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Industrial Skills

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Nuts and Washers Nuts have coarse or fine internal threads that correspond to the threads of a bolt and are designed to screw onto the bolt to fasten it in place. – PowerPoint PPT presentation

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Title: Industrial Skills


1
Industrial Skills
  • Fasteners

2
Fasteners are used in manufactured products for
several basic purposes
  • They simplify manufacture.
  • They simplify repairs.
  • They provide safety.

3
When selecting a fastener for a particular use,
consider these factors
  • Strength Will it hold the loads and pressures?
  • Security Will it remain attached?
  • Cost Realistic?
  • Installation Appropriate for situation?
  • Skill Is specialized training needed?
  • Equipment Is specialized equipment needed and
    available?
  • Appearance If the fastener shows, which kind
    looks best?

4
Nails Most common method of fastening one
wooden member to another.
  • Simplest quickest.
  • May not result in the strongest of joints.
  • Many different sizes and various shapes of heads,
    points shanks.
  • Each type designed for a particular purpose.
  • Drive nails at angles slanting toward or away
    from each other to get best holding power.

Nails are designated by penny
size, originally a term which related to
price per hundred but now signifies length. The
symbol for penny is the lowercase letter d.
Nail diameter increases with length. Nails are
now sold by the pound.
5
Screws A large and important family of
fasteners.
Mechanical devices for fastening things
together. Essentially a cylindrical or conical
piece of metal threaded evenly around its outside
surface with an advancing spiral ridge and
commonly having a slotted head it penetrates
only by being turned, as with a screwdriver.
  • The most common types of screws are
  • Sheet-metal screws
  • Wood screws
  • Machine screws
  • Set screws

Use Categories
6
Wood Screws
  • Serve much the same purpose as a nail, but
  • Provide greater holding power than a nail.
  • Screws can be easily removed and replaced.
  • Screws are neater in appearance and offer more
    decorative possibilities.
  • In addition to fastening pieces of wood together
    the most common use of wood screws would be to
    anchor objects (hardware) to a wood surface.

7
Sheet-Metal Screws
  • Also called Tapping Screws or Self-Threading
    Screws.
  • Used to fasten light pieces of metal together or
    to attach covers, panels and other light parts.
  • These screws have sharp threads that can cut
    their own grooves into metal.
  • They come with coarse or fine threads and are
    usually case hardened to cut threads and
    withstand hard twisting forces.
  • Distinguishable from wood screws in that they are
    threaded all the way from the point to the head.

8
Machine Screws
  • Used for the assembly of metal parts and usually
    are driven into threaded holes rather than
    drawn tight with nuts.
  • Like all screws, there are many head designs to
    choose from.
  • Machine screw threads are also designated by the
    number of threads per inch, just like bolt
    threads
  • A 6-32 machine screw has a 6 body diameter and
    32 threads per inch of length.
  • Most machine screws are fully threaded to the
    head.

9
Set Screws
  • Frequently used to hold a knob, collar, pulley or
    gear to a rotating shaft.
  • There are a variety of head or point styles,
    each best suited for its job.
  • Generally made of high-strength material and are
    heat treated.
  • Not an especially strong type of fastening
    depend on friction and shear to hold parts
    together.

10
Once you have decided to use screws, in addition
to the use category, you must consider four
things before ordering.
  • Type of head
  • Material made of
  • The length
  • The diameter

11
The type of head should include both the
shape and the style.
Screw Head Shapes
Screw Head Styles
Pan Head
Flanged Hex Head
Truss Head
Hex Head
12
The most common material screws are made of is
steel.
  • If the fastener is exposed to the weather
    steel alone does not offer much protection
    against the harmful effects of corrosion.
  • Coatings offer more protection.
  • Steel Blued
  • Zinc Coated
  • Chromium
  • Galvanized
  • Nickel
  • Silver Plate
  • Gold Plate
  • Marine Applications may require different metals
    and/or materials.
  • Stainless Steel
  • Aluminum
  • Copper
  • Brass
  • Bronze
  • Synthetic Materials (Plastic or Nylon)

13
The length of screws commonly range from ¼
inch to 4 inches. Shorter or longer lengths are
generally special order items. (Metric lengths
are also available)
14
Screw diameters can be expressed by the gauge
number or by the fraction of an inch. (Metric
diameters are expressed in mm)
15
American Screw Gauge
  • Sizes are designated by length in inches
    (millimeters).
  • Diameters less than ¼ inch (6 mm) use gauge
    number.
  • Diameters greater than ¼ inch use fractions of
    an inch.
  • Wood screws are an exception to this rule in
    that they generally go up to a 20 gauge (21/64).

16
Bolts, Cap Screws, Nuts Washers
  • Nomenclature of bolt-type fasteners tends to be
    confusing.
  • Bolts are usually used in plain holes drilled
    through the parts being fastened.
  • Bolts are generally held in place with a mating
    nut.
  • When the nut for any bolt is turned down on wood,
    always use a flat washer under the nut.
  • Cap screws are normally used in threaded holes,
    without a nut.

17
Machine Bolts/Cap Screws
  • Machine bolts have square or hexagonal heads.
  • Installed with a wrench.
  • Usually used if the parts to be joined are made
    of metal.
  • Cap screws generally look just like a machine
    bolt.
  • Slightly different application.
  • Screwed into threaded holes rather than being
    used with a nut.

18
Round-Head Bolts
  • Commonly used to fasten wood parts.
  • Most have a square neck under the head.
  • Also used to fasten steel parts with square
    punched holes.
  • A Carriage Bolt is the most common type of
    round-headed bolt to be used when working with
    wood.
  • A Plow Bolt has a flat, tapered head that fits
    into a countersunk hole primarily used with
    metal parts.
  • Used in the marine industry for attaching cutters
    and other parts to dredges.

