fractional index set. The execution time typically spans five to fifteen minutes per fastener depending on material hardness and depth.
Step-by-Step Reverse Extraction Workflow
Step 1: Secure and Center-Punch the Damaged Fastener
Inspect the broken screw or bolt head. If the fastener is sheared off unevenly or flush with the parent material, file the surface flat using a small metal file to prevent the drill bit from wandering. Place a sharp center punch directly in the exact geometric center of the fastener face. Strike the punch firmly with a ball-peen hammer to create a deep, well-defined dimple. This dimple acts as a mechanical guide for the drill tip, ensuring the bit does not slip and damage adjacent threads or surrounding surfaces.
Step 2: Configure the Reversible Drill Motor
Insert the smallest appropriate left-handed drill bit (typically 1/8-inch for standard medium fasteners) securely into the drill chuck and tighten it completely. Switch your power drill's directional toggle lever to reverse (counter-clockwise rotation). Verify the rotation direction by looking at the drill from the top or front before touching the workpiece.
Warning: Operating a left-handed drill bit in the standard forward (clockwise) direction will immediately dull the cutting edges, generate extreme heat, and potentially snap the bit inside the hole.
Step 3: Apply Cutting Fluid and Initiate Drilling at Low RPM
Apply a few drops of cutting fluid or high-performance tapping oil directly onto the center-punched fastener face. Lubrication reduces friction, prevents premature heat accumulation, and extends the metallurgical life of the bit. Position the drill perpendicular to the workpiece surface. Depress the drill trigger gently to maintain a low RPM (revolutions per minute, roughly 400 to 600 RPM). Apply steady, moderate axial pressure straight down through the drill body. Do not force or rock the drill, as excessive side load causes thin-diameter bits to shatter.
Step 4: Monitor for the Extraction Bite Point
Maintain consistent downward pressure and low-speed counter-clockwise rotation as the left-handed bit bites into the metal. Because the flutes are cut in reverse, the bit is simultaneously drilling into the core of the screw while applying a continuous unscrewing torque to the fastener body. In many instances, the bit will gain enough frictional grip to completely spin the broken screw or bolt backward out of its threaded hole before the drilling depth is even fully achieved.
Step 5: Transition to Larger Bits or Extractors if Necessary
If the initial small left-handed bit drills entirely through the core of the screw without backing it out, switch to the next larger size left-handed bit from your index set. The wider hole thins out the remaining walls of the fastener threads. Often, the increased diameter and higher biting torque of the larger reverse bit will catch the remaining shell and spin it free. If the screw remains completely seized after stepping up in bit size, insert a tapered flute extractor into the clean pilot hole and back it out using a tap wrench.
19 Piece Screw Extractor and Left Hand Drill Bits Set, Easy Out Screw ...
Left-Handed Drill Bit Specifications and Material Matrix
| Parameter / Feature | Standard (Right-Handed) Bits | Left-Handed Extraction Bits | Primary Application |
|---|---|---|---|
| Rotation Direction | Clockwise (Forward) | Counter-Clockwise (Reverse) | Fastener extraction and reverse-torque drilling |
| Flute Geometry | Right-hand helix | Left-hand reverse helix | Channeling chips upward during counter-clockwise spin |
| Material Composition | High-Speed Steel (HSS) / Cobalt | M2/M35 High-Speed Steel with Cobalt | Drilling and extraction in soft metals, steel, and alloys |
| Primary Failure Mode | Dull cutting edges from overheating | Shearing at the shank from side-load pressure | Over-torquing during high-speed extraction attempts |
Common Operational Failures and Field Fixes
- Problem: The left-handed drill bit snaps off flush inside the broken screw shaft.
- Root Cause: Excessive lateral side-loading, too high of an RPM, or using an overly aggressive push force on a small-diameter bit.
- Actionable Fix: Do not attempt to drill through the broken high-speed steel bit with another standard bit, as HSS is exceptionally hard. Use a carbide burr in a rotary tool to grind out the broken fragment, or use a punch and hammer to shatter the brittle steel piece outward.
- Problem: The drill bit wanders across the metal surface and ruins the surrounding material.
- Root Cause: Skipping the center punch step or failing to establish a secure starting dimple.
- Actionable Fix: Stop immediately. Use a small round-nosed metal file to clean up the marred area, create a deeper starter divot with a heavy-duty center punch, and resume drilling at the lowest possible drill speed.
- Problem: The left-handed bit drills a clean hole right through the center of the screw without turning the fastener.
- Root Cause: Severe thread corrosion, thread-locking adhesive (such as high-strength threadlocker), or bottoming out against a blind hole obstruction.
- Actionable Fix: Apply a penetrating catalyst oil and let it sit for thirty minutes. Switch to a larger diameter left-handed bit, or use a dedicated screw extractor paired with a tap wrench to apply higher mechanical unscrewing leverage.
Frequently Asked Questions
Can left-handed drill bits be used in standard forward-rotation drills?
No, left-handed drill bits cannot cut material when the drill is operated in the standard forward clockwise mode. Because their flutes and cutting edges are reversed, they will only scrape and burnish the metal surface. They require a reversible drill motor set to counter-clockwise rotation to function correctly.
Do left-handed drill bits work on hardened steel bolts?
Standard high-speed steel left-handed bits struggle with heavily hardened grade 8 or stainless steel bolts. For high-tensile fasteners, you must use cobalt-alloyed left-handed bits combined with continuous cutting fluid application and very low drill motor speeds to prevent work hardening.
Will a left-handed bit damage the internal threads of a tapped hole?
When used correctly in the proper size, left-handed bits target the solid core of the broken fastener. Because they pull the fastener inward and outward simultaneously, they generally preserve the original tapped threads of the parent material much better than traditional easy-outs that expand the screw outward.
Can left-handed bits be sharpened?
Yes, left-handed drill bits can be re-sharpened using a specialized drill bit sharpening jig or a bench grinder equipped with a fine aluminum oxide wheel. However, due to the reverse helix angle, the relief angles and chisel edges must be ground with opposite orientation compared to standard right-handed bits.
Master the art of fastener extraction and precision drilling by equipping your workshop with a professional-grade set of left-handed drill bits today.
