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Milling is making objects by removing material from a flat surface with a rotating tool. There are two main ways of milling: co-rotating and counter-rotating (conventional). Both have advantages and disadvantages, making it difficult to choose the right method. In this article, we compare the differences between co-rotating and traditional milling and outline factors to consider when choosing the correct machining method.


What is concurrent milling? 


The process of concurrent milling, also known as downward milling, involves machining material by a rotating cutting tool and workpiece moving in the same direction. One of the benefits of ascending milling is that there is no risk of re-cutting. This is because the teeth of the cutting tool will lift up on the workpiece during milling, releasing the cut chips behind the tool. It is important to note that the process starts with the full thickness of the material, but the thickness decreases as machining progresses.


What is counter-milling? 


CNC conventional milling is a traditional machining method in which the cutting tool rotates opposite to the workpiece. It is also called top milling because the cutting is done upwards in counter-rotating milling. Unlike face milling, with conventional end milling, chip formation starts at zero and gradually increases. In addition, the chips remain in the cutter's path as it rotates upward.


The main differences between co-rotating and counter-rotating milling


Some differences between conventional and ascending milling affect the process and results. However, the main difference is how the tool deflects during cutting. In conventional milling, the tool deflection is parallel to the cut's direction, giving more control over the process and less risk of errors. Conversely, the tool is deflected perpendicular to the cut in upward milling, which can affect cutting width and accuracy. For roughing, ascending milling is recommended because it is faster. In addition, the effect of tool deflection on accuracy is less important because finishing improves part precision.


Metal milling by co-rotating and counter-rotating milling- advantages.


Both processes of milling metal and another machined surface have their advantages, depending on the application. We will evaluate their mechanisms, as they can influence the choice of the method that best suits the workpiece. Analyzing these advantages is important because it can help you choose the best machining method for your workpiece. For example, one method may be faster and more efficient for machining many workpieces, while another method may provide better machining quality, but will require more time and cost. Considering the advantages and disadvantages of both methods is key to choosing the best option.


Advantages of concurrent milling 


Accordingly, we present them here:


Better tool life


Tools used in this milling process generally have a better tool life than those used in traditional milling. This is because the tool is not subjected to high stresses during cutting. Cutting tools used for cantilever milling generally generate less heat and deformation than conventional milling. This reduces tool wear and extends tool life by up to 50% compared to conventional milling.


Better surface finish


As the cantilever milling process progresses, chip thickness decreases, resulting in less deflection during cutting. In addition, cutting during this process causes chips to settle behind the tool, eliminating the need for re-cutting and providing an excellent finish on the workpiece.


Low cutting load and heat generation


Less heat is generated during cantilever milling because the width of the chip decreases as cutting progresses. In addition, with downward directed cutting forces, overall cutting loads and clamping requirements are reduced, especially in horizontal milling. The downward force directed by the tool can also help remove debris during machining, as it firmly holds the workpiece on the surface below it.


Easier to clamp


Cantilever milling works with a downward force, so face milling helps strengthen the workpiece to the surface beneath it, reducing chipping on thin substrates.


Advantages of cantilever milling 


Accordingly, we present them here:


Higher stability

Conventional milling tends to pull the workpiece toward the operator during cutting, while conventional milling works in reverse. As a result, it provides the operator with more control, which translates into greater stability. Conventional milling does not cause excessive vibration compared to concurrent milling. Therefore, it is superior to conventional milling in terms of stability.


Zero play


Zero play is one of the distinguishing factors of conventional milling. This advantage is because conventional milling does not pull the table, thus providing optimal stability.


Best control


During conventional milling, there is a greater tendency for the tool to deviate from the workpiece. This offset provides the least chance of accidental cuts. Moreover, even when such cuts do occur, they are of negligible depth. 


Disadvantages of counter-rotating milling 


Both co-rotating and conventional milling have their advantages, but their disadvantages are also worth noting. Here are some of them. Disadvantages of counter-rotating milling:



This is one of the main disadvantages of conventional milling compared to conventional milling. In the upper spindle, especially where the forces acting on the tool are large enough. Let's explain it better. Up milling is done with a force directed downward. This force usually acts not only on the workpiece, but also on the table, pulling it into the cutting tool. With sufficient clearance, the table can break, causing injury to the operator. This is especially true when the cutting tool is operating at high capacity. However, today's milling machines are equipped with backlash eliminators. It helps reduce it, allowing the machine operator to reap the benefits of high-speed milling without interference.


Excessive vibration


Working at high speeds or machining thick parts can cause strong vibrations when cantilever milling. The cause of these vibrations is the tool's action on the workpiece. These vibrations are harmful because they often cause the tool to deform, which affects accuracy. They can also damage the workpieces.


Not suitable for harder materials


Since chip thickness is greatest at the beginning of cutting in cantilever milling, machining harder materials in this process can damage the cutting tool. This can happen to cut tools made of steel, cast iron, titanium, and other hard materials. So when it comes to milling harder tools, conventional milling is a better choice.


Disadvantages of conventional milling


Accordingly, we present them here:


Coarse machining


The undercutting used in this process makes it difficult to achieve a smooth finish. This is due to the surface roughness caused by the amount of deflection of the workpiece and tool. However, this amount of deflection makes conventional milling ideal for machining harder materials such as steel and cast iron.


Generating too much heat


Another disadvantage of conventional milling is the heat generated during machining. This heat is generated because of the accumulation of chips, which often results in overheating of the cutting tool. The consequence of overheating the cutting tool is a shortened tool life.


Damage to the tool


The friction and upward force generated by conventional milling often generate excessive heat. Excessive heat can also damage the tool, reducing the workpiece's life, precision and accuracy.


Concurrent milling vs. counter-rotating milling-which to choose? 


The right time to choose between upward and downward milling depends on the application, requirements, material, and other factors. In general, when people compare conventional milling with top milling, they often assume that top milling is better because it has minimal stress, offers a better surface finish and ensures tool life over a long period. However, there are better approaches in some cases, as it also has significant drawbacks. Like conventional milling, it has some obvious advantages. However, its limitations are equally important. Therefore, it is crucial to have a thorough understanding of both cutting processes to make sure you make the right choice and get consistent results.


Here are some tips to help you choose between conventional and ascending milling.


  • Prefer lift milling for smaller parts that require a flawless finish.
  • Don't use rising milling for manual milling machines.
  • Make sure the conventional machine you are using has a backlash eliminator for rising milling
  • Use conventional milling for hard and rigid materials or hardened parts.
  • Do not use ascending milling in the first pass if the material is oxidized or has a rough surface
  • For best accuracy, use ascending milling in the last pass.
  • Consider using ceramic inserts to improve your milling technique.