To remove a damaged bolt, center-punch, drill a pilot hole, use a left-hand bit or extractor, then repair threads if needed.
Stuck fasteners waste time and can stall a repair. This guide shows a clean, methodical way to do the job with standard tools, safe practices, and clear checkpoints. You’ll see where heat helps, where patience pays off, and when to switch from extraction to thread repair.
What You’ll Need And Why It Matters
Gather the right kit before you touch the workpiece. A steady setup prevents broken bits and saved holes. Here’s a compact list that covers most situations.
- Center punch and hammer
- Cobalt or HSS-cobalt drill bits (including left-hand bits)
- Screw/bolt extractor set (spiral or straight-flute)
- Variable-speed drill or drill press
- Cutting fluid or light oil
- Penetrant (e.g., penetrating oil)
- Heat source (small torch or heat gun) when threadlocker or corrosion is present
- Drill guide block or bushing, if available
- T-handle tap wrench, taps, and thread repair kit (Helicoil or solid bushing insert)
- PPE: ANSI Z87.1-rated safety glasses, gloves suited to sharp metal, hearing protection
Bit Choices, Uses, And Notes
This quick table helps you pick a cutting tool that matches the metal and the task. Start with a sharp pilot bit and keep speeds under control to avoid work-hardening.
| Bit Type | Best Use | Notes |
|---|---|---|
| HSS-Cobalt (M35/M42) | Hardened bolts, stainless, alloy steel | Holds edge at heat; run slower RPM with cutting oil. |
| Left-Hand Twist | Back-spinning a snapped shank during drilling | Often frees the stud while drilling the pilot hole. |
| Titanium-Coated HSS | Mild steel, aluminum, brass | Good general use; coating reduces friction. |
| Carbide (Solid) | Work-hardened spots or hardened tool steel | Fragile; use rigid setup and true alignment only. |
| Step Bit | Thin sheet around captive nuts | Controls hole growth; avoid on thick sections. |
Safety And Setup Come First
Clamp the work so nothing shifts. Wear eye protection with side shields; flying chips are common in this task. Guidance for eye and face protection appears in OSHA’s 1910.133 standard, which calls for impact-rated gear during drilling and similar work. Keep sleeves tight, tie back long hair, and keep a tidy bench so the drill cord or hose doesn’t snag.
Signs Extraction Will Go Smoothly
Some stuck fasteners come out with minimal drama. You’re in the easy zone when the shank broke above the surface, corrosion looks light, or the fastener was installed with medium-strength threadlocker. Where a permanent threadlocker cured on the threads, a little heat breaks the bond first; Henkel explains that red threadlocker softens with localized heat around 250 °C (about 550 °F). See their note on removing red grades on Henkel’s threadlocker guidance.
Drilling Out A Bolt Safely: Step-By-Step
Follow this exact sequence. Each step builds accuracy and keeps the hole centered on the shank.
1) Soak, Mark, And Square The Work
Apply penetrant and give it a few minutes to wick in. Clean the top of the broken shank with a file or a flat wheel so your punch can’t skate. Use a center punch to mark dead center; tap once to place, then a second, firmer strike for a crisp dimple. Check from two angles. If the mark drifts, re-face the top and punch again.
2) Guide The Pilot Hole
Choose a pilot bit around 1.5–3.0 mm (1/16–1/8 in.) depending on shank size. If you have a drill guide block or a bushing, set it square over the punch mark. A guide stops wandering and keeps the bit perpendicular. Start at low speed with light feed. Let the bit cut; don’t force it.
3) Try A Left-Hand Pilot First
Swap to a left-hand pilot in the same size. Run the drill in reverse. Many times the bit bites and backs the shank out while you’re still in the pilot stage. If the shank begins to twist free, keep the feed steady and let it unwind. If nothing moves, keep building the pilot hole to the required extractor size.
4) Step Up To The Extractor Size
Extractor sets specify a pilot size for each extractor. Drill to that size in small steps, keeping the hole straight and centered. Brush chips often and feed oil when cutting steel. If the hole grows slightly off-center, stop and reset your guide; drifting weakens the parent threads.
5) Set The Extractor
Blow out chips. Tap the extractor gently into the hole. For spiral extractors, seat it deep enough for full engagement. Use a T-handle for torque control. Turn counterclockwise with smooth pressure. If the extractor slips, reset it. If it squeals or feels springy, back off; forcing it can snap the extractor, which is hardened and tough to drill.
6) Use Heat When Adhesives Or Rust Fight Back
Warm the area around the fastener, not the bit or extractor. A small torch aimed at the boss or flange helps release threadlocker and expands the parent metal. Move the heat in short bursts and give time for capillary penetrant to work again. Try the T-handle once more with steady, even torque.
7) Commit To Drill-Through If The Shank Won’t Turn
If extraction stalls, your next move is a clean drill-through. Enlarge the hole until only a thin ring of threads remains on the stuck shank. Pick out the residue with a scriber or a small punch. Run a tap of the original size through the bore to chase remaining material. If the threads are too damaged, plan for an insert or an oversize repair.
RPM, Feed, And Cooling Tips
Heat kills edges and hardens steel locally. Keep speed low on tough bolts and add oil. For thicker sections or stainless, lower RPM and feed with firm, steady pressure. A light peck cycle helps clear chips. If you see blue chips or the bit squeaks, pause and cool the cut. A pilot hole reduces load and helps the full-size bit track true.
Helicoil, Solid Inserts, And Oversize Options
Thread repair comes in two flavors: coil inserts and solid bushings. Coil inserts restore the original bolt size with a stainless spring that matches the pitch. Solid bushings (Timesert-type) add wall thickness and excel in soft alloys. Choose based on remaining parent material and access for drilling a larger tap hole. Keep the drill square, tap carefully with cutting fluid, and seat the insert flush or slightly below the surface. Mark the repaired hole so the next tech knows an insert lives there.
