1. Chapter 42: Thread and Gear Manufacturing
DeGarmo’s Materials and Processes in Manufacturing

2. 42.1 Introduction
FIGURE 42-1 Standard screwthread
nomenclature.

3. Fig. 29-A Symbols for threads. A, Unified system. B, ISO system
(Source: P.F. Ostwald and J. Munoz, Manufacturing Processes and Systems, John Wiley & Sons, 1997)

4. UN Thread Example 1 (nominal diameter less than 1/4 in)
UNC
A number (1 through 12)
is used for a thread having
its nominal diameter less
than 1/4 in.
UNC: coarse thread
Threads/in
Nominal size
(#4 thread: major diameter = in)
UNF
UNF: fine thread
Threads/in
Nominal size
(#4 thread: major diameter = in)

5. UN Thread Example 2 (nominal diameter more than 1/4 in)
1/ UNC
UNC: coarse thread
Threads/in
Nominal size
(major diameter = 0.5 in)
1/ UNF
UNF: fine thread
Threads/in
Nominal size
(major diameter = 0.5 in)

6. UN Thread Example 3 (nominal diameter = 4 in, Compare this with Example 1)
4 - 4 UNC
UNC: coarse thread
Threads/in
Nominal size
(major diameter = 4 in)

7. ISO Thread Examples Pitch, mm
Nominal size, mm (major diameter = 2.5 mm)
M: M stands for ‘metric thread’
Some nominal size thread has several options for pitch size.
For example, for M16 threads
M16  2
M16  1.5

8. 42.2 Thread Making

9. FIGURE 42-5 (below) Two ways to feed the threading tool into the workpiece.
FIGURE 42-4 (above) Cutting a screw
thread on a lathe, showing the
method of supporting the work
and the relationship of the tool
to the work with the compound
swiveled. Inset shows face of
threading dial.

10. FIGURE 42-6 Canned
subroutines called G codes are
used on CNC lathes to produce
threads. See Chapter 26 for CNC
discussion.

11. FIGURE 42-7 (a) Solid
threading die; (b) solid adjustable
threading die; (c) threading-die stock for round die (die removed). (Courtesy of
TRW-Greenfield Tap & Die.)

12. FIGURE 42-8 Self-opening die
heads, with (a) radial cutter,
(b) tangential cutters, (c) circular
cutters, and (d) terminology of
circular chasers and their relation
to the work. (Courtesy of Geometric
Tool Company, Warner & Sawsey
Company, National Acme Company,
and TRW-Greenfield Tap & Die,
respectively.)

13. 42.3 Internal Thread FIGURE 42-9 Terminology for a
plug tap with photographs of
taper (t), plug (p), and bottoming
(b) taps, which are used serially in
threading holes. (Courtesy of TRW Greenfield
Tap & Die.)

14. FIGURE 42-10 (Left to right)
Spiral-fluted tap; spiral-point tap;
spiral-point tap cutting chips;
fluteless bottoming tap and
fluteless plug tap for cold forming
internal threads; cross
section of fluteless forming tap.
(Courtesy of TRW-Greenfield Tap
& Die.)

15. 42.4 Thread Milling FIGURE 42-12 Thread milling
on a three-axis NC machine can
produce a complete thread in a
single feed revolution. (Fred
Mason, American Machinist,
November, 1988.)

16. FIGURE 42-12 Thread milling
on a three-axis NC machine can
produce a complete thread in a
single feed revolution. (Fred
Mason, American Machinist,
November, 1988.)

17. FIGURE The process of high-speed thrilling (drilling plus threading) a hole includes (1) approach, (2) drill plus chamfer, (3) retract one thread
pitch, (4) radially ramp to the major thread diameter, (5) thread-mill with helical interpolation, (6) return the tool to the centerline of the hole, and (7) retract from the finished hole. At 20,000 rpm, a hole can be thrilled in aluminum in less than two seconds. (Fred Mason, American Machinist, November,
1988.)

18. 42.6 Thread Rolling
FIGURE Roll forming threads using flat die thread rolling process shown in (a) and (b). The threads forming action is
shown in (c) and the product in (d). Three variations of cylindrical rolling are shown in (e), (f), and (g).

19. FIGURE Roll forming threads using flat die thread rolling process shown in (a) and (b). The threads forming action is
shown in (c) and the product in (d). Three variations of cylindrical rolling are shown in (e), (f), and (g).