A Detailed Overview of How to Remove A Broken Tap - Zintilon

Threaded joints are a standard feature during part fabrication, especially when manufacturing large structures that require assembling. They allow the fastening of different parts and components to create a more sophisticated one.

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That said, tapping is the go-to method for creating internal threads required for this application. However, these taps are fragile and may break, especially after exerting force during threading. Therefore, understanding how to remove a broken tap is essential.

This article explores tap machining, focusing on the reasons for tap breaks and practical approaches on how to remove a broken tap from your workpiece. Let’s get right into it. 

What is Tap Machining?

Tap machining is a manufacturing process for creating internal workpiece threads. The technique uses a specialized tool – a tap – for this purpose. The tap is a cutting tool with threads, which makes it suitable for creating the intended thread patterns by removing pieces of material from the hole in the shape of the intended thread.

The machinist rotates the tap into a pre-drilled hole to create the threads into the workpiece. This technique offers applications in assembling and fastening various parts in various industries.

Tap machining is pretty straightforward, making it a popular choice for manufacturing internal threads of various sizes. A typical tap is a simple tool with grooves along the axial direction, allowing easy chipping off workpiece pieces during the procedure.

Potential Reasons Why Tap Break

Several reasons may result in broken taps, each altering the output of the manufacturing process. Below, we explore some of the potential causes of a broken tap. Let’s get into them.  

Low Tap Quality

The quality of the tap’s material is one of the leading factors. Taps manufactured from substandard material have a high risk of breakage, especially after exposure to machining stress. Therefore, it is crucial to use taps manufactured from appropriate materials. Also, go for taps that process like heat treatments have hardened so you do not experience breakage during machining or creating internal threads.

Excessive Tap Wear and Tear

Poor maintenance practices are another potential risk factor for tap breakage. Always check through the taps, especially the cutting edges, before using them to ensure they are in optimum condition. If you notice signs of damage, you should replace them to avoid tap breaking during machining.

Poor Tap Selection 

When selecting tap to create internal threading, choose one of the correct sizes and material types that suit the workpiece. Basic properties such as the tap size and other mechanical features require consideration when selecting the tap. Wrong tap choice will lead to excess stress, which may affect the tap’s integrity, resulting in breakage.

An incompatibility between the tap’s material and the workpiece may also increase the risk of tap breakage. For example, creating internal threads in a hardened steel or titanium workpiece with an aluminum tap is not a good idea. While aluminum has good mechanical properties, it is not strong enough and may require you to exert more force to achieve the tapering. However, it is likely for the tap to break during such tapping.

Unreasonable Cutting Speed and Feed Rates

The machining parameters are also important, especially the cutting speed and feed rates. Overly high cutting speed will cause increased vibration, heat build-up, contact forces and stress, altering the tap’s integrity. Therefore, the machinist must optimize the tap’s feed rates to achieve desirable outcomes without breakage.

Error in Axial Synchrony

Another potential reason for tap breakage is misalignment. This occurs when you apply force to the tap’s grooves and tapering in the wrong axial direction. Performing tap machining in wrong synchrony will cause uneven force distribution and increased stress, especially in the thinner areas of the tap, causing damage.

Low Quality of Lubricating Oil and Cutting Fluid 

Optimum lubrication is an integral part of any machining, as it helps to reduce friction and heat build-up. Therefore, using low-grade lubricating oil and cutting fluid will cause increased friction, stress and heat, straining the taps and causing breakage.

Overly Small Bottom Hole

An insufficient hole size will exert pressure and increase stress on the tap, causing it to break. The tap experiences an increased strain, which, if not optimized, results in straining the material beyond its limit.

Difficulty in Chip Breaking or Removal

Besides an overly small hole, if it is too deep, it makes tapping challenging, leading to chip breaking and accumulation, causing increased stress and potential breakage. Also, when the hole is too deep, it may make removing the tap after creating the taper challenging, contributing to tap breakage.

How to Remove Broken Taps: Practical Methods

Even with a proper understanding of how tap breaks during machining, it is almost inevitable to experience them at one time or another. Therefore, it is important that you understand how to remove broken taps in your fabrication. Below are practical approaches to effectively remove broken taps.

Manual Removal

As the name suggests, this involves using a mechanical tool such as a hammer or a pliers to tap out the broken tap, applying shear force. The process is straightforward, but you must be careful even as you hammer out the broken tap. You might need to use a smaller tool to direct your force as you hammer the tap out of the hole. You use the pliers to pull it out. 

However, this is a crude method, stressful and time-consuming. Therefore, it is not the best choice. Moreover, it is risky because as you attempt to hit the tap, you may also hit or even damage more critical components of the workpiece. 

