Metrology and instrumentation (M602) Module 2

Gauges:

Gauges are scale less inspection tools at rigid design which are used to check the dimension of measured parts. They do not determine the actual size or dimension of parts. No need of calculations.

Classification

According to type: 1) Standard gauges 2) Limit Gauges According to purpose: 1) Workshop gauge 2) Inspection Gauge 3) Reference / Master gauges According to the form of tested surface: 1) Plug Gauge 2) Snap/Ring Gauges According to the design: 1) Single limit and double limit gauges 2) Single ended and double ended gauges 3) Fixed and Adjustable gauges

Design of gauges

Taylor’s principle of gauge design

Designed by William Taylor Used for design of limit gauges. 1. The Go gauges should be designed to check the maximum material limit while No Go Gauges should be designed to check the minimum material limit. 2. Go gauges should check all related dimensions. No Go gauges should check one element of the dimension at a time.

METROLOGY AND INSTRUMENTATION (M602) -MODULE 2

Gauge maker’s tolerances

Some variations in size will be, due to imperfections in the process. So some allowance must be provided to gauge maker to manufacture gauges.This is known as Gauge maker’s tolerances

Wear allowance

The allowance provided on the Go gauges to counteract wearlosedue to rubbing on the surfaces of work piece.

Gauge materials

Metals having good hardness,corrosion resistance,Good mach inability are used. High carbon steels, Steels coated with wear resisting metals like chromium, tungsten carbide

Form measurements: straightness, flatness, squreness, circularity & cylindricity – Measurement of angles & tapers: sine bars, angle gauges: auto collimator, clinometer & spirit level; taper gauges, bevel protractors.

FORM MEASUREMENTS Straightness Testing Straightedge

A straightedge is a tool with an accurately straight edge used for drawing or cutting straight lines, or checking the straightness of lines. If it has equally spaced markings along its length it is usually called a ruler.

METROLOGY AND INSTRUMENTATION (M602) -MODULE 2 True straightness can in some cases be checked by using a laser line level as an optical straightedge: it can illuminate an accurately straight line on a flat surface such as the edge of a plank or shelf. It is possible to do all compass and straightedge constructions without the straightedge. That is, it is possible, using only a compass, to find the intersection of two lines given two points on each, and to find the tangent points to circles. It is not, however, possible to do all constructions using only a straightedge. It is possible to do them with straightedge alone given one circle and its center.

Flatnes Testing &Squareness Testing

Flatness is tes ted by using angle plates,Surface plates,V Blocks ,Knife Edges Squareness is tested by engineers square,indicator method,Autocollimator Method etc.

ANGULAR MEASUREMENTS Sine bar

A sine bar is a tool used to measure angles in metalworking.

10" and 100mm Sine bars It consists of a hardened, precision ground body with two precision ground cylinders fixed at the ends. The distance between the centers of the cylinders is precisely controlled, and the top

METROLOGY AND INSTRUMENTATION (M602) -MODULE 2 of the bar is parallel to a line through the centers of the two rollers. The dimension between the two rollers is chosen to be a whole number (for ease of later calculations) and forms the hypotenuse of a triangle when in use. The image shows a 10 inch and a 100 mm sine bar, however, in the U.S., 5 inch sine bars are the most commonly used. When a sine bar is placed on a level surface the top edge will be parallel to that surface. If one roller is raised by a known distance, usually using gauge blocks, then the top edge of the bar will be tilted by the same amount forming an angle that may be calculated by the...

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