Chamfers and countersinks prevent burrs forming
Views : 523
Update time : 2018-04-03 20:44:51
The purpose of chamfering or countersinking of internally threaded holes is usually to avoid the generation of raised burrs which can prevent the attachment from fitting to a flat surface of the workpiece. In addition, when the fitting presses on the burr, the burr will be pressed down, which will cause the internal thread to deform and increase the possibility of threading.
Drawing a chamfer or counterbore on a part drawing can also help the bolts align or insert properly. Adding a chamfer or countersink at the location where the hole is to be drilled can help in drilling.
For these reasons, most threaded holes require some type of chamfering or countersinking. Therefore, this is one of the most common processing processes and it is also a place that usually needs improvement.
The angle of thread hole chamfering is usually 120° or 90°, the most common of which is 90°. The outer diameter and depth of the chamfer are sometimes specified on the drawing. However, the mechanic or programmer often decides the depth or outside diameter of the chamfer hole.
In some classic machinist's rules of thumb, the most common practice is to machine chamfer diameters 0.010 inch to 0.015 inch (0.254 mm to 0.381 mm) larger than the diameter of the thread, which will eliminate burrs and provide enough depth to guide the assembly soon. Bolts.
Processing method
There are many ways to machine chamfers or countersinks, and these methods have different machining efficiencies. A common method used in the past is to machine a 120° or 90° chamfer at the hole to be drilled after drilling.
Many machine tool mills use 90-degree-angle CNC drills to complete point drilling, countersunking, and chamfering, which not only saves tool change time, but also reduces tooling costs. The CNC point drill is used as a guide tool and is used to machine a 90° angle before drilling. Although this method is convenient, it is not recommended when drilling with a newer high-permeability cemented carbide drill. Because this kind of cemented carbide drill has a top angle of 140°. After using a 90° point drill, re-drilling with a 140° cemented carbide drill results in corner cuts on the carbide drill and faster tool failure. If drilling with a carbide drill, the sequence of using the tool must be changed.
At this point, the correct tool sequence should be: drilling, chamfering (or countersinking), and spot drilling. In this case, using a countersink or chamfer cutter with an angle of 120° or 90° is the best choice. By selecting the appropriate tool sequence, the tool life of carbide drills will increase significantly.
When performing countersinking of countersunk holes or holes, special attention should be paid to the countersinking. A wrong tool setting will have a large negative impact on the quality and function of the part. When chamfering cutters are used, circular chamfering can be performed by circular interpolation, but this may not be the optimum process for direct chamfering. In contrast, traditional high-speed steel counterbore holes are specifically designed for chamfering, but they are not suitable for helical circular interpolation tool paths.
Merge operations
The most effective and quick way to chamfer a hole is to use a step drill that has both drilling and countersinking capabilities. Because the drill has a countersink angle of 90°, drilling and countersinking can be completed in one step using this step drill.
Combining two machining operations into one not only reduces tool change time, cycle time and tool inventory, but also ensures that the chamfer is concentric with the bottom hole.
If you use a step drill as the preferred method for drilling, you must use a modified standard drill, and the small diameter of the step drill grinds to the diameter of a standard single-diameter drill. The core thickness of the thread path may be too large and affect chip discharge. For the purpose of easy cleaning, thread trails generally have no land, and this also causes excessive friction on the outer diameter, which reduces the tool's performance.
Step drills, especially cemented carbide step drills, should be made of hard alloy rods instead of grinding existing tools to ensure that cores and lands meet the requirements. Standard step drills exist, and some tool makers can quickly provide these products to the end user and can be used to machine blind holes with different tapped hole depths.
Process improvement is the eternal goal of advanced manufacturers. Although the preparation of chamfers and counterbores prior to tapping is a common structure, the processing sequence is not a standardized process and, like most other processes, it still requires excellence.
Drawing a chamfer or counterbore on a part drawing can also help the bolts align or insert properly. Adding a chamfer or countersink at the location where the hole is to be drilled can help in drilling.
For these reasons, most threaded holes require some type of chamfering or countersinking. Therefore, this is one of the most common processing processes and it is also a place that usually needs improvement.
The angle of thread hole chamfering is usually 120° or 90°, the most common of which is 90°. The outer diameter and depth of the chamfer are sometimes specified on the drawing. However, the mechanic or programmer often decides the depth or outside diameter of the chamfer hole.
In some classic machinist's rules of thumb, the most common practice is to machine chamfer diameters 0.010 inch to 0.015 inch (0.254 mm to 0.381 mm) larger than the diameter of the thread, which will eliminate burrs and provide enough depth to guide the assembly soon. Bolts.
Processing method
There are many ways to machine chamfers or countersinks, and these methods have different machining efficiencies. A common method used in the past is to machine a 120° or 90° chamfer at the hole to be drilled after drilling.
Many machine tool mills use 90-degree-angle CNC drills to complete point drilling, countersunking, and chamfering, which not only saves tool change time, but also reduces tooling costs. The CNC point drill is used as a guide tool and is used to machine a 90° angle before drilling. Although this method is convenient, it is not recommended when drilling with a newer high-permeability cemented carbide drill. Because this kind of cemented carbide drill has a top angle of 140°. After using a 90° point drill, re-drilling with a 140° cemented carbide drill results in corner cuts on the carbide drill and faster tool failure. If drilling with a carbide drill, the sequence of using the tool must be changed.
At this point, the correct tool sequence should be: drilling, chamfering (or countersinking), and spot drilling. In this case, using a countersink or chamfer cutter with an angle of 120° or 90° is the best choice. By selecting the appropriate tool sequence, the tool life of carbide drills will increase significantly.
When performing countersinking of countersunk holes or holes, special attention should be paid to the countersinking. A wrong tool setting will have a large negative impact on the quality and function of the part. When chamfering cutters are used, circular chamfering can be performed by circular interpolation, but this may not be the optimum process for direct chamfering. In contrast, traditional high-speed steel counterbore holes are specifically designed for chamfering, but they are not suitable for helical circular interpolation tool paths.
Merge operations
The most effective and quick way to chamfer a hole is to use a step drill that has both drilling and countersinking capabilities. Because the drill has a countersink angle of 90°, drilling and countersinking can be completed in one step using this step drill.
Combining two machining operations into one not only reduces tool change time, cycle time and tool inventory, but also ensures that the chamfer is concentric with the bottom hole.
If you use a step drill as the preferred method for drilling, you must use a modified standard drill, and the small diameter of the step drill grinds to the diameter of a standard single-diameter drill. The core thickness of the thread path may be too large and affect chip discharge. For the purpose of easy cleaning, thread trails generally have no land, and this also causes excessive friction on the outer diameter, which reduces the tool's performance.
Step drills, especially cemented carbide step drills, should be made of hard alloy rods instead of grinding existing tools to ensure that cores and lands meet the requirements. Standard step drills exist, and some tool makers can quickly provide these products to the end user and can be used to machine blind holes with different tapped hole depths.
Process improvement is the eternal goal of advanced manufacturers. Although the preparation of chamfers and counterbores prior to tapping is a common structure, the processing sequence is not a standardized process and, like most other processes, it still requires excellence.