Chiseling

Another mechanical tool that suits the removal of broken taps is a chisel. However, it is ideal for only cases with partial exposure to the tap. You can use the chisel to carefully break off pieces of a tiny slot at the threaded hole. Afterward, you can use a screwdriver to pull out the remainder of the tap.

Application of Appropriate Lubricating Oil

One of the causes of a broken tap is poor lubrication. Therefore, applying appropriate lubricating oil and cutting fluid will prove effective for removing and even preventing broken taps. It’s pretty straightforward and typical in many machine shops because of its effectiveness. You lubricate the hole, then attempt to push the broken tap in the reverse direction. The oil penetrates and loses the tap, allowing easy extraction.

Tap Extractors

As the name suggests, these are tools specific for removing broken taps. Since tap breaking is almost inevitable, tap extractors are standard for machining shops. It consists of a simple cylinder with three or more claws that enable easy picking and removal of the broken tap pieces without damaging the original workpiece.

Drilling 

Another simple yet effective method of removing broken taps is through drilling. This technique involves using a drill bit to create a hoke of similar diameter in the affected area. It is expected that the drill should push out the pieces of the tap left. However, you might need to use an extractor to ensure complete tap removal.

Using a Pneumatic Drill

The pneumatic drill is another tool that allows easy removal of broken taps. Configure the drill to a low setting before hitting the tap. As the air or pneumatic drill rotates, it loosens the broken tap inside the hole, permitting easy removal.

EDM Machining

EDM machining is one of the most reliable and safe methods of removing broken tap pieces in your workpiece. The EDM machine can erode central pieces of the fractured tap stuck in your workpiece, leaving the cutting edges with the internal threads without any significant defect. 

The machine uses the electric discharge to knock out the tap pieces, and the tap remains in your workpiece. However, you can also push out the broken tap pieces with the machine’s electrode. But when deciding to use EDM for tap removal, ensure that your machine shop has enough room to accommodate the device. 

Also, we must inform you that this process has its limitations, as it is best suited for more robust machine parts and may retain carbon deposition on your part, needing more surface finishing.

Welding

Welding may also help in removing a broken tap. You can weld a handle or a hex nut at the broken gal position, then use an extractor such as a wrench to remove the tap. This method is also simple, but you should only engage if you are sure of your welding expertise. 

Grinding

Precision grinding also benefits broken tap removal. First, grind the broken tap to flatten it, then use a drill to increase the width of the hole. Afterward, carefully increase the hole size; sooner or later, the top will fall off. Just ensure that you follow the procedure carefully to prevent altering the workpiece functionality.

Application of Corrosive Chemicals 

This simply refers to using appropriate chemicals capable of crossing the tap. A typical example of such a chemical is nitric acid. Carefully pour the chemical around the workpiece. However, you need to be sure it will not damage the workpiece. 

Manufacturing Tips to Prevent Tap Breakage

While breaking of tap during tap machining is a likely occurrence, there are expert tips that may prove effective for creating the internal threads without breakage or damage. Let’s delve into the common ones.

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Don’t Force the Rotation 

During tap machining, don’t force the rotation of the tap. In fact, when you notice any difficulty, you should lubricate the tap to enhance the rotation. Forceful rotation of the taps is a recipe for machining defects, such as breakage.

Maintain Stable Force During Tapping 

Maintaining a stable force during tapping is another tip to prevent breakage. Applying uneven force during tapping may stress the tap, cause misalignment, or even alter the synchrony of the rotating tap. Therefore, ensuring a stable force may prove vital for avoiding tap breakage.

Align Tap with Tap Hole

Remember that misalignment is a cause for tap breakage. Therefore, ensuring proper tap alignment to the eye hole is critical for preventing breakage and eventual damage. If the tap is properly aligned to the hole, and you apply the force along the axial direction of the taper, tapping will be a lot easier. The tap will experience less stress, reducing the chances of deformation and breakage.

Position Tapping Length on the Tapping Tool

Ensure that the tapping length is set directly on the tapping tool during tapping. This allows you to prevent overloading the tap, such as exceeding the recommended depth or fluctuating the tapping force, resulting in breakage. Moreover, wrong positioning may cause the tapping drill to penetrate the hole, breaking the tap or even creating an excess hole in the workpiece, altering the product’s functionality.

Use Appropriate-sized Spanner During Tapping

Use appropriate tapping tools, such as the right-sized spanner to provide the required torque to drive in the tap, creating the intended threads. Using an inappropriate spanner will create an uneven force, causing tap misalignment and eventual breakage.

Carefully Take Out Taps

Exercise caution when removing the tap after creating the desired internal threads in your workpiece. Exerting force, such as rushing the tap extraction process, may cause damage. After making the internal thread in your workpiece, you should take your time as you attempt to remove the tap to prevent breakage.

