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ADVANCED MECHANICAL DRAFTING

ADVANCED MECHANICAL DRAFTING. LECTURE #3. DRILLED. REAMED. BORED. Common Hole Types. COUNTERBORED. SPOTFACED. COUNTERSUNK. Ø.250 (1/4) THRU or Ø.250 (1/4)  .50. DRILLING. Drill size chart. Specifying drilled holes on drawings. Drill names. CLEARANCE HOLES.

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ADVANCED MECHANICAL DRAFTING

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  1. ADVANCED MECHANICAL DRAFTING LECTURE #3

  2. DRILLED REAMED BORED Common Hole Types COUNTERBORED SPOTFACED COUNTERSUNK

  3. Ø.250 (1/4) THRU or Ø.250 (1/4)  .50 DRILLING • Drill size chart • Specifying drilled holes on drawings • Drill names

  4. CLEARANCE HOLES • Used for holes that accommodate fasteners (usually screws) • Must be larger diameter than the screw for a clearance fit • Must be THRU holes • Tapping section of MHB contains necessary data

  5. USE “FREE FIT” CLEARANCE HOLES UNLESS OTHERWISE SPECIFIED Ø.397 (X) THRU CLEARANCE HOLES EXAMPLE: Specify clearance hole for 3/8” screw on the drawing.

  6. GSSP FASTENERS ¼” SOCKET HEAD CAP SCREW & ¼” MEDIUM LOCK WASHER

  7. SOCKET HEAD CAP SCREW

  8. LOCK WASHER

  9. FIRST NOTE LINE SECOND NOTE LINE COUNTERBORELOCATIONS and SIZES • Required location data • Number of hole locations • Diameter of bolt circle • Angle between holes • Required size data • Number of holes • Drill size and depth • Counterbore diameter and depth

  10. ROUNDING DECIMAL DIMENSIONS Dimensions are normally rounded to two (2) places (hundredths), but may be rounded to three or four places if tighter tolerances are required or if dimension corresponds to a tool size • Rounding Rules • Round digits > 5UP  • Round digits < 5DOWN  • Round 5UP if previous digit is ODD • Round 5DOWN if previous digit is EVEN • Examples: • .625 (5/8)  .62 .875 (7/8)  .88 • .3125 (5/16)  .312 .375 (3/8)  .38 • .125 (1/8)  .12 .1875 (3/16)  .188

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