Plow Bolt
Carriage Bolts
19
  • Stove Bolts are available with the same types of
    head designs as wood screws, in diameters from
    5/32 to 1/2 and in lengths from 3/8 to 6
    inches.
  • Studs are another type of threaded fastener,
    which have no head at all and is merely a steel
    rod with threads on both ends.
  • One end is screwed into a part, other parts are
    assembled over the studs and screwed in place
    with a nut.

20
Other Bolts
  • Some fasteners are referred to as bolts but are
    actually screws.
  • A Lag Bolt is really a heavy-duty screw with a
    square or hex head.
  • Designed to be driven with a wrench.
  • Available in lengths from 1 to 6 and diameters
    from 1/4 to 1/2.
  • A Hanger Bolt is a fastener that has wood screw
    style threads on one end and machine threads on
    the other.
  • No head on this type of bolt.
  • Designed to be a hidden fastener.

21
Sizes and Descriptions
  • Threads External helical ribs on the body of a
    bolt at the end opposite the head.
  • The diameter of a bolt is determined by the
    diameter of the crest of the threads.
  • The length of most bolts (or machine screws) is
    determined by the measuring from the bottom of
    the head to the end of the threads.
  • Flat head bolts are measured from the threaded
    end to the top of the head.
  • The Head Size determines what size wrench or
    socket must be used to turn or hold the bolt or
    nut.
  • A square or hexagonal bolt head is measured
    across the flats.
  • Example A ¾ wrench is needed to turn a ½
    diameter bolt head.

22
Threads
  • Threads External helical ribs on the body of a
    bolt. Usually a bolt mates with internal
    threads of a nut.
  • The top of the rib is called the crest, or thread
    tip.
  • Bottom of the groove is called the thread root.
  • Threads are measured by counting the number per
    inch. (Metric threads are measured by the
    distance between threads pitch in mm)

Thread gauges are available that match threads
against those on the gauge.
23
  • The type of threads that are used for most
    applications are coarse with deep grooves.
  • Some threads are finer, with shallower grooves.
  • Bolts with fine threads are used only under
    special conditions such as when the parts being
    fastened have thin walls.
  • Bolts and screws normally have right-hand
    threads.
  • Turned to the right (clockwise) when tightened.
  • Occasionally, bolts, screws and nuts with
    left-hand threads are needed.
  • Turned to the left (counter-clockwise) when
    tightened.

24
American National Standards Institute( ANSI )
  • There are carefully controlled standards for
    threading bolts and nuts.
  • ANSI establishes such things as the angle of
    threads, the depth of the root and the
    manufacturing tolerances (fit) which are referred
    to as the Unified Screw Thread Standards.

25
International Organization for Standardization(
ISO )
  • Established standards for classifying metric
    bolts and screws.

26
  • Grades and Head Markings Inch-Series
  • The kind of steel bolts and screws are made of
    and the treatment they receive during manufacture
    determine their strength.
  • The Society of Automotive Engineers (SAE) has
    established standards for classifying inch-series
    bolts and screws into grades, based on their
    tensile strength.
  • Markings consist of radial slashes.
  • High-quality inch-series bolts and screws ¼ and
    larger have them.
  • Grade 5 or better hardware should be used in most
    situations.

27
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28
  • Grades and Head Markings - Metric
  • The kind of steel bolts and screws are made of
    and the treatment they receive during manufacture
    determine their strength.
  • The International Organization for
    Standardization (ISO) has established standards
    for classifying metric bolts and screws into
    property classes based on strength.
  • Numbers on the head indicate property class.
  • High-quality metric bolts and screws 4mm and
    larger have them.
  • Class 8.8 or better hardware should be used in
    most situations.

29
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30
Nuts and Washers
  • Nuts have coarse or fine internal threads that
    correspond to the threads of a bolt and are
    designed to screw onto the bolt to fasten it in
    place.
  • A great variety of shapes and sizes for standard
    and special applications.
  • Threads per inch or distance between threads can
    be determined with a thread gauge just like bolt
    threads.
  • Nuts have three important dimensions
  • Thickness
  • Distance across the flats
  • Inside diameter (same as that of the bolt with
    which it is to be used).

31
  • Hex and Square Nuts
  • The most common nuts, generally made of steel and
    are hexagonal or square in shape.
  • Jam Nuts Used to lock a threaded part in place.
  • Castellated and Slotted Nuts Secure a nut in
    place so it cant possibly come loose.
  • Self-Locking Nuts Stay firmly in place even
    with constant vibration.
  • Many other types of nuts available for special
    uses.

32
  • A plain washer is simply a steel disk with a hole
    through the center.
  • Like bolts and nuts the may be manufactured with
    a variety of different materials
  • They help distribute the load over an area larger
    than the head of the bolt or nut, thus reducing
    the stresses that would otherwise exist.
  • Plain washers are identified by their outside
    diameter and the diameter of the hole, which is
    the bolt size rather than the actual diameter of
    the hole.
  • The washer thickness varies with the size of the
    washer.

33
  • Lock washers are frequently used to keep nuts and
    bolts tight, especially when they are subject to
    vibration.
  • Helical Spring Washers Made of tough spring
    steel. They are split and one end of the split is
    bent up. When the nut is tightened, the section
    of the washer that is bent up bites into the
    nut and the fastened part.
  • Toothed Lock Washers Has many sharp,
    heat-treated teeth to dig into the surfaces
    pressing against it.
  • Many other types of washers are available for
    special uses.
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