Zintilon: Your Partner for High-Quality CNC Machining Services 

We already reiterate how common the occurrence of tap breaking is. However, beyond understanding how to remove the broken tap from your fabrication, it’s best to consult with an expert partner to guarantee a successful project. 

Zintilon is an expert CNC machining service provider. Our services cut across milling, drilling, turning, tapping, sheet metal fabrication, prototyping and other related technologies. We boast expert machinists who are knowledgeable on how best to achieve your manufacturing goals. Moreover, all our services are industry-standard and at competitive pricing. 

Don’t hesitate to contact us today!

Conclusion

This article emphasizes the importance of taps in manufacturing, especially in fastening and part assembly. However, these taps are fragile and tend to break, even when maintaining extra care during machining. Consequently, we discuss different practical methods to remove a broken tap from your part. Just ensure that you select the one that best suits your fabrication requirements and that the part retains its structural integrity. 

FAQs

Why Do You Need to Remove Broken Taps?

Tapping is a routine manufacturing process that helps create internal threads. However, broken taps disrupt the process, preventing successful fabrication. Therefore, you must remove these taps. Below are reasons you need to rid your workpiece of broken taps.

What Kind of Drill Bit Do You Need to Drill Out a Broken Tap?

When using a drill to remove broken taps, use a solid carbide or cobalt drill bit. They are capable of drilling into hard, rigid, and challenging materials. 

What Tool is Used to Remove a Broken Tap?

While there are many tools, including a drill bit, hammer, chisel, etc., and methods to remove broken taps. However, a tap extractor is explicitly designed for this purpose. It is equipped with claws that help ensure the extraction of the fractured tap pieces.

The answer is yes, however, there are several issues to consider to avoid liability. For this discussion, we will assume a requirement for threaded rebar as follows:

#8 x 48″ long A615 grade 60 rebar with 8″ thread one end.

What is rebar?

Rebar is short for “reinforcing bar” and often used in concrete foundations to strengthen the concrete. It is held in place by systematic ridges or deformations in its surface that allow the concrete to “grip” the bar better than plain round bar. These deformations are a great asset in the masonry applications, but hinder the usefulness of rebar as a threaded fastener.

Rebar gauges (diameter of the bar) are measured in eighths of an inch. For example, #8 rebar is essentially 1″ diameter (8 x 1/8″ = 8/8″ or 1″).

Cut Threading Rebar

Why can’t you just put threads on rebar?

Rebar cannot simply be cut threaded to the nominal diameter. This is due to the diameter difference between the major diameter of UNC threads and the diameter inside the deformations. The diameter inside the deformations is less than the minimum allowable major thread diameter. This will lead to incomplete threads and the liability that comes with product not meeting dimensional tolerances. As an example, the diameter on #8 rebar between the deformations is .960 and the minimum allowed major diameter on 1″ threads is ..

How to properly cut thread rebar

The only way to correctly thread rebar is by turning down, or milling the end of the rod so that it is the proper size and shape to be threaded. This is done by removing the outer layer of the bar until the diameter is equal to the deepest deformation on the bar, leaving a smooth surface to thread. The smaller diameter of the threaded portion means that a larger size of rebar will have to be used and turned down in order to have threads that are the correct nominal diameter. If we go back to our example rebar above, we would need to use #9 rebar, instead of #8 in order to have proper 1″ UNC threads.

Things to keep in mind when ordering threaded rebar

In cases where plans call for threaded rebar, it is essential that the engineer or detailer specify the diameter of thread needed on the bar, since cut threading a #8 rebar will not result in a complete 1″ UNC thread. When thread type is not specified or ambiguous, Portland Bolt makes the assumption that the design requires a 1″ thread and when cut threading, will use a #10 bar to produce a fully functional 1″ – 8 threads per inch Unified National Coarse thread as opposed to cut threading a #8 bar which results in a 3/4″ – 10 thread per inch finished product.

Roll Threading Rebar

As opposed to cut threading, the threads on rebar can also be produced through a roll threading process. For the differences and limitations of roll threading versus cut threading, refer to our FAQ discussing roll threading versus cut threading. Keep in mind that roll threading equipment is limited in the marketplace and many companies that produce threaded rebar will not have the equipment available to roll threads. Most machine shops and smaller scale bolt manufacturing companies only have equipment that is capable of cut threading.

Unlike the cut thread example above, rebar can be turned to the pitch diameter (.912″ in our example using #8 rebar) and rolled back up to produce a fully functional, dimensionally correct 1″- 8 UNC thread. Since some roll threading equipment has diameter and length limitations, rolling threads on rebar is sometimes not possible. Again, the thread dimension in addition to the size of the rebar should be specified.

To specify threaded rebar properly, our inquiry for this example should read as follows:

#8 (1″-8 UNC) x 48″ long A615 grade 60 rebar with 8″ thread one end.

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