Drill Dissection

1
Drill Dissection

• Whats so interesting about a drill? Its got
  lots of good stuff in it - electric motors,
  gears, bearings, etc
• It is a good example of an electro-mechanical
  power transmission system, and it is also an
  example of a machine tool (it drills holes)

2
Major Drill Components
Gears (Transmission)
Electric Motor
Chuck
Brushes
Handle
Bearings
Trigger Switch
3
Bearings Two Common Types

• Bushings - simple, cheap, limited life, porous
  material such as Oilite which holds oil like a
  sponge
• Rolling Element support axial or radial
  loading, long life, grease or oil-filled, various
  types of seals, readily available from standard
  product catalogs, ex. ball bearings

4
Roller Bearings
Tapered Roller
Spherical Roller
Needle
Roller
5
Rolling Element Bearing Parts
Outer Race
Inner Race
The parts and nomenclature for a Ball Bearing
Bore
Ball
Cage or Separator
6
Bearings -continued

• Hydrodynamic or Sleeve - oil filled, no wear,
  radial or thrust, common in automobile engines
  (e.g., crankshaft bearings)

Rotating Shaft
Sleeve Bearing
Shaft Rides On Oil Wedge
Oil Filled Cavity
A typical radial clearance is on the order of
.010
7
Types of Gears
Parallel Axis Gearing
A - Spur gears, external contact B - Spur gears,
internal contact C - Spur, Rack and pinion D -
Spur, Helical gears E - Herringbone F - Pin gear
ref. 4
8
Types of Gears - continued
Non-parallel or non-intersecting axis gearing
G - Bevel gears H - Spiral bevel J - Crown
bevel K - Spiral gears L - Worm and wheel M -
Hypoid gear
ref. 4
9
Gears - continued
a -Epicyclic train the gear wheel C is fixed
and the arm D moves around its axis at A, the
wheel B will have a retrograde motion and the
wheel A a faster motion in the direction of the
moving arm if the wheel A is fixed, B and C
will have unequal forward motions. b -Sun and
planet gear on a winch. c -Planetary motion as
applied to an apple-paring machine.
(a)
(b)
A
B
D
G
C
A
(c)
(d)
d -Epicyclic bevel gears an arm FG is fast on a
shaft AA bevel wheel B is loose on this arm
bevel wheels D and C are loose on the shaft AA
differential motions of the arm FG around and
with shaft A , or, by making the arm loose on
the shaft, a differential motion of the shaft and
arm can be obtained.
ref. 4
10
Gear Transmissions
Planet gears (4)
Ring Gear (can be stationary)
Sun Gear
Planetary Gearboxes - give high reduction
(between sun gear and planet carrier), compact
size, can distribute or add power
Planet Carrier
11
Gear Transmissions
Output Shaft
Two Stage, parallel shaft, helical gearset -
from the SKIL electric drill
Ball Bearing
Bushing
Input Pinion
12
Electric Motors

• AC - most common type for power applications,
  simple, cheap, constant speed operation
• DC - easily controlled, variable speed operation,
  with or without brushes, also function as
  generator

Stationary Windings (stator)
Commutator
Brushes (2)
Armature (rotating unit)
Internal view of the Universal motor used in
the SKIL electric hand drill
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General Types of Electric Motors

• Permanent Magnet DC
• Permanent magnet used in stationary field, rotor
  (armature) consists of windings, switching
  magnetic polarity to keep the motor turning,
  brushes make contact with commutator only runs
  on DC and speed is proportional to input voltage
• Brushless DC
• Magnets are in the rotor, windings in the stator,
  polarity switching of the windings is done
  externally by additional circuitry, no brushes to
  wear out, no sparking or electrical noise only
  run on DC speed proportional to input voltage

14
General Types of Electric Motors

• Universal motor
• Same as a permanent magnet except wound coils
  (electro-magnet) replace the stationary permanent
  magnet they will run on AC or DC and are most
  commonly found in electrical appliances as they
  are cheap and easy to vary speed
• AC Induction motor (Teslas genius)
• Wound coils in the stator, rotor has no magnets
  or coils, just a stack of steel laminations,
  speed is proportional to frequency of AC, making
  it difficult to vary speed of the motor

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Universal Motor - AC and DC
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Permanent Magnet DC Motor Operation

• Force generated F (I x B) L
• B magnetic flux density
• I current in wire
• L length of conductor

-
Commutator (rotates with coil)
F force
I
Brush
F
B magnetic field
Permanent Magnet
Permanent Magnet
L
N
S
B
I current
Coil (single conductor shown)
Build your own motor http//www.exploratorium.ed
u/snacks/snackintro.html
17
How does a chuck work?

• Source Macaulay, D., 1998, The New Way Things
  Work, Houghton Mifflin Company, Boston, MA.