Metrology, Machines and Mechanisms Flashcards

Flashcards generated from lecture notes on Metrology, Machines and Mechanisms.

Why is it practically impossible to achieve the exact nominal measurement when manufacturing a part?

Due to factors such as the instrument's precision, environmental conditions, and operator skill.

Why is temperature important in precision measurements?

Because metals expand with temperature, and corrections are needed relative to a base temperature.

What is required in addition to the nominal dimension (N) to define a tolerance?

The IT (interval of tolerance) value, which depends on N.

What must be known to define a dimension with ISA norms?

Whether it's a hole-based or shaft-based system.

How are seat or adjustment classes designated?

By letters of the alphabet followed by a number.

What is the formula to establish the limits (tolerances) that correspond to each quality?

i = 0.45√𝑁 + 0.001N

In what unit is 'i' expressed in the ISA tolerance formula?

Microns (μ).

In what unit is 'N' expressed in the ISA tolerance formula?

Millimeters (mm).

For what types of manufacturing are IT numbers 1 to 4 used?

Extra-precise adjustments (measuring instruments).

For what types of manufacturing are IT numbers 5 to 11 used?

Precise adjustments, covering normal mechanical couplings.

For what types of manufacturing are IT numbers 12 to 16 used?

Parts not directly coupled after manufacturing, like those made by milling, rolling, or stamping.

What does a lower IT number imply about manufacturing quality?

Higher manufacturing quality is required.

What does SAU stand for?

Sistema de Agujero Único (Hole-Based System)

What does SEU stand for?

Sistema de Eje Único (Shaft-Based System)

What is the base element in the hole-based system (SAU)?

The hole, common to all shafts manufactured.

In the hole-based system, what value coincides with the nominal size (N)?

The minimum size of the hole, meaning the lower deviation is 0.

In the shaft-based system, are the tolerances for the shaft positive or negative?

Negative; the real measurement can be smaller but never larger than the nominal.

What do uppercase letters A to G represent in the ISA system for holes?

Clearances or games.

What letter represents sliding fit for holes and shafts in the ISA system?

H for holes, h for shafts

What do lowercase letters a to g represent in the ISA system for shafts?

Clearances or games.

In the hole-based system, with limits for H7 at 0.35 and j6 at -9.13, what is the likely fit?

An interference fit, or uncertain, since the tolerances leave little margin.

What is the purpose of knowing tolerance ranges like 80-100 mm?

To consult a table and see what tolerance margins IT provides for that range.

What is meant by 'ajuste' or fit?

The assembly of two parts in relation to the service or dependence between them.

What are the three classes of fits?

Free or loose, interference or press fit and sliding.

What is 'i' in the context of ISA tolerances?

A 'unit of tolerance' according to ISA norms.

What is a dimensional tolerance?

The variation around the ideal value, within acceptable limits to maintain quality and interchangeability.

How is the value of a specific quality obtained in the ISA norms?

From an ISA table that cross-references dimension ranges and IT values.

What fit does 55 m6 represent and in which system is it expressed?

A shaft-based system (SEU).

What fit does 30D8 represent and in which system is it expressed?

A hole-based system (SAU).

In the hole-based system, what signifies the position relative to the zero line?

The nominal measurement coincides with the minimum measurement of the hole

In the shaft-based system, how are different fits symbolized?

Lowercase letters: 'a' to 'g' for free fits, 'h' for sliding, and 'i' to 'z' for interference or press fits.

What are the main parts of a micrometer?

Frame, fixed scale, moving scale (drum), and spindle.

What does the frame of a micrometer need to provide?

Long-term stability, high rigidity, and lightweight.

How is the appreciation (resolution) of a micrometer defined?

The smallest division of the fixed scale divided by the number of divisions on the moving scale.

What does a comparator do?

Compares measurements, indicating if they fall within a certain range.

What is the general appreciation (resolution) of a comparator?

0. 01mm (each division corresponding to 0.01mm).

Is a comparator a type of direct or indirect instrument?

Indirect

What instrument would you use to measure a 20 +/- 0.5 mm hole?

Calipers.

What instrument would you use to measure a 26 +/- 0.1 mm shaft?

Calipers.

What instrument would you use to measure roundness in a shaft +/- 0.01 mm?

Micrometer.

What instrument would you use to measure the thickness of aluminum foil?

Comparator.

What are the primary angles of a single-point cutting tool?

Clearance angle (alpha), edge or wedge angle (beta), rake or chip angle (gamma), cutting angle (beta + alpha).

What are the characteristics desirable in cutting tools?

Hardness, toughness, chemical stability, and thermal resistance.

What does the formula G = Q . V . g . 60 / 1000 calculate?

Weight (in kg) of chips produced per hour.

What is the main movement in a lathe?

Continuous rotation of the material being machined.

What are some of the operations that can be performed on a lathe?

Cylindrical turning, threading, facing.

A) What are at least 4 machining operations feasible on a parallel lathe?

Spotting, drilling, end-facing, cutting off, revolution grooving.

B) What position does the carriage or 'charriot' occupy on a lathe, and what is its purpose?

