Understanding Milling Machine Operations & Best Practices
Milling Operations Explained
This document details common milling operations and best practices.
Types of Milling Operations
Planned: This is the most common operation, used to machine flat surfaces. It can be done by two procedures:
- Face Milling: Using a blade plate or a tapered two-cut plan.
- Tangential Milling: Using a plan to drill a cut.
There are two main types of milling based on the cutter’s rotation relative to the workpiece:
- Conventional Milling (Up Milling): The cutter rotates in the opposite direction to the workpiece’s feed.
- Climb Milling (Down Milling): The cutter rotates in the same direction as the workpiece’s feed. The machined surface may appear flat but will have a series of undulations.
Slotting: This involves creating grooves in the workpiece. Types of slots include:
- Open Slots: Made with slotting cutters with 1 or 3 cuts.
- Angular Slots: Made with angular cutters.
- T-Slots: Machined with T-slot cutters. A central slot is often created first for shaft passage.
- Keyways: Slots made in a shaft. These can be:
- Open: Using cutters with 1 or 3 cuts.
- Closed: Using cutters with 2 flutes.
Parting/Cutting: A groove is created to cut a piece. It’s used to obtain pieces from a bar with the desired profile, using a saw-mill cutter.
Profiling: Used for parts, or sections of parts, with specific profiles, usually curved or complex curvilinear shapes. A combination of cutters, called a cutter train, is often used. For curved profiles, specific cutters are used as needed.
Gear Cutting: Refers to the machining of gear teeth. It’s typically done with constant profile cutters, often referred to as module cutters.
Drilling: This operation is performed on the milling machine for precise holes that must be located at a specific distance from the contour of the part or other holes. The drill bit is driven by the torque or cutting action of the milling machine.
Cutter Positioning Techniques
There are several methods for positioning or adjusting the cutter:
- Adjustment by Test Pass: The correct measurement is achieved by using a dial indicator to check the table’s movement.
- Adjustment by Touch: A practical method where the workpiece is approximated until the spinning cutter makes contact. This friction point is used as the origin.
- Prismatic Parts: For machining a flat surface, the cutter is brought into contact with the workpiece. The workpiece is then removed, the drum is set to zero, and the table is raised by the number of divisions corresponding to the depth of the pass.
- Cylindrical Parts: For milling a slot on the top of a cylinder, the cutter is brought into contact. After removing the piece, it’s moved a length equal to the radius of the piece plus half the thickness of the piece.
- Positioning by Design: Used when the cylinder is mounted on a universal dividing head. The center of the cylinder is located with a gauge. The scriber is then moved half the width of the slot, and a mark is made. The dividing head handle is turned a specific number of turns (e.g., 20), and another mark is made. The cutter is positioned between the two marks, and the touch is made.
- Coordinate Positioning: Uses the precision of the graduated drums based on the principle that every point in space is designated by three axes (X, Y, Z).
Milling Machine Maintenance
- Frequently grease the rotating and sliding parts of the machine.
- Keep the sliding surfaces of the carriages clean.
- Clean the table before placing any accessories on it.
- Thoroughly clean the table after finishing the workday.
- Avoid sudden impacts of the workpiece with any type of cutter.
- Avoid excessive slack in the carriages.
- Avoid strong passes on small or worn machines.
Milling Machine Safety Standards
- Select the milling machine best suited for the job.
- Choose the most suitable cutter and ensure it is very sharp.
- Ensure the table or the workpiece does not collide with any part of the machine during movement.
- Securely clamp the workpiece.
- Measure with the machine stopped.
- Clean chips with a brush.