What to Do if a Tap or Drill Breaks in the Hole? Here are Some Practical Solutions to Share with you:
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Apply some lubricant and gently tap the broken surface with a sharp pick or chisel in the reverse direction, occasionally removing the metal filings (this is the most commonly used method in workshops, but may not be suitable for very small threaded holes or long broken taps, though it’s worth trying).
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Weld a handle or a hex nut onto the broken tap’s surface, then gently turn it out (this is a good method, but welding can be a bit troublesome, and it’s not suitable for smaller diameter taps).
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Use a specialized tool: Tap Extractor. The principle is to apply positive and negative electrodes to the workpiece and tap, with an electrolyte in between, causing the workpiece to discharge and corrode the tap. Then, use pliers to remove it. This method causes minimal damage to the inner hole.
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Place a steel roller on the break of the tap and gently tap with a small hammer. The tap, being brittle, will eventually shatter and come out, or more simply, drill out the broken tap’s thread hole and re-tap it (this method is a bit rough and ineffective for small diameter taps, and can be exhausting if the tap diameter is large).
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Weld the threaded hole of the broken tap flat, then grind it smooth and re-drill the hole. Though difficult, it can be done slowly (if the threaded hole can be relocated, it is recommended to drill and tap the hole next to the original one).
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Cut a slot on the broken tap’s surface and use a screwdriver to turn it out in reverse (this slot is difficult to cut, especially for small diameter taps).
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Drill out the broken tap’s thread hole and insert a steel wire thread insert or pin, then weld, grind smooth, and re-drill and tap the hole. This can restore the functionality of the hole (although this method is time-consuming, it is very practical regardless of the tap size).
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Use an electrical pulse to break the tap, either through EDM or wire cutting. If the hole is damaged, it can be reamed and fitted with a steel wire insert (this method is simpler and more convenient, but axis alignment should not be a concern unless the hole’s alignment directly impacts the equipment’s performance).
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Create a simple tool to insert into the chip slot of the broken tap, carefully turning it out in reverse. For example, attach two nuts to a square-ended broken tap, then insert a steel wire (the number of strands matching the number of grooves on the tap) into the gap between the tap and the nuts. Use a wrench to turn the square end in the reverse direction to remove the tap (this method is designed to clear the chip slots, using steel wire or a specialized needle tool. If broken taps occur frequently in the workshop, it is best to make such a tool wrench).
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Nitric acid solution can corrode high-speed steel taps without damaging the workpiece.
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Use an acetylene flame or torch to anneal the tap, then drill with a bit slightly smaller than the base hole diameter. Drill carefully to avoid damaging the thread, then punch with a flat or square punch and unscrew the tap with a wrench.
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Use an air drill to reverse the tap out, relying on feel. The drill doesn’t directly remove the tap but uses slow speed and slight friction (similar to a semi-clutch on a car) to spin the tap out.
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Grind the broken tap surface with a grinder, then start drilling with a small bit and gradually use a larger drill bit. The broken tap will eventually fall off. After it’s removed, use the original-sized tap to re-tap the hole, which avoids increasing the hole size.
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Weld an iron rod onto the broken tap and turn it out (disadvantages: it’s difficult to weld small broken parts; welding skills must be excellent; the welded part may break, and the chances of removing the broken tap are low).
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Pry out the broken part using a cone-shaped tool that is harder than the broken part (disadvantages: only suitable for brittle broken parts, which must be smashed before prying out; it won’t work for parts that are too deep or small, and may damage the original hole).
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Create a hexagonal electrode smaller than the broken part’s diameter, then use an EDM machine to make a hexagonal counterbore on the broken part. Use an Allen wrench to turn it out (disadvantages: ineffective for rusty or stuck parts, unusable for large workpieces, and not suitable for small broken parts; time-consuming and tedious).
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Use an electrode smaller than the broken part’s diameter and use an EDM machine to punch it out (disadvantages: ineffective for large workpieces, which cannot fit on the EDM machine; time-consuming, and when the part is too deep, carbon may accumulate and hinder progress).
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Use a carbide drill bit (disadvantages: may damage the original hole, ineffective for hard broken parts, and carbide drill bits are brittle and may break).
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There is now a portable tool designed using electrical processing principles that can easily and quickly remove broken screws, taps, and drills.
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If the screw is not too hard, you can flatten the end face, find the center point, and use a center punch to make a small dent. Drill with a smaller bit, ensuring the hole is perpendicular, and then use a tap extractor to unscrew it.
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If a tap extractor is unavailable, continue expanding the hole with a larger drill. When the hole diameter nears the screw size, some of the threads may come off, allowing you to remove the remaining threads and re-tap with the same size tap.
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If the broken screw is exposed, or if the broken part doesn’t require high precision, you can saw a slit with a hacksaw, cut through the outer shell, and then use a flathead screwdriver to remove it.
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If the screw extends out to a certain length and the material’s melting point is not too low, you can weld a T-shaped extension onto the screw, making it easy to unscrew using the welded rod.
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If the screw is severely rusted and difficult to handle with the above methods, try heating it with fire, adding a little lubricant, and then apply the relevant method.
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After numerous attempts, even if the screw is removed, the hole may be ruined. In this case, simply drill a larger hole and tap it. If the original screw position and size are restricted, you can use a larger screw, or directly weld the thread and drill a small hole in the center to re-tap. However, when welding, the internal metal structure may cause difficulties when re-tapping.
