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A Complete Guide on Thread Taps-Everything You Need to Know
Threading taps are widely used in metalworking and machining industries to produce threaded holes for fastening bolts, screws, and other threaded components. Different thread taps are available in the market, but how do you choose the correct one? How to use it? Please refer to the article below to get the answers.
What Is A Thread Tap?
A thread tap is a tool that is used to cut threads for screws. These threads are used to fasten bolts or nuts together. A typical thread tap has a pointed end with grooves that help remove chips and debris while cutting into the material. It’s widely used in the manufacturing industry.
Tap Structure
Machine and hand taps are commonly used for cutting standard threads. High precision and speed steel grinding taps are called machine taps, while carbon tool steel or alloy tool steel rolling (or cutting) taps are called hand taps. However, the structure and working principles of the two are essentially the same. A tap typically consists of a working part and a handle. The working part is divided into a cutting element and a calibration part. The cutting part has a cutting cone to perform the cutting work, while the calibration part is used to adjust the size and shape of the thread.
Tap Classification
Tap classification can be divided into four categories:
1. Classified by drive: hand tap and machine tap.
2. Classified by processing method: cutting tap and extrusion tap.
3. Classified by processed threads: metric coarse thread taps, metric fine thread taps, pipe thread taps, etc.
4. According to their shape, they are divided into straight groove taps, spiral groove taps, and spiral pointed taps.
A straight groove tap is a tool used to cut threads in a hole. Unlike a spiral groove tap, it has a straight groove that runs along the length of the tap. This design is simpler and makes the tap easier to manufacture, but it can also make removing chips and debris from the hole more difficult.
Spiral pointed tap is a useful tool for tapping through holes, similar to a hand tap. However, the first few threads are angled to make it easier to remove chips. This feature makes it the perfect choice for high-speed production work.
A spiral groove tap is more suitable for processing non-perforated threads or blind holes. Due to the helix angle, the actual cutting rake angle of the tap will increase with the increase of the helix angle. Therefore, when processing materials with higher hardness, the spiral angle should be smaller, typically around 30 degrees, to ensure its rigidity and prolong the lifespan of the tap. Processing non-ferrous metals such as copper, aluminum, magnesium, and zinc, which have lower hardness, requires selecting a larger helix angle, which can be around 45 degrees, resulting in sharper cutting and better chip removal.
How To Use A Tap For Threading?
1. To start tapping, insert the tap into the hole and ensure that the center line of the tap is aligned with the center line of the hole.
2. Rotate the tap evenly and apply gentle pressure to feed it into the hole. Do not apply additional pressure once the tap has started to feed.
3. Reverse the tap by about 45 degrees each time to cut the chips and prevent blockages.
4. If the tap becomes difficult to rotate, do not force it. Applying more rotational force will cause the tap to break
How to Choose The Right Tap Type
Properly selecting a tap to process internal threads can ensure the quality of thread connections and improve the service life of the tap.
Common thread standards
There are three common standards for choosing regular threads: metric, imperial, and Unified.
The metric system(The American National pipe thread) is a thread with a tooth angle of 60 degrees measured in millimeters. For example, M8X1-6H represents a metric fine-pitch thread with a diameter of 8 millimeters, a pitch of 1 millimeter, and an internal thread tolerance zone of 6H.
The British system(The BSP, or Whitworth thread) is a thread with a tooth profile angle of 55 degrees, measured in inches. For example, BSW 1/4-20 represents a diameter of 1/4 inch, with a coarse pitch of 20 teeth per inch. This type of thread is rarely used.
Another unified system(Unified Thread Standard (UTS)) is for threads with a tooth profile angle of 60 degrees in inches.
Diameters less than 1/4 inch are commonly called numbers, with numbers 0 to 12 representing diameter specifications ranging from 0.06 inches to 1/4 inches. The United States primarily uses Unified Screw Threads.
Choose the type of tap
We often use straight groove taps, spiral groove taps, screw tip taps, and extrusion taps, each with their strengths in performance.
Straight groove taps are versatile and cheap but have poor targeting. Spiral groove taps are better for non-perforated threads, with chips discharged backward due to the helix angle.
Experience tells us that when processing black metal, the spiral angle should be selected to be smaller, usually around 30 degrees, to ensure the strength of the spiral teeth. For processing non-ferrous metals, choose a larger helix angle, around 45 degrees, and the cutting is sharper. When machining threads with a screw tap, the chips are discharged forward. Squeezing taps are more suitable for processing non-ferrous metals.
Tap Maintenance Tips
Maintenance is also essential to the lifespan of the taps. Good maintenance could save costs and make the taps used much longer.
1. When tapping, make sure to chamfer the end face hole. The tap should be aligned with the hole of the workpiece. Apply axial pressure at the beginning of tapping to allow the tap to cut in. After a few turns, axial force is no longer required.
2. After the calibration part of the tap enters the screw hole, retract it by 1/4 or 1/2 turn for every half turn to one turn. It will break the chips before attacking downwards. When tapping through holes, frequently exit the tap for chip removal.