Extractor Styles And When To Use Them
Two patterns dominate most kits. Each has a sweet spot.
Spiral (Tapered)
Bites quickly and suits shallow holes. Needs a stouter wall of material around the pilot because it wedges as it turns. Great for mid-size shanks where access is decent.
Straight-Flute
Applies torque without as much radial wedging. Better for small bolts, deep holes, or when the parent threads are thin. Often used with a matching drill bushing for alignment.
Common Mistakes And Easy Fixes
- Off-center pilot: Re-face the shank top, re-punch, and restart with a guide block.
- Work-hardened spot: Switch to a fresh cobalt bit, lower RPM, add oil, and use firmer feed.
- Snapped extractor: Carbide will cut it, but only with rigid setup. If you can’t hold alignment, take it to a drill press or machine shop.
- Threadlocker fighting you: Warm the boss, not the bit. Try the T-handle again while the metal is still warm.
- Burrs at the entry: Deburr with a light countersink so the tap starts straight.
Sizing Primer: From Bolt To Pilot And Tap
Picking the right pilot prevents wall damage and keeps extractors alive. Use the extractor maker’s chart when possible. If you don’t have the booklet, the table below gives practical ranges that work with common kits. Measure your bolt’s nominal size, then match a pilot that suits your extractor.
| Bolt Size (Coarse) | Typical Pilot Range | Tap For Repair |
|---|---|---|
| 1/4-20 (M6 x 1) | 2.5–3.5 mm (3/32–9/64 in.) | Original: 1/4-20 or M6 x 1; insert kits available |
| 5/16-18 (M8 x 1.25) | 3.5–4.5 mm (9/64–11/64 in.) | Original: 5/16-18 or M8 x 1.25; insert kits available |
| 3/8-16 (M10 x 1.5) | 4.5–5.5 mm (11/64–7/32 in.) | Original: 3/8-16 or M10 x 1.5; insert kits available |
| 7/16-14 (M12 x 1.75) | 5.5–6.5 mm (7/32–1/4 in.) | Original: 7/16-14 or M12 x 1.75; insert kits available |
| 1/2-13 (M14 x 2) | 6.5–8.0 mm (1/4–5/16 in.) | Original: 1/2-13 or M14 x 2; insert kits available |
Left-Hand Bits: Why They Work So Well
These bits cut while the chuck spins in reverse. The cutting forces nudge the shank in the loosening direction. With a square punch, a pilot that stays centered, and low RPM, a left-hand pilot often saves the day before you ever touch an extractor. Keep a dedicated set in the box so you’re not tempted to skip this step.
When Heat Is Your Friend
Heat breaks bond lines. On threadlocked joints, target the parent part around the bore, warm it evenly, and avoid open fuel or wiring nearby. Back away from paint and seals that can scorch or melt. After warming, try a quarter-turn on the T-handle. If it gives, work it back and forth and add fresh penetrant as the joint cools.
Protecting The Parent Threads
The hole you’re saving matters more than the broken shank. Keep alignment square. Use a bushing or a guide where space allows. Step drills in small jumps. Stop when chips turn blue or the feed feels crunchy. Reset, cool the cut, and continue only when the bit runs smooth again. Your tap and insert will thank you later.
Decision Tree: Which Path To Take
If The Shank Protrudes
Start with penetrant. Try small locking pliers with steady torque. If it moves a hair, work it back and forth. If it doesn’t move, file the tip flat, punch center, and go to the pilot stage.
If The Shank Is Flush Or Below The Surface
Go straight to the punch and pilot. A short drill bushing helps a lot here. Build the hole in steps until your extractor size fits. Don’t chase the last bit of metal at the wall; save those threads by switching to a tap and cleanout.
If The Shank Sits In Soft Aluminum
Keep RPM down and use plenty of oil. Aluminum loads flutes fast; clear chips often. If the hole grows off-center, plan for an insert. Solid bushings hold up well in cast housings.
If The Fastener Used Permanent Threadlocker
Add gentle heat first. Then try the extractor while the area is still warm. Henkel’s guidance on high-strength grades gives a temperature target, linked earlier in this guide.
Care, Storage, And Bit Life
Hold back a small budget for sharp cutters. Retire bits that burnish instead of cutting. Keep extractors clean and dry. A light coat of oil on steel tools slows rust. Label the case with the pilot sizes that pair to each extractor; that tiny note saves time every time you open the kit.
Proof You Worked Methodically
When the job is done, take a quick photo of the punched mark, the pilot, and the final cleaned threads. Small receipts like that boost trust with customers and teammates and help you track which steps saved time on the next seized fastener.
Quick Reference Checklist
- Clamp, PPE, tidy bench.
- File the shank top flat and center-punch.
- Pilot at low RPM with oil; use a guide block.
- Try a left-hand pilot in reverse.
- Step up to the extractor size; seat the extractor.
- Warm the parent part if corrosion or adhesives resist.
- Drill-through and chase with a tap if extraction fails.
- Install a coil or solid insert if threads are damaged.
When To Hand It To A Machine Shop
Two red flags call for a rigid setup: a snapped extractor in the hole, or critical bores where alignment must be dead-true. A shop can EDM or mill out hardened pieces and restore threads on center. That cost is cheaper than replacing a housing or a head.
FAQ-Free Final Notes
This method avoids guesswork. Start with a precise punch, guide a small pilot, lean on left-hand cutters, and only then reach for an extractor. If the shank won’t budge, a clean drill-through plus a proper thread repair gives a lasting fix that looks like it came that way from the factory. Stay patient, keep bits sharp, and protect the parent threads every step of the way.