MILL 1550 IMM Level 1 - Theory Layout – Basic Lines

MILL 1550 IMM Level 1 - Theory Layout: Basic Lines

General Overview

  • Course Code: MILL 1550
  • Focus: Theory and practical application of layout in machining.
  • Key Layout Types: Basic Lines (Straight, Parallel, Perpendicular, Circular, Angular)

Course Objectives

  • Accuracy: Lay out basic lines on a workpiece to an accuracy of ±1/64”.
  • Tools and Techniques:
    • Lay out straight lines using combination square and surface gauge.
    • Lay out hole centers, arcs, and circles.

Layout Operations

Scribing Straight Lines

  • Definition: The most basic operation in layout work.
  • Importance: Straight lines must be accurately marked for precise machining.
  • Edge Requirements:
    • Two adjacent edges of the workpiece must be straight and square (90°) to each other.
    • All measurements taken from these straight edges.

Tools for Laying Out Straight Lines

  1. Combination Square:
    • Utilized to check the 90º angle.
  2. Machinist Square:
    • Used by holding the body against an edge and scribing along the blade for perpendicular lines.
    • Scribe parallel lines using the end of the blade.
  3. Scriber:
    • Developed in conjunction with tools such as height gauges, toolmaker's squares, and surface plates.
  4. Hermaphrodite Calipers:
    • Utilize odd legs to scribe lines parallel or at a specific distance from an edge.
  5. Surface Plate and Height Gauge:
    • Combine both for utmost precision in laying out straight lines.

Layout of Lines Parallels and Angles

  • Perpendicular Lines:

    • Layout perpendicular (Right Angle or 90°) lines using:
    • Machinist square or square head - scribed against a datum edge.
    • Surface gauge or height gauge - involves turning the workpiece at a right angle.

  • Angular Layout:

    • Various angles can be laid out using:
    • Square Head: Common for 90° and 45° angles.
    • Protractor: For degrees; an angle is set and marked.
    • Bevel Protractor: More accurate for angles down to 5 minutes of a degree.

Bisecting Angles

  • Utilize Dividers to quickly bisect (cut in half) an angle.

Layout of Circular Elements

  • Tools for Scribing Circles/Arcs/Radii:
    • Dividers: Most common tool for circles and arcs.
    • Radius Gauges: Useful for small arcs; can be efficient replacements for dividers.
    • Trammels: For larger circles or arcs.

Step-by-Step Scribing Arcs, Radii, Circles

  1. Using Dividers: Set a radius with a steel ruler; mark from the edge of the part.
    • Method: Place one leg at the center punch mark, adjust to desired radius, maintain inclination towards the direction of travel.
  2. Using Radius Gauges: Placed along scribed lines or edges, can be used for internal or external shapes.
  3. Employ Trammels:
    • Set using long steel rule or existing lines; one end held at center punch mark while the other traces the arc.

Locating Centers of Materials

  • Methods for locating the center of round or shaped objects:
    • Hermaphrodite Calipers: Measure by intersection of scribed arcs.
    • Centre Head and Rule: Provides a clear staking of the center in relation to geometry.
    • Height Gauge and Surface Gauge: Allow precise scribing of center-line intersections.

Permanent Layout

  • Once scribed, layout lines should be permanently marked to maintain visibility and accuracy during handling.
  • Techniques include:
    • Prick Punching: For visible layout reference.
    • Automatic Center Punches: Produce uniform marks for improved layout.

Geometry and Layout Relationship

  • 3-4-5 Triangle Method: Essential for accurate layout marking.
    • Using Pythagorean theorem: a^2 + b^2 = c^2
    • Example: 3^2 + 4^2 = 5^2
      ightarrow 9 + 16 = 25

Resources for Further Study

  • Krar, Gill, Smid, Technology of Machine Tools, McGraw Hill.
  • Alberta Apprenticeship and Industry Training, ILM Series, Millwright Manual.
  • The L. S. Starrett Company materials.