Mechanical Engineering Drawing MECH 211/M Lecture #10 SECTIONS-FASTERNERS- BEARINGS-SEALS Dr. John Cheung

Sections

Outline Sectional views More sectional views in one drawing Half sections Threads and Assemblies in section Offset section Ribs, hoes and lugs in section Revolved and removed section Phantom lines

Sectional Views FULL SECTION Shows interior detail Describes complicated parts Eliminates the need for hidden lines Frequently replaces a regular view FULL SECTION

Sectional Views Full Section A section view in which the cutting plane extends entirely through the object in a straight line

Sectional Views Sectional lining Also called crosshatching Indicates surface that has been theoretically cut Lining symbols may indicate the material that makes up the object

Sectional Views General Purpose Sectional lining Drawn with thin lines To look for Direction of section lines Space for accommodating dimensions Thin parts shown as thick lines Drawn with thin lines Lines are usually drawn at 45 to the object’s main outline The same angle and direction is used for the whole ”cut” surface of a part Large areas can be marked with section lining only around the outline

Two or more Sectional Views If two or more sections appear on the same drawing: Cutting-plane lines are identified by two identical capital letters Sectional view subtitles incorporate the identification letters. For clarity, should point to the right. Avoid hidden line in section view

Half Sections Shows one-half of the view in section Has two cutting planes perpendicular to each other One quarter of the object is removed Cutting line should continue

Threads in Sections Representation of threads in drawing Detailed, Schematic, Simplified

Assemblies in Sections Sectioning in assembly drawings Section lining on assembly drawings Shafts, Bolts, Pins, Keyseats No section

Assemblies in Sections Section lining in assembly drawings Use opposite directions for section lining on adjacent parts For more than two parts, use lining at a different angle

Assemblies in Sections Section lining in assembly drawings Avoid symbolic section lining on drawings to be microformed If adjacent thin parts are filled in, leave space between them

Assemblies in Sections Parts generally not sectioned: Shafts Bolts Pins Keyseats Similar solid parts A broken-out section of a shaft may be used to describe a key, keyseat, or pin.

Offset Sections A cutting plane can be bent to include several surfaces

Ribs, Holes, and Lugs in Sections Parts generally not sectioned: Conventions for aligning ribs, holes and lugs in section

Ribs, Holes, and Lugs in Sections Aligning and rotating When a true projection would be misleading, the rib, hole or lug is revolved to show its true relationship to the part Rib here

Revolved and removed Sections Ribs, spokes, and arms

Revolved and removed Sections Show cross-sectional shape of ribs, spokes, or arms Section is rotated 90 degrees

Revolved and removed Sections Revolved section: Section may be superimposed on regular view of part Regular view is broken if needed for clarity or to add dimensions Removed section: Removed to an open area on drawing; may be enlarged. Shorten object length.

Spokes and arms in Sections Section lining is not drawn on parts that are Not solid Not continuous around the hub

Partial or broken out Sections Partial sections are indicated with an irregular break line. A cutting-plane line is not required.

Phantom or Hidden Sections Used to show interior details of parts that are not symmetric, or mating parts in assembly A phantom section is a sectional view superimposed on a regular view The front portion of the object is not removed

Screws, Nuts and Bolts Used to assemble machine parts Used to transmit power / motion The threads are cut or rolled Bolts and nuts must be matched

Screw and Thread Terminology Major Diameter - The largest diameter of a screw thread. Minor Diameter - The smallest diameter of a screw thread. Pitch Pitch diameter

Tap and Die

Thread Specifications – Imperial System ANSI Y14.6 - 1998 Thread form Thread series Major diameter Class of fit Threads per inch

Screw Thread Forms Unified thread is agreed as standard in US, Canada and Britain, the crest may be flat or rounded but the root is rounded. Otherwise similar to American national

Screw Tread Forms ISO Metric is the most common of all. The depth is smaller than that of Unified National thread

Measuring Thread Pitch Pitch is the distance along the axis between corresponding points in adjacent threads (i.e crest to crest or root to root) Metric: Measured in millimeters (i.e. M10 X 1.5) Imperial: Measured in threads per inch Thread Pitch is measured with scale or a thread pitch gage

Thread Types Series: Varies with the pitch and the major diameter of the thread Coarse Series (UNC) General purpose usage Fine Series (UNF) Used when a great deal of force is necessary Extra Fine Series (UNEF) Used when the length of engagement is short and there is a high degree of stress 8-Pitch (8UN), 12-Pitch (12UN), 16-Pitch (16UN) Does not depend on the diameter

Metric Thread Series Simplified compared to Unified Series Only two series Coarse (General Purpose) Fine

Simplified & Schematic Internal Symbols Normal & Section Drawings

Imperial Thread Notes

Basic Metric Thread Note

Screws, Nuts and Bolts

Large variety of bolts (dimensional, head shape, etc.) Material, quality, finishing Grade

Fastener Locking

Fastener Locking Durlock nut Castellated nut Jam nut

Screw Types Head can have different shapes Pass through a clearance hole to screw into member Socket screws are used while in crowded condition

Non-Permanent Fasteners Snap Rings

Non-Permanent Fasteners Pins

Used to permanently fasten mechanical components

Common Riveted Joints

Blind Rivets

Welding Joining of two part using a third component – filler that joins the parts when in liquid state Soldering and brazing – low temperature binding materials – Sn-Pb, Cu-Ag alloys Limited capability to face thermo-mechanical loading

Welding Very well regulated activity It requires license to practice Welders bear significant responsibility The activity is based on rigorous rules and regulations Designer prescribe welding based on mechanics of materials calculations Symbols indicate the type of welding

Basic Welding Symbols

Compression Springs Extension Springs Torsion Springs Designed to store energy when deflected and return the same amount of energy when released Basically divided as Helical and Flat springs Helical springs are sub divided as Compression Springs Extension Springs Torsion Springs

Helical Springs Compression, Extension & Torsion

Spring Representation Detailed representation Schematic representation Working drawing of a compression spring

Gears

Gear Representation A table containing cutting data must accompany the representation

Ball Bearings

Ball and Roller Bearings

Antifriction Bearings Bearing Symbols Classified into simplified, pictorial and schematic representations Simplified representation – used when not necessary to show the form or size of the rolling bearings or details of their inner design (A) When it is desirable to show the functional principle of rolling elements, symbols for the appropriate rolling element and raceway surface are added (C)

Lubricants and Radial Seals Radial Positive Contact Seals Applies sealing pressure to mating cylindrical surface to retain fluids and to exclude foreign matter. Used for oscillating and reciprocating shaft motion.

Lubricants and Radial Seals Seal Symbols The simplified representation of seals (Fig. 21-5-12) recommended for use on drawings, wherever it is not needed to show the exact form and size of seals Fig, 21-5-13 Functional representation of seals