Precision Machining: Safety, Cutting Speeds, and Metrology

Machining Workshop Essentials

Safety and Fundamental Machining Principles

• Personal Protective Equipment (PPE): Always use safety equipment such as gloves and eye protection.
• Workpiece Rotation: The workpiece must always rotate against the cutting edge.
• Plate Rotation: Avoid sudden changes in the rotation of the machine plate.
• Counterpoint Usage: It is very important to focus tools with a counterpoint. For longitudinal feed, always use a counterpoint if the part length exceeds 2 times its diameter.
• Drill Point Speed: The default drill point speed is 1500 rpm.

Cutting Speed Formula

The formula for calculating cutting speed (N) is:

N = (1000 ⋅ Vt) / (M ⋅ Diameter)

• N: Speed (rpm)
• Vt: Cutting speed (m/min)
• Diameter: Diameter of the part or tool (mm)
• M: Pi (π ≈ 3.1416)

Optimizing Cutting Speeds for Steel

For general use steel (F-1006) with high-speed machining steel, consider the following cutting speeds:

• For drilling holes: 15 m/min
• For grinding: 30 m/min
• For finishing: 45 m/min

Metrology Fundamentals and Tools

Key Metrology Concepts

• Measure: The operation by which the magnitude of one quantity is determined relative to another, taken as a unit.
• Compare: The operation of examining two or more objects or geometric elements to discover relationships or similarities.
• Verify: To check if something is true. In mechanical engineering, verification is essential for quality control.

Metrology Instruments

Micrometer

The micrometer is an instrument used to achieve more accurate measurements than those obtained by rules or calipers.

• An external micrometer is often called a Palmer micrometer.
• Internal micrometers are simply referred to as micrometers.
• Micrometers are classified according to their measuring range and capacity. Their primary principle of operation is based on the screw-nut mechanism.

Comparators

Comparators are used for:

• Verification of the parallelism of two faces.
• Checking the roundness and concentricity of shafts and holes.
• Similar precision measurement applications.

Gauges

In mechanical engineering, the word 'gauge' is used in several ways:

• As a thickness gauge for sheet metal and wire.
• As an instrument for measuring play or backlash.
• As a tool for the verification of profiles and radii.

Thickness Gauges

Used for quick checks of small holes or gaps. By combining two or more leaves from the same set, intermediate measurements can be obtained.

Profile Gauges

There are two main types:

• Radius Gauges: Used to check the roundness of machined parts for sketching and also for verification during execution.
• Special Profile Gauges: These gauges are custom-made and must be constructed with high precision for specific applications.

Reaming Operations

Reamer (Escariador)

Reaming (Escariado) is the final review process for drilled holes. A reamer is a tool specifically designed to finish drilled holes to precise dimensions and surface finishes.

Reamer Components and Types

A reamer typically consists of a handle, a body, and a tip. Reamers are classified into two main types:

• Hand reamers
• Machine reamers

Reamer Grooves and Angles

• Reamer grooves can be straight or helical.
• Grooves can be spaced evenly or unequally (equidistant from the edge).
• The angles of reamers may vary depending on the application.
• The grooves are designed to provide appropriate cutting angles and an outlet for chips.
• The shape of the slots must also vary depending on whether the reamer is used by hand or machine, and the material being worked.
• Extensible reamers have a variable turning diameter.

Reamer Usage and Lubrication

• Direction of Rotation: If a reamer is inserted without spinning, it will get stuck. If turned in reverse, it will become dull. Always turn in the correct cutting direction.
• Lubrication:
  • Bronze, brass, and cast iron are often worked dry.
  • Oil or coolant is used for steel.
• Reamer Shape: Reamers can be cylindrical or tapered.