The charriot is positioned longitudinally and advances transversely to perform operations. It is used for all types of revolution operations such as turning, cones, grooving, facing, cut-off and threads.

Why is continuous variable speed advantageous in a machine tool?

For threading, it allows varying feed speed for different thread pitches. It also maintains the cutting speed while advancing with the carriage.

What parameters are considered when calculating power in a horizontal parallel lathe?

Chip removal section (q), specific cutting force (Ks), feed rate (Vc), and machine efficiency (N).

List and describe the steps for threading on a lathe.

Calculations, tool grinding, part preparation, tool positioning, speed setting, thread pitch setting, approach cutting, pitch verification, and successive passes.

What types of pieces can be made on a lathe?

Typical section cut: central guides for tailstock, external guides for longitudinal carriage. Turning railway shafts, shafts, nuts.

Describe the function and working method of a slotting machine?

It is a machine tool used for making grooves, notches, and operations by means of a reciprocating linear motion of a tool over fixed pieces.

Describe a broaching machine.

It is a machine that linearly removes material in a progressive way, using the ordered succession of cutting edges (internal or external) by mechanical or hydraulic action.

Describe the key features of a centerless grinder.

Centerless grinding, used for short parts of simple shape, uses two wheels and a work rest blade instead of centers to support and rotate the workpiece

Describe the components and working process of a honing machine?

The machine is used for raising the precision and surface quality with abrasive stones also the macro geometry

How are milling machines classified?

According to the position of the spindle axis: horizontal, vertical, and universal (both horizontal and vertical).

Describe the working of a horizontal milling machine?

A cutter supported at both ends of an arbor is rotated and the work piece is fed into the cutter

Describe the working of a vertical milling machine?

The spindle axis is vertical, and the cutter is mounted on the spindle and rotates about its axis.

Describe what defines a universal milling machine?

Workpiece table adjustable relative to the spindle axis, capability to mount accessories for vertical or inclined milling, and the ability to use a universal dividing head and tailstock.

What is a mechanism?

A set of mechanical components that receive a specified movement or energy and transform it into a movement with distinct kinematic characteristics

What is a kinematic chain?

It is a collection of links and joints capable of relative motion.

What are transforming elements?

Mechanisms that change the type of motion in a machine: rack and pinion, screw-nut, cam and eccentric, connecting rod-crank-piston, ratchet, free wheel.

What are auxiliary elements?

Mechanisms that do not serve a specific function but facilitate the machine's operation: energy accumulators, energy dissipaters, clutches, and other elements such as supports and bearings.

How do mechanisms modify input force?

They are used to lift a large weight with a small force.

What is the Grashof criterion?

A condition determining the rotatability of links in a four-bar linkage based on link lengths.

What is degree of freedom?

It's the number of independent parameters needed to uniquly define position in space at any moment.

What is constant in mechanical transmissions when operating in uniform mode?

Input Rotation speed

What mechanical devices connect components transmitting kinetic energy?

Couplings

What type of coupling transmits high levels of torque?

Rigid coupling

What determines the selection of a coupling?

Characteristics of the application

What are brakes and clutches?

Mechanical or magnetic devices for connection between two machine elements

How are flexible transmission components utilized?

Used when great power is needed over longer distances

What are types of flexible transmission components?

Cables, chains, and pulleys

Where are cables preferred transmission choices?

Used instead of chains because they are better over very long distances

Where are chains utilized?

Efficient means to transmit kinetic energy in industrial purposes

Give a comparison of belts and chain operations?

Chain belts wear over time as compared to chain belts

What must occur for power transmission in chain belts?

Must rely upon friction with the belt and pulleys

Give four steps needed for belt-transmission?

Component integrity, power, alignment and tension

Given belt transmission, why is tension needed?

So that belts won't slip

What is the negative defect of belts transmitting energy?

There can a synching loss

What is the main advantage of using mechanical belts?

They are cost effective

A) What do bearings do?

Support a machine component that allows kinetic motion to function correctly, reduce friction

B) What characteristics are desirable for bearings?

Discharge force, reduce friction loss, heat dissipation and mechanical wear component

List the four elements to all bearings?

Roller , race inner, race outer and cage

Where are the load surfaces in bearings?

Inner and outer rings

Why do wheels roll instead of rub?

To reduce wear and friction

Bearings; what is the impact of ball size utilized?

The larger the loads the larger ball sizes, and vice versa

What is the basic way to relate load with bearing life?

Load is inverse function of life

Lubrication; when is grease preferable?

Good for heat absorption and noise

Lubrication; when is oil preferable?

Good heat absorption and particulate contamination removal

What is the function of bearing cage?

Holds its parts, less wear and friction for elements

Where does damage occur in a bearing?

load bearing point

Function and properties of gears?

Cylinders with tooth contours to transmit rotation via pressure applied by gear teeth.

Basic gear classifications and their orientations?

direct action and indirect action

What properties of gear teeth need most inspection

Diameter and thickness properties

In metric systems what is needed so gears are interchangeable and mass produced?

Ratio of circumference to number of teeth

What part of a gear needs lubrication?

teeth

What aspect of gearing limits power?

Strength of Material

What is the purpose of gear chains?

The chain transmits kinetic energy over significant distances.