Did you know that machining internal threads can be one of the most challenging operations for any machining organization? Furthermore, it is typically one of the final operations, so faulty threads can be very costly.
In this article, we will discuss aspects that influence the quality of your threaded holes, including:
ㆍHolemaking - preparation of the hole before threading;
ㆍThreading method - tapping vs thread milling;
ㆍTool holding - tap holding;
ㆍLubrication - metalworking fluid.
CNC Pipe Threading Machine
The importance of having a good, straight, on-size hole prior to threading cannot be overstated. With modern, high-performance solid carbide drills and machinery (toolholding etc.), drilling "oversize" has been for the most part eliminated.
However, far too many machinists still go by the good old industry standard tap drill charts that have been around for decades. For example:
ㆍMost machinists could recite 17/32" (.5312") dia is the "tap drill" for 5/8-11;
ㆍBut at the time, the expectation was a probable oversize of .0049", a probable hole size of .5362" dia. and 75% thread.
So, a 17/32" modern drill today would typically yield an "on-size" hole, which is too high a percentage of thread and would make a tap work far too hard.
Choosing the right tool for your threading process can be challenging, and that is why it is important to examine your application's needs and get advice from the cutting tool experts. Making a thorough analysis before committing to the tool will generate quality threads in the most efficient and cost-effective way.
The following methods may offer some support in deciding the best solution for your threading process.
Tapping:
ㆍBasic choices include Cut vs Thread-forming taps.
ㆍAbility to produce threaded holes with longer tool life, uniform quality and short cycle times.
ㆍGeneral purpose and high-performance taps can improve thread quality and boost output while reducing production costs. Since these taps can handle most of the common materials (like aluminum, carbon steel, cast iron, stainless steel and steel alloys), they reduce the need to stock several different types of taps.
ㆍFull-speed taps can operate two to five times faster than conventional tools, due to unique design characteristics. In addition, these full-speed taps also have the greatest hard surface coatings existing and coolant-through technology.
CNC Pipe Threading Machine
ㆍTaps produces exceptionally fast tapping at record-level speeds on modern CNC machines. Increased speed generates production savings and efficiency, since speed reduces cycle time while improving thread quality.
Thread Milling:
ㆍThese tools are designed for high cutting feeds and speeds, creating threads with excellent form, finish and dimensional accuracy, due to the capacity of controlling the exact thread depth and position.
ㆍEasy machining of difficult materials, and the production of small controllable chips.
ㆍCombining thread milling with the latest CNC technology can lead to outstanding flexibility, process control, tool life and part quality.
Modern tap holders offer a range of solutions to cover most applications.
Rigid tapping has become more prevalent with modern machine tools. But some mismatch between the controls of a machine and its actual movement has led to the popularity of Tap Holders, which provides some length compensation.
When machining threads, one must consider optimizing lubrication. Modern water-soluble metalworking fluids can go a long way towards producing high quality threads and improving tool life. When the application of metalworking fluids is not practical, one must be sure to use an adequate tapping fluid.
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