Upload
lydia-bryan
View
227
Download
0
Tags:
Embed Size (px)
Citation preview
ADVANCED MECHANICAL DRAFTING
LECTURE #3
Common Hole Types
DRILLED
REAMED
BORED
COUNTERBORED
COUNTERSUNK
SPOTFACED
DRILLING
• Specifying drilled holes on drawings
Ø.250 (1/4) THRU
or
Ø.250 (1/4) .50
• Drill names
• Drill size chart
CLEARANCE HOLES
• Used for holes that accommodate fasteners (usually screws)
• Must be larger diameter than the screw for a clearance fit
• Tapping section of MHB contains necessary data
• Must be THRU holes
CLEARANCE HOLES
EXAMPLE:
Specify clearance hole for 3/8” screw on the drawing.
Ø.397 (X) THRU
USE “FREE FIT” CLEARANCE HOLES UNLESS OTHERWISE
SPECIFIED
GSSP FASTENERS
¼” SOCKET HEAD CAP SCREW & ¼” MEDIUM LOCK WASHER
SOCKET HEAD CAP
SCREW
LOCK WASHER
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
FIRST NOTE LINE
SECONDNOTE LINE
ROUNDING DECIMAL DIMENSIONS
• Rounding Rules– Round digits > 5 UP – Round digits < 5 DOWN – Round 5 UP if previous digit is ODD– Round 5 DOWN 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
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