Cutting Internal Complex Holes
For complex internal holes, such as those with a wall around the circumference, internal curves, or blind holes, choosing the right core for the job can be a challenge. Cores are usually chosen based on the settings of the machine and the surface finish required. Internal complex holes can be cut quickly and accurately using a combination of different core methods.
Slotting: This method is best used when cutting slots and is most commonly used in applications where the internal wall finish is not important. The slotting method involves a core pin being inserted into the material, followed by a continuous or interrupted spiral cutting process. During the slotting process, a toolpoint is used to create small slots. The core pin can then be used to fine-tune the machined shape.
Tangential Slotted Core Drilling: This method is used when a very precise hole size and shape are required. The tangential slotted core drill is a combination of slotting and core drilling. Using a sprocket wheel and a tangentially mounted drill bit, the core is inserted into the material. The drill bit is then moved along the wall of the hole at a constant rate. This allows for accurate machining and an even wall finish.
Post Drill Closed-Loop Method: This method is employed when the hole is too deep for core drilling and requires an internal wall finish. A close-loop system consists of a drill bit, a chuck, and a post-hole drilling mechanism. The drill bit is positioned at the base of the hole and the chuck is used to turn the bit. The post-hole drill is then used to machine the sides of the hole. The chuck is then used to move the tool around the circumference of the hole. This allows for very precise machining of the internal wall of the hole.
Thread Rolling: This is a method of producing internal threads in complex holes. The process involves rolling a thread onto a cylindrical shaped core which is then inserted into the workpiece. Thread rolling allows for very precise machining of the threads and makes them stronger and more accurate than other methods.
Although there are many different core methods for cutting internal holes, the key is to choose the appropriate core for the job. Depending on the desired surface finish, the application, and the size and shape of the hole, various core methods can be used in combination to produce accurate and repeatable results. While there is no single “right” way to cut internal complex holes, choosing the right core and tool configuration is the key to achieving the desired result.