3. While tapping on steel workpieces, add cutting fluid. When tapping on cast iron workpieces, add a small amount of kerosene. After using the head attack, when using the second or third attack, screw the tap into the screw hole.
4. When threading, chamfer the end of the workpiece, and make sure the end face of the wrench is perpendicular to the axis of the workpiece. Apply axial pressure at the beginning of threading, and the corresponding rotational force should be greater. When cutting threads on the workpiece, do not apply any more pressure.
5. To break the chips and discharge them promptly while threading, frequently reverse and pull the teeth.
6. Firmly fix the workpiece on the clamp and fixture. If the tap gets broken, do not touch the area with your hands. Use a chisel or sample punch to remove it. When the thread is broken, wear protective goggles.
Tap Threading Operation Tips
(1) The opening of the threaded bottom hole on the workpiece should be chamfered. Both ends of the through-hole thread should also be chamfered.
(2) The workpiece clamp should be positioned correctly, and the centerline of the threaded hole should be placed in a horizontal or vertical position as much as possible. It will allow for easy determination of whether the tap’s axis is perpendicular to the plane of the workpiece during tapping.
(3) try to place the tap as straight as possible at the beginning of tapping. Then, apply pressure to the tap and turn the wrench. After cutting 1-2 turns, carefully check and correct the position of the tap. When cutting 3-4 turns of thread, ensure that the position of the tap is error-free. In the future, only turn the wrench and not apply pressure to the tap. Otherwise, the thread profile will be damaged.
(4) During tapping, for every 1/2 to 1 turn of the wrench, reverse it by about 1/2 turn. It will make it easier to discharge the broken chips and reduce the cutting edge being stuck by the tap due to chip sticking.
(5) When the screw hole cannot be penetrated, frequently remove the tap to eliminate chips from the hole.
(6) When attacking the screw holes of plastic materials, add lubricating coolant. Oil or concentrated emulsions with higher requirements can be used for steel materials, such as vegetable oil or molybdenum disulfide. For stainless steel, use grade 30 engine oil or vulcanized oil.
(7) To change to the next tap, screw it into the already tapped thread by hand until it cannot be screwed in any further. Then, use a wrench to turn it. Do not turn the wrench quickly when exiting after the final cone attack. Instead, use your hand to rotate it out to ensure that the quality of the already tapped thread is not affected.
(8) Ensure that the tap and screw hole remain coaxial during the machine tapping process.
(9) The calibration part of the tap cannot be completely protruding during machine tapping. Otherwise, it will cause loose teeth when exiting the tap in reverse.
Tap Anodizing
Anodizing can enhance tap performance by creating a porous surface layer that has excellent coolant adsorption properties and can reduce friction.
Anodizing is a surface treatment method that involves placing high-speed steel wires in water vapor at 500-550 ℃ to form a Fe3O4 coating on their surface. This method is also known as the high-pressure steam treatment method.
There are three types of iron oxides: FeO, Fe2O3, and Fe3O4. FeO can only be generated above 570 ℃, so it does not exist in the surface treatment layer of high-speed wiretaps. The surface layer of wiretaps contains two types of iron oxides: Fe3O4 (black iron) and Fe2O3 (red iron), which are not conducive to the cutting ability of the taps. After high-quality surface treatment, the treatment layer of the tap is Fe3O4 coated, with a beautiful surface, blue-black color, and a surface thickness of 1-3um.
1. Anodizing Characteristics
Anodizing can improve the performance of a tap because the surface layer is porous, which has good adsorption properties for coolant and can reduce friction. At the same time, it can prevent adhesion between the tap and the material being cut. The grinding stress remaining on the surface of the tap during its production has also been removed.
However, it should be noted that the coating generated by anodizing treatment cannot improve the hardness of the surface layer of the tap, which means the coating itself does not have wear resistance.
2. Scope of Application
Anodized taps have an excellent effect on cutting materials prone to bonding, such as stainless steel, cast steel, carbon steel, nickel steel, chromium steel, etc. They are almost suitable for processing all steel parts.
However, it should be noted that anodizing does not have a perfect effect on non-metallic materials such as aluminum alloys, die-cast aluminum alloys, and brass and may even reduce the cutting performance of the tap.
3. Cutting performance
When using a blade angle tap to process stainless steel (austenitic system) workpieces that are prone to bonding, oxidation treatment can increase the lifespan of the tap by more than 10 times. It can also be seen from the experimental example of NORIS universal tap processing carbon steel, where anodizing significantly improves the lifespan of the tap.
Conclusion
Thread taps are tools used to cut internal threads in drilled holes accurately to fit fasteners where conventional bolts and nuts are not ideal. Manufacturers use different types of taps to thread drilled holes and can use many tapping machining techniques to make custom parts.
Enze makes machining services easy and is the perfect choice for your threading machining projects. Our engineers are experts in tapping techniques. If you have any questions about threading holes, please get in touch with us.
