How to Remove a Broken Tap (and Stop Breaking Them)

Quick answer: Stop turning, clear the chips, and look at how the tap broke before you touch it. If it snapped cleanly at or above the surface, try a tap extractor first. If it is flush, shattered, or deep, the reliable fix is EDM. If the part is aluminum and the tap is steel, an alum soak can dissolve the tap. Do not drill it with an HSS bit: the tap is harder than the drill. If the part is cheap or the hole is already damaged, re-drill for the next size up or a thread insert instead.

A broken tap is one of the most frustrating moments in the shop. The good news is that most broken taps are preventable, and most stuck ones can be removed without scrapping the part if you pick the right method.

Why taps break

Taps are hard and brittle. They resist wear well but snap rather than bend when overloaded. Common causes, summarized from AIMS Industrial’s broken tap guide and general tap maker guidance:

• Hole too small. More thread percent means much more torque. A 1/4-20 tapped into a #8 hole (0.199 in) is about 78.5% thread; the standard #7 (0.201 in) is 75.4%. Go smaller and the torque climbs fast.
• Chips packed in a blind hole. A straight-flute or spiral-point tap can push chips to the bottom until the tap jams and shears.
• Bottoming out. The tap hits the bottom of a hole that was not drilled deep enough, and you keep turning.
• No cutting fluid, especially in stainless and aluminum, where chips weld to the tap.
• Misalignment or side load, such as a hand tap started crooked.
• Forcing through resistance instead of backing off to break and clear chips.

How to prevent it

• Use the right drill, and consider a slightly larger one. Guhring recommends 60% to 70% thread for most work and notes that 100% thread is only about 5% stronger than 75% but takes about three times the torque (Guhring). For 1/4-20 in tough material, our charts list a #3 (0.213 in, 57%). See percent of thread.
• Drill blind holes deeper than the thread. AIMS suggests at least three pitches deeper than the tapped depth. Our blind hole tap depth guide covers this in detail.
• Match the tap to the hole. Spiral-point (gun) taps push chips ahead and suit through holes. Spiral-flute taps lift chips out and suit blind holes.
• Use cutting fluid suited to the material, and back off to break chips when hand tapping.
• Consider a form tap in ductile materials. It makes no chips to pack. See cut vs form tapping.
• Know your material. Stainless work-hardens and grabs; aluminum welds to the tap if dry.

Step 1: Assess before you act

AIMS puts it bluntly: two minutes of assessment can save hours. Ask:

Blow out the chips first. Some machinists also soak the area with penetrating oil before trying anything mechanical; AIMS suggests 10 to 15 minutes.

Method 1: Tap extractor

A tap extractor has hardened steel fingers that slide down into the tap’s flutes. Walton, which has made them since 1908, describes three steps (Walton instructions):

1. Remove all chips. Push the fingers gently but firmly into the flutes.
2. Push the holder down to the tap and slide the sleeve down to the work.
3. Put a tap wrench on the square end, twist forward and back a few times to loosen it, then back the tap out.

Extractors are sold to fit specific tap sizes, so match yours to the broken tap. They work best when the tap broke cleanly, is near flush or above, and still has a little play. If it does not move under light force, stop. The fingers are hardened and brittle; break one off in the hole and you now have two problems.

Method 2: Left-hand drill (only with care)

A left-hand (reverse-spiral) drill turns counterclockwise. On a tap that is loose but not seized, the drill’s bite can sometimes spin the tap out before it cuts much. AIMS treats this as a quick first try on larger taps with some protrusion, using a drill smaller than the tap’s core. Remember that an HSS drill will not cut a hardened tap, so if nothing happens in the first few turns, stop before you damage the surrounding threads.

Method 3: Carbide end mill or carbide drill

Solid carbide is harder than HSS and can cut a tap. This is a machine job, not a hand-drill job. Rigidly fix the part on a mill or a solid drill press, center precisely on the tap, use a carbide tool smaller than the tap’s core diameter, and take light cuts with plenty of fluid. Once the core is gone, the thin flute pieces can often be picked out. The risk is wandering into the threads if you are off-center, so on a critical part, EDM is the safer choice.

Method 4: Alum dissolving (steel taps in aluminum parts only)

This is an old machinist’s trick and it works. Potassium alum dissolved in hot water slowly eats a steel tap while leaving aluminum largely unharmed.

• Use a glass, ceramic or plastic container, not a steel pot.
• Dissolve as much alum as the hot water will take, submerge the part, and keep it warm, just below simmering.
• Wait. AIMS reports roughly 2 to 8 hours, or overnight for larger taps. Times vary with tap size, depth and temperature, so check on it periodically.
• Rinse, pick out the residue, and chase the thread with a tap.

The alum method does not work on steel, stainless or cast iron parts, because the solution attacks the part too. If the finish matters, try it on scrap first. AIMS also mentions sodium bisulfate (sold as pool “pH down”) as an alternative.

Method 5: EDM

Electrical discharge machining erodes the tap with sparks instead of force. It works on flush, deep and shattered taps, in any electrically conductive material: steel, stainless, aluminum, titanium and more. It does not work in plastics or composites. Many machine shops offer EDM tap removal as a service, and portable tap-burning units exist for shops that need them often. For a valuable part, this is usually the right call.

When to give up and re-drill

Sometimes extraction costs more than it saves. Re-drill when:

• The part is cheap or easy to remake.
• Extraction attempts have already damaged the threads.
• You are allowed to change the thread size.

Option A: Go up a size. Once the tap is out (or the area is cleaned up by EDM or carbide), re-drill and tap the next size. A failed 1/4-20 can become a 5/16-18 with an F drill (0.257 in). A failed M6 can become an M8 with a 6.8 mm drill. Check that the mating part’s clearance hole can be opened up too.

Option B: Thread insert. A helical wire insert or solid bushing restores the original thread size in an oversize hole. Follow the insert kit’s own drill and tap sizes, not a standard tap drill chart, because the tap in a repair kit is special to that insert. Inserts are especially useful in soft materials like aluminum.

Bottom line

Assess first, never force it, and match the method to the break and the material: extractor for a clean break, alum for steel in aluminum, EDM for everything difficult. Then fix the cause so it does not happen again. The easiest win is usually a correct, or slightly larger, tap drill from the UNC, UNF or metric chart.