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Drill Dissection

Drill Dissection. What’s so interesting about a drill? It’s 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) . Major Drill Components.

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Drill Dissection

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  1. Drill Dissection What’s so interesting about a drill? It’s 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 Stationary Windings (stator) Commutator 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 Brushes (2) Armature (rotating unit) Internal view of the “Universal” motor used in the SKIL electric hand drill

  13. 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 (Tesla’s 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

  15. Universal Motor - AC and DC

  16. 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 S N B I = current Coil (single conductor shown) Build your own motor: http://www.exploratorium.edu/snacks/snackintro.html

  17. How does a chuck work? Source: Macaulay, D., 1998, The New Way Things Work, Houghton Mifflin Company, Boston, MA.

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