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What is Center Drill? Definition, Types, and Applications
In CNC machining, we come across various challenges. For instance, determining a starting point for drilling a shaft. Now the problem in this scenario is that the drill deviates from its initial point. The solution to this is a center drill. If you want to know what center drill is, its types, and applications, then continue reading the blog.
What is Center Drill?
Center drill is one of the various tools used in CNC machining for drilling holes. A center drill is a short drill that features a pointed tip and a wider (cone-shaped) body. It is used to drill small pilot holes in the metal workpiece. These holes serve as a guide for drilling larger holes in shafts and to secure the workpiece to the lathe.
Center drills have other applications as well, which we’ll discuss in the next section. Let’s take a look at the design of this tiny tool:
Pilot
Pilot is the small, pointed, rigid, straight-edged tip of the center drill. The primary purpose of a pilot is to locate the axis. You might be thinking, but why can’t we just start with a regular drill? Well, if you directly start drilling with a twist drill, its chisel point rubs and pushes the material.
This instability will eventually wander off the drill from the center point. For this reason, we use pilot holes as the starting base of drilling.
Countersink
The countersink is the wider part of the center drill. It supports the workpiece and provides structural stability.
Types of Center Drill
Center drills come in various shapes and sizes. They can be classified based on the material type and geometry.
Based on Material
HSS
One of the most common types of center drills is speed steel drills. The machinists use it for drilling soft to medium-hard materials as it can resist chipping and breaking. If you use HSS on harder materials, you’ll end up failing.
Cobalt
Cobalt center drills are basically HSS drills with a higher percentage of cobalt. Cobalt increases the wear and heat resistance of center drills.
Carbide
Carbide is extremely hard and can withstand high temperatures. Due to its rigidity, it has a much higher RPM and feed rate. If you are aiming for larger production runs, a carbide center drill can provide maximum accuracy and longer tool life.
Based on Geometry
Type A
Type A is the most basic type of center drill with a 60° conical angle. It follows the DIN 333-A standard. This type of center drill is used for creating center holes or spotting holes in shafts.
Type B
Type B center drill has 2 chamfers for enhanced performance. It is based on the DIN 333-B standard. This center drill has a 60° countersink and 120° protective chamfer. This 120° chamfer protects the 60° cone from being damaged during the application.
Type R
As compared to type A and type B, type R has a very different geometry. It features a radius instead of a chamfer. It has a pilot tip followed by a curved section. This advanced design provides various advantages in machining.
Uses of Center Drill in Machining
In the machining industry, precision is non-negotiable. You need to meet the requirements of tight tolerances. And sometimes, achieving those can become difficult. Center drilling is a small step that can save you a lot of time and rework. Here, we have included some of the common uses of center drilling in the machining process:
Creating a Center For Long Parts on a Lathe
If you directly start drilling a long rod on a lathe, it will bend, vibrate, and you’ll end up with a poor finish. So, instead, you use a center drill to drill a 60° cone into both ends. These holes serve as a support point. Now, it will fit perfectly, and it won’t slip or shift.
Drilling Pilot Holes
Pilot holes serve as a guide for deep holes drilling . This prevents wandering off-axis. When you begin the drilling operation with pilot holes, you’ll get a smooth and polished surface.
Chamfering
Oftentimes, machining produces sharp edges of drilled holes. These sharp edges can cause a lot of problems while handling the parts, like cutting your hands. Chamfering means creating an angled edge of the hole. Chamfering not only prevents injury but also ensures smooth assembly.
Step-by-Step: How to Use a Center Drill
Let’s go through the steps of using a center drill:
- The first step is to choose the right type of center drill for your process. The right type of center drill is based on the diameter of the workpiece. So, measure the diameter of your workpiece using calipers and select the tool.
- The next step is to tightly secure the workpiece and the center drill. The workpiece is secured using a three-jaw chuck holder. These steps are very important to ensure that there is no wobbling during the machining.
- Depending on the material of the workpiece and the diameter of the center drill that you are using, adjust the rotational speed.
- Now you have to turn on the machine. Bring the center drill down slowly and make sure it touches the metal workpiece.
- Once the process is done. Turn off the spindle and inspect the hole. Your workpiece is now ready.
Choosing the Right Type Of Center Drill
Before choosing the type of center drill (A, B, R), consider your requirements. Whether you need high precision, heavy grinding, or some everyday work. Here’s when you should select each type:
Type A
Type A is suitable if you are doing some general purpose-everyday work. It is versatile and can perform light-duty jobs. You can use it for spotting and chamfering, but do not use it for precision-critical components. In heavy-duty work, it can easily get damaged due to its exposed center point.
Type B
The protective chamfer of the type B center drill protects its center point. If you need extra hole protection, then go for type B. It is ideal for high-precision work.
Type R
If you are working with hard materials and need heavy grinding, then in this case, type R is your option. Its curved style handles stress better and will last longer under tough conditions. Type R provides maximum tool life.
Conclusion
In a nutshell, a center drill is one of the various tools used in machining for drilling holes. There are three types of center drills used for varied operations. A center drill basically performs the basework for subsequent complex operations. Contact Sundi for Cutting tools for PCD, PCBN, and Carbide cutting tools.
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