Sine-bar and Combination Set

Definition

A Sine-bar is a high-precision measuring instrument used to measure angles by employing trigonometric principles (sine function), typically used in conjunction with slip gauges. A Combination Set is a versatile multi-purpose tool used in workshops for measuring, marking, and checking angles, center locations, and depths.

Main Content

1. Sine-bar Principles

• It consists of a hardened, ground steel bar with two precision rollers of equal diameter at both ends.
• The distance between the centers of these rollers is the defining length of the sine-bar (e.g., 100mm, 200mm, or 300mm).
• The angle is determined by the formula: sin θ = h / L, where 'h' is the height of slip gauges and 'L' is the distance between roller centers.

2. Combination Set Components

• Square Head: Used for marking 90° and 45° angles and checking flatness.
• Protractor Head: Features a rotating dial that allows the measurement of angles from 0° to 180°.
• Center Head: Used to locate the exact center of cylindrical or circular workpieces.
• Steel Rule: The central base upon which the heads are attached and slid.

3. Visual Representation

SINE-BAR SETUP:
      _______________________
     /                      /|  <-- Sine Bar
    /______________________/ |
   | o                    o  |  <-- Rollers
   |_________________________|
             | |
             | |  <-- Slip Gauges (Height h)
   __________| |___________
   (Surface Plate)

Working / Process

1. Preparation of Sine-bar

• Place the sine-bar on a perfectly flat surface plate.
• Calculate the height of the slip gauges required to achieve the desired angle using the formula $h = L \cdot \sin(\theta)$.
• Stack the slip gauges to the calculated height and place them under one of the rollers.

2. Alignment of Workpiece

• Place the workpiece on top of the sine-bar.
• Use a dial test indicator (DTI) to check the parallelism of the top surface of the workpiece.
• If the DTI reading is zero across the length, the workpiece is set to the required angle.

3. Using the Combination Set

• Slide the required head (Square, Protractor, or Center) onto the steel rule.
• Tighten the knurled nut to lock the head in the desired position.
• Apply the tool to the workpiece; for a center head, touch the two arms against the cylinder and scribe a line, then rotate 90° to scribe another, marking the center at the intersection.

Advantages / Applications

• Sine-bars provide extremely high precision (up to seconds of a degree) for laboratory and tool-room applications.
• Combination sets are highly portable and multifunctional, reducing the need for carrying multiple individual tools.
• Sine-bars are essential for calibrating jigs and fixtures where angular accuracy is critical for machine performance.

Summary

The sine-bar is a high-accuracy instrument for measuring angles through trigonometry and slip gauges, while the combination set acts as a modular, versatile tool for general workshop layout and measurement tasks.

• Important terms to remember: Slip Gauges (Gauge blocks), Surface Plate, Sine Function, Dial Test Indicator, Protractor, Center Head.