DRILLING

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DRILLING

• Internal and cylindrical surfaces and holes are
  produced more than any other shape. These
  surfaces made by drilling operation.
• Drilling operation is relatively easy but there
  are some diffuculties in obtaining accuracy and
  precision due to
• chip formation inside the drilled hole
• diffuculty in cooling the inner surfaces
• lubrication diffuculty of the inner surfaces
• Drilling is done by using drill bits

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TYPES OF DRILL BITS

• Twist drills
• - Normally made of HSS and sharpened by grinding
• - End-cutting tools used to produce holes in most
  types of material
• - Twist drill parts
• 1. Shank straight (usually held in a drill
  chuck) or tapered-shank (fit into the internal
  taper of the drill press spindle)
• 2. Body flutes (two or more helical groove
  forms cutting edges, admit cutting fluid allow
  chips to escape), margin (narrow, raised section
  on the body of the drill, provide a full size to
  the drill body and cutting edges), body clearance
  (undercut portion of the body, reduce friction
  between the drill and the hole during the
  drilling operation), web (thin partition in the
  center of the drill that extends the full length
  of the flute)

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TYPES OF DRILL BITS(cont.)

• 3. Point consists of chisel edge (dead center),
  cutting edge or lip, lip clearance (the relief
  ground on the point of the drill extending from
  the cutting edge back to the heel), and heel
• - Drill point characteristics efficient drilling
  of the wide variety of materials used by industry
  requires a great variety of drill points the
  most important factors determining the size of
  the drilled hole are the characteristics of the
  drill point the use of various point angles and
  lip clearances have the following effects

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TYPES OF DRILL BITS(cont.)

• 1. Control the size, quality, and straightness of
  the drilled holes
• 2. Control the size, shape, and formation of the
  chip
• 3. Control the chip flow up the flutes
• 4. Increase or decrease the strength of the
  cutting edges
• 5. Affect the wear rates at the cutting edges
• 6. Control the amount of drilling pressure
  required
• 7. Control the amount of burr produced
• 8. Affect the amount of heat generated
• 9. Permit the use of various speeds and feeds

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TYPES OF DRILL BITS

• - Drill point angles and clearance
• 1. Conventional point (118) most commonly used
  general purpose drilling lip clearance angle is
  between 8 to 12.
• 2. Long angle point (60 to 90) used for the
  drilling of nonferrous metals, soft cast irons,
  plastics, fibers, and wood lip clearance angle
  is large (12 to 15).

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TYPES OF DRILL BITS

• 3. Flat angle point (135 to 150o) for hard and
  tough materials shorter cutting edge tends to
  reduce the friction and heat generated during
  drilling lip clearance angle (6 to 8o) is small
  to provide as much
• support as possible for the drilling edges
• Note
• Too much lip clearance weakens the cutting
  edges due to the lack of support behind the
  cutting edges causes the drill to chip and break
  easily quick dulling and poor tool life

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TYPES OF DRILL BITS

• Too little lip clearance results in the use of
  heavy drilling pressure, which causes the cutting
  edges to wear quickly because of the excessive
  heat generated and also places undue strain on
  the drill
• and equipment poor holes and drill breakage
• Drilling facts and problems
• 1. The length of both cutting edges must be the
  same. Unequal edge length will force the drill
  point off center, causing one edge to do more
  cutting than the other and produce an oversize
  hole.

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TYPES OF DRILL BITS

• 2. The angle of both lips (cutting edges) should
  be the same. If the angles are unequal, the drill
  will cut an oversize hole.
• 3. Cutting edges should be free from nicks or
  wear.
• 4. There should be no sign of wear on the margin.
•  Other types of drills
• 1. Low helix drills used for soft materials
  (brass, Al) and thin materials, used to drill
  shallow holes, can remove the large volume of
  chips formed by high rates of production
• 2. High helix drills used to drill deep holes in
  Al, copper, die-cast material, and other metals
  where the chips have a tendency to jam in a hole,
  high helix angle and wider flutes assist in
  clearing chips from the holes

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TYPES OF DRILL BITS

• 3. Core drills
• 4. Oil hole drills
• 5. Straight-fluted drills used for soft
  materials and plastics, straight flute prevents
  the drill from drawing itself into the material
  (digging in) while cutting
• 6. Deep hole or gun drills
• 7. Spade drills
• 8. Step drills used to drill and countersink or
  drill and counter bore different sizes of holes
  in one operation
• 9. Saw-type hole cutters

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Twist Drill
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Spade Drill
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Step Drill
Gun Drill
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Operations Related To Drilling

• Reaming(Raybalamak)
• Used to slightly enlarge a hole to provide a
  better tolerance on its diameter and to improve
  its surface finish
• Tapping(Yiv çekmek, dis açmak)
• Performed by a tap, used to provide internal
  screw threads on an existing hole
• Contourboring(Kademe)
• Used to seat bolt heads

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• Countersinking(Havsa)
• Similar to counterbore but it is cone shaped
• Centering(Punta)
• Also called center drilling. The tool is also
  called as center drill. Used to start the
  subsequent drilling accurately
• Spotfacing
• Similar to milling operation, provides flat
  working surface on the workpart

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DRILL PRESSES

• Upright drill
• -stands on the floor
• - consists of a table, drilling head, base and
  column for support
• Bench drill
• - similar to upright but smaller
• - used to drill small diameter holes
• - instead of standing on floor, it is mounted on
  a table
• Radial drill
• - large drill press
• -used to cut holes in large parts
• -head can be adjusted along arm

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Upright Drill Press
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Bench Drill
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Radial Drill
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DRILL PRESSES

• Gang drill
• - series of 2-6 upright drills connected in line
  arrangement
• - each spindle powered and operated
  independently but share common work-table
• -used in high production rate operations
• Numerically controlled drill presses

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Gang Drill
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• Workholding
• VISE
• General workholding device, has two jaws that
  grasp the work in position.
• FIXURES
• Another workholding device, usually custom made
  for the particular workpart.
• JIG (Drill Jig)
• This one is also designed for the workpart. Main
  difference between jig and fixure is that jig
  provides a guidance but fixure does not.

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Vise
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Fixtures
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Drill Jig
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• Cutting Conditions In Drilling
• ?
• N
• p D
• N rotational speed, rev/min
• ? cutting speed, in/min (mm/min)
• D drill diameter, in (mm)
• f feed, in/rev (mm/rev). Recommended feeds are
  roughly proportional to drill diameter, higher
  feeds are used with large diameters.
• fr feed rate, in/min (mm/min)
• fr N.f
• MRRmaterial removal rate ¼( ?.D2. fr )
• (valid only after the drill reaches full diameter)

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• Tmdrilling time, min.
• There are two types of drilled holes
• Through hole
• tA
• Tm
• fr
• t work thickness, in (mm)
• A approach allowance, in (mm)
• A0.5 D tan (90-½ ?)
• ? drill point angle
• Blind hole
• d
• Tm
• fr
• d hole depth