End mills are highly versatile tools in milling operations. They can perform a variety of cuts, from profiling to slotting. However, many wonder if end mills can also handle plunging. Plunging involves cutting directly downward into the material. This capability depends on the type of end mill, its design features, and the machining material.
In this article, we’ll explore what an end mill is, what a plunge is, and how to plunge with end mills effectively.
What Is End Mill?
End mills are cutting tools employed in machining processes. End mills have a cylindrical shape with cutting edges on the bottom and sides. End mills are available in various sizes, shapes, and materials, each designed for a specific use and material. End mills are essential in CNC operations for precisely and accurately shaping raw materials into finished components. The end mill rotates rapidly as the machine’s control system directs its movement along predetermined pathways. This enables accurate cutting operations to be performed by the design standards.
End mills are flexible equipment that can be used for various cutting activities, such as facing, profiling, slotting, drilling, and contouring. You can also plunge cut with an end mill, but we’ll cover that later in this post. These instruments remove material from a workpiece, resulting in flat surfaces, pockets, holes, and complex shapes. The flute design of an end mill, which refers to the grooves or channels running along its length, aids in chip evacuation and prevents tool binding when cutting.
The suitable end mill cutter for a certain operation is determined by several factors, including the machining material, the desired surface finish, the cutting parameters, and the part geometry’s complexity. Different varieties of end mills, such as square end mills, ball nose end mills, corner radius end mills, and tapered end mills, each have advantages and are chosen based on the application’s needs.
What Is Plunge?
Plunging is a type of milling process in which the tool moves straight down into the workpiece rather than along a horizontal or angled path. The bit is designed specifically for vertical entry in traditional drilling, which efficiently creates holes. Plunging with an end mill is different, as end mills are typically designed for side-to-side cutting rather than direct downward movement.
When using an end mill to plunge, the tool’s geometry plays a significant role. Not all end mills are designed for plunging, and using one that isn’t optimized for this motion can lead to chipping, tool breakage, or poor surface quality. Generally, you need either a center-cutting end mill or a specialized plunge mill for plunging. Center-cutting end mills have cutting edges that extend to the tool’s center, allowing it to bite into the material as it moves vertically.
Plunging can also be used as the initial step to create a starting point before other milling operations. For example, when machining pockets or cavities, a plunge cut helps create a starting hole, allowing the end mill to proceed with side-cutting operations. This versatility makes plunging with an end mill valuable, but only when used correctly and with the correct setup. Key factors like feed rate, spindle speed, and plunge depth must be adjusted carefully to avoid tool damage and to maintain precise control over the cut.
How to Plunge with an End Mill
Plunging with an end mill requires precision, the right type of tool, and careful adjustments to speed, feed rate, and depth. Here’s a step-by-step guide on how to effectively plunge with an end mill:
Choose the Right End Mill
For plunging, select a center-cutting end mill designed specifically for vertical cuts. A center-cutting end mill has cutting edges that meet at the tool’s center, which allows it to cut straight down into the material. Standard end mills without a center-cutting design can’t cut effectively from the middle, which can cause the tool to skip or jam.
An end mill with fewer flutes helps clear chips more effectively during plunging. A specialized plunge end mill can also work if a standard center-cutting option isn’t available.
Check Tool Parameters
The size and length of your end mill play a crucial role in plunge performance. For shallower plunges, a smaller diameter end mill can offer better control and less deflection, but if you need to remove more material, a larger diameter provides better rigidity. Tool length is also essential; while a longer end mill can reach deeper, it’s more prone to deflection and chatter, which may affect accuracy. Always choose the shortest tool possible for the desired plunge depth to maintain stability.
Adjust Spindle Speed and Feed Rate
Setting the feed rate and spindle speed is crucial to effective plunging. Begin with a moderate spindle speed lower than you’d use for side milling. For example, if you’re used to running at 10,000 RPM for side milling, you may start around 6,000-7,000 RPM for plunging. A slower speed helps control heat buildup and prolongs tool life.
The feed rate should also be reduced, as a high feed rate can overload the tool. Starting with a feed rate around 25-50% of your standard side-milling rate is usually a safe bet, allowing you to increase gradually as needed.
Set Plunge Depth and Approach
Trying to reach the full depth in one plunge can overburden the tool, causing it to break or wear prematurely. Use a pecking approach to plunge into small, incremental steps. For each peck, set a depth approximately 1-2 times the tool’s diameter, then retract slightly to clear out chips before moving deeper. For instance, if you’re using a 10mm CNC end mill, you might plunge 10-20mm at a time before retracting.
This approach reduces heat buildup, removes chips effectively, and minimizes stress on the tool, enhancing both cut quality and tool lifespan.
Ensure Proper Coolant and Chip Evacuation
Coolant and chip removal are vital for plunging with an end mill. Since plunging generates heat, applying coolant prevents overheating, which could degrade tool performance. You can use air to blow chips out of the cut or apply coolant directly for better chip evacuation and temperature control. Chips may accumulate around the tool without adequate chip removal, causing it to jam or affect surface quality.
Some machinists use mist cooling for better visibility and cooling, while others rely on flood coolant for high-volume operations.
Monitor and Adjust as Needed
While plunging, watch the tool and listen for any unusual sounds, such as squealing or vibration, which might signal tool strain or instability. Chatter often indicates that adjustments to the feed rate, spindle speed, or tool length are needed. If you hear chatter, reduce the feed rate and check if the tool length or depth of cut might be causing deflection.
Regularly inspect the tool for wear or heat discoloration, which indicates that speed and feed adjustments are necessary. Minor adjustments during the process help you maintain control, prolong tool life, and achieve smoother results.
Conclusion
Plunging with an end mill can be a practical and efficient method. Although traditionally used for horizontal cuts, end mills, especially center-cutting types, can perform vertical plunges effectively with the proper setup. Choosing the appropriate tool, setting the correct spindle speed, adjusting the feed rate, and using the appropriate technique all contribute to a successful plunge operation. Proper chip evacuation and cooling further help maintain tool life and cut quality. By following these guidelines, machinists can unlock the complete versatility of end mills, using them confidently for both plunging and side milling tasks.
