Chapter 13
Clearance hole
A hole slightly larger than the bolt or fastener that is intended to pass through it
fine thread
a greater number of threads per inch it is used extensively in automotive and aircraft construction.
lead
distance a screw thread advances axially in one turn
rivet symbols
trusses, solid black circles for feild rivets
regular key (2 kinds)
flat: key 1/4 width in diameter, or half of key is sunk in shaft square: tapered: 1/8th per foot top surface tapered
detailed
more exact, helical curves replaced by straight lines, realistic
machine pins
taper, light work fasten hubs or collar caps straight, dowel, cylindrical or conical for accurate alignment clevis,used in clevis held by cotter pins
external thread
thread on the outside of a shaft
pitch
A distance of uniform measure determined at a point on one unit to the same corresponding point on the next unit; used in threads, springs,and other machine parts.
woodruff key
A flat key, semicircular in shape. The two basic dimensions (diameter and width) are coded into the key number. The last two digits designate the diameter in 1/8ths of an inch. The preceding digits designate the width in 1/32nds of an inch
coarse thread
A general purpose thread used for holding.
Class A or B ; 1, 2, 3
A refers to external threads B refers to internal threads 1A and 1B have generous tolerances, rapid (de) assembly 2A and B in normal and general applications 3A &B highly accuracte and close fitting threads
single thread
Composed of one ridge therefore the lead is equal to the pitch (lead xpitch)
buttress thread
Designed to transmit power in one direction only. guns, jacks, high strength requirements
american national thread
Flattened roots and crests, is a stronger thread. This form replaced the sharp- V thread.
square thread
Is the theoretically the ideal thread for power transmission, since its face is nearly at right angles to the axis
compression springs
Offer resistance to a compressive force
extension springs
Offer resistance to a pulling force.
torsion springs
Offer resistance to a torque or twisting force.
Right Hand vs Left Hand threads
RH:clockwise; the default LH:counterclockwise; LH label designated in drawing
Pratt & Whitney Key
Rectangular with semi-cylindrical ends, 2/3 of its height is sunk into shaft keyseat
gib head key
Same as square taper or flat taper key except for that a Gib head allows for easy removal
metric thread
Standard screw thread agreed upon for international screw thread fasteners. M
depth of thread
The distance between crest and root measured normal to the axis.
form of thread
The cross section of thread cut by a plane containing the axis
pitch diameter
The diameter of an imaginary cylinder that is located equidistant between the major and minor diameters
major diameter
The largest diameter on an internal or external thread
minor diameter
The smallest diameter on an internal or external thread
series of thread
The standard number of threads per inch for various diameters.
side
The surface of the thread that connects the crest with the root
multiple threads
Threads composed of two or more ridges running side by side (pens, toothpaste caps,
UNEF
Unified Extra Fine thread series
sharp v thread
Useful for certain adjustments because of the increased friction resulting from the full thread face. 60 degrees
knuckle thread
Usually rolled from sheet metal but is sometimes cast.; bottle tops, globes, bulbs, sockets
screw thread
a ridge of uniform cross section in the form of a helix on the external or internal surface of a cylinder.
internal thread
a thread on the inside of a member, as in a hole.
8-pitch thread
all diameters have 8 threads per inch; bolts and high pressure fasterners/ pipes ; 8N
root
bottom surface joining two surfaces of a thread
schematic
common simplified, shorter thick parallel lines, ends chamfered
12 pitch thread
diameters have 12 threads per inch; thin nuts on shafts and sleeves for construction ; 12N
16 pitch thread
diameters have 16 threads per inch; fine thread neccessary regardless of diameter; collars and bearing retaining nuts; 16N
shop vs field rivets
driven in shop vs in the field
blind/pop rivets
fastening together thin sheet metals , hollow, center pin or rivet guns
class 2 fit
high quality of commercial thread product for great bulk of interchangeable screw thread work
class 3 fit
highest quality of of commerically thread product where cost of tools are warranted
acme thread
is a modification of the Square Thread and has largely replaced it. Stronger than the square thread. G (general purpose), C (centralizing)
Standard Worm Thread
is similar to the acme thread but is deeper.
small rivets
light work ; tinners, coppers and belt rivets
Whitworth Thread
old British standard thread; thread degree 55º
Class 1 fit
recommended for screw thread work where clearance between mating parts is essential for rapid assembly
feather key
rectangular to prevent rotary motion, but permits relative longitudinal motion
three methods for thread drawing
schematic, simplified detailed
angle of thread
the angle between the sides of the thread measured in a plane through the axis of the screw.
axis of screw
the longitudinal center-line through the screw
unified thread
the standard thread agreed upon by the United States, Canada, and Great Britain.
crest
top surface joining the two sides of a thread
ssimplified
uses hidden lines to represent thread depth
