This post will discuss the various types of CNC Mills, the pros and cons of each machine, and where they fit in the manufacturing world. This series intends to help people entering the manufacturing world for the first time and help them decide which is best for their needs. Although there are numerous specifics about CNC mills, this post won’t get lost in the technical language and will instead concentrate on the most crucial details.
CNC Vertical Mills
What makes a Vertical Mill a Vertical Mill is the orientation of the cutting tool. The cutting tool is located vertically above the table. The workpiece table is a flat and
horizontal surface where a vise, fixturing, or the actual part to be machined is mounted.
They typically have three programable axis X, Y, & Z, and most can add a 4th axis rotary table if necessary. These types of machines are the most common in shops today due to their cost, size, and ease of operation. Most start-up shops begin with a vertical mill and eventually grow into other types of CNC machines over time.
The Advantages
- Setup: Unlike a horizontal mill, a vertical mill uses gravity to help mount the workpieces, making setup much simpler.
- Versatility: Unlike a horizontal mill, the work table of this equipment is notably more spacious, facilitating the simultaneous installation of multiple fixtures or vises. This capability enables the efficient setup and execution of multiple tasks simultaneously.
- Compactness: Vertical mills are a better choice due to their more compact design taking up less floor space with their efficient layout.
- Popularity: The widespread adoption of CNC mills has resulted in a multitude of brand options available in the market, making it easier to find experienced operators due to the abundance of skilled professionals in this field.
- Efficiency: If your part volume is low or you are engaged in prototyping work, a vertical mill outperforms other types of mills.
The Disadvantages
- Efficiency for high-volume machining: Vertical mills are not the most efficient choice for high-volume machining due to the need to stop and load fresh parts, resulting in lost machining time. This can lead to reduced productivity and longer cycle times.
- Chip control challenges: Vertical mills, especially when dealing with longer cutting parts, can face issues with chip control. The flat horizontal work surfaces of vertical mills can lead to chip buildup on the table, which, if not promptly removed, can cause problems and result in increased downtime.
- Operator availability: Running vertical mills with high efficiency often requires the frequent presence of an operator to load parts more frequently, which can impact production scheduling and labor requirements.
CNC Horizontal Mill
Horizontal mills feature a horizontal orientation for the cutting tool, while the workpiece is mounted vertically on fixturing known as a Tombstone. These Tombstones have multiple sides, ranging from two to eight, allowing for the attachment of part fixtures or vices. In some cases, the workpiece is directly mounted on
the Tombstone. Additionally, horizontal mills have X, Y, and Z axes for movement, and they always incorporate a 4th axis, commonly referred to as a B-axis. Compared to vertical mills, horizontal mills are typically larger in size and are well-suited for high-volume production.
The Advantages
- Efficient Chip Evacuation: The horizontal orientation of the spindle aids in the efficient evacuation of chips during machining, reducing the chances of chip buildup and potential interference with the cutting process.
- Automatic Pallet Changer (APC): Horizontal mills typically come equipped with an Automatic Pallet Changer (APC). This nifty feature enables the machine to work continuously. While one set of parts is being machined on a loaded tombstone, the second tombstone can be loaded with fresh parts. This smart setup reduces idle machine time, making the milling process more efficient and productive.
The Disadvantages
- Higher Cost: The cost of the Horizontal mills tends to be more expensive, making them less accessible for budget-conscious individuals or smaller workshops.
- Larger Footprint: Horizontal mills generally require more floor space due to their larger size and horizontal orientation.
- Complexity: The setup of these mills can be more complex and cumbersome than Vertical mills as gravity is working against you when loading parts or fixtures.
In conclusion, the choice between vertical and horizontal milling machines depends on various factors and your specific machining requirements. It is important to consider the specific machining needs, available space, budget and desired precision when deciding between vertical and horizontal milling machines. Ultimately, selecting the appropriate milling machine involves a thorough evaluation and careful consideration of the pros and cons outlined above.
