page 64

7.3.2 Boring

• Boring is used for high quality finished.

cutting point

boring bar

Workpiece

• In boring the tool can be rotated, or the work can be rotated.

7.3.3 Taps

•Taps can use for both internal and external threads.

•A typical set of hand taps consists of

-#1 Taper

-#2 Plug

-#3 Bottoming

•There are flutes in the taps to help remove chips, to provide cutting edges, and channels for lubrication.

•There are a number of sets of threads available,

-UNC (Unified National Course)

-UNF (Unified National Fine)

-ACME

-Metric

•To create one of these holes, we must first drill a hole that is slightly smaller. For example,

page 65

5/8 - 11 - UNC

outside diameter = 5/8 = 0.625” 11 threads per inch (T.P.I.)

Unified National Coarse is the tooth profile

The tap drill size is Outside Diameter - 1/T.P.I. for UNC, UNF, Metric threads.

Therefore, the Tap Drill Size (TDS) is,

T.D.S. = 0.625” - 1/11” = 17/32”

•Some setups associated with taps are,

-alignment of the tap in a drill press

-use of taping attachments

•NF/NC Thread Tap Drill Sizes [Krar],

National Coarse (NC)					National Fine (NF)
Tap Size		TPI	Tap Drill Size		Tap Size		TPI	Tap Drill Size
#5		40	#38	#5			44	#37
#6		32	#36	#6			40	#33
#8		32	#29	#8			36	#29
#10		24	#25	#10			32	#21
#12		24	#16	#12			28	#14
1/4		20	#7	1/4			28	#3
5/16		18	F	5/16			24	1
3/8		16	5/16	3/8			24	Q
7/16		14	U	7/16			20	25/64
1/2		13	27/64	1/2			20	29/64
9/16		12	31/64	9/16			18	33/64
5/8		11	17/32	5/8			18	37/64
3/4		10	21/32	3/4			16	11/16
7/8		9	49/64	7/8			14	13/16
1		8	7/8	1			14	15/16
1-1/8		7	63/64	1-1/8			12	1-3/64
1-1/4		7	1-7/64	1-1/4			12	1-11/64
1-3/8		6	1-7/32	1-3/8			12	1-19/64
1-1/2		6	1-11/32	1-1/2			12	1-27/64
1-3/4		5	1-9/16
2		4-1/2	1-25/32