1. MACH 112: Cutting Tools & Measurement
Taps & Tapping
MACH 112: Cutting Tools & Measurement

2. OBJECTIVES
After completing this unit, you should be able to…
Identify common taps.
Select taps for specific applications.

3. Identifying Common Tap Features
IDENTIFICATION AND USES OF TAPS
Identifying Common Tap Features
Taps cut internal threads in holes, called tapping.
The active cutting part of the tap is the chamfer, produced by grinding away the tooth form at an angle, with relief back of the cutting edge.
Cutting action is distributed progressively.
The fluted portion of the tap provides space for chips to accumulate & passage of cutting fluids.
Two-, three-, and four-flute taps are common.

4. Identifying Common Tap Features
IDENTIFICATION AND USES OF TAPS a
Identifying Common Tap Features
Fig. B-114 Chamfer designations for cutting taps. Top to bottom: starting tap, plug tap & bottoming tap.
Fig. B-113 General tap terms (Besly Cutting Tools, Inc.).

5. Identifying Common Tap Features
IDENTIFICATION AND USES OF TAPS
Identifying Common Tap Features
Taps are made from either high-carbon or high-speed steel & hardness of about Rockwell C63.
High-speed steel taps are far more common in manufacturing plants than carbon steel taps.
Typically are ground after heat treatment to ensure accurate thread geometry.

6. Identifying Common Tap Features
IDENTIFICATION AND USES OF TAPS
Identifying Common Tap Features
A set consists of three taps: taper, plug & bottoming, identical except for number of chamfered threads.
The taper tap
useful in starting a tapped hole.
1st 6 threads are tapered
The plug tap.
Most commonly used tap
First 3 threads are tapered
The Bottoming tap
threads extend almost to the bottom of a blind hole.
Should be used after plug tap.

7. Identifying Common Tap Features
IDENTIFICATION AND USES OF TAPS
Identifying Common Tap Features
A tap used for tough metal such as stainless steel is the interrupted thread tap (Fig. B-115).
It has alternate teeth removed to reduce tapping friction.
Fig. B-115 Interrupted thread tap.

8. Identifying Common Tap Features
IDENTIFICATION AND USES OF TAPS
Identifying Common Tap Features
Identifying markings of a tap
5/8” is the nominal size, 11 the number of threads per inch.
NC refers to standardized National Coarse thread series.
G is the symbol used for ground taps.
H3 identifies the tolerance range of the tap.
Left-hand taps are identified by an LH or left-hand marking.

9. Other Kinds and Uses of Taps
IDENTIFICATION AND USES OF TAPS
Other Kinds and Uses of Taps
Spiral pointed taps (Fig. B-117), called gun taps, are useful for machine tapping of through holes or blind holes with chip room below the threads.
When the spiral point is turned, the chips are forced ahead of the tap (Fig. B-118).
Fig. B-117 Set of spiral pointed (or gun) taps.
Fig. B-118 Cutting action of spiral pointed taps.

10. Other Kinds and Uses of Taps
IDENTIFICATION AND USES OF TAPS a
Other Kinds and Uses of Taps
If a spiral pointed tap is used to tap a blind hole, sufficient hole depth is necessary to accommodate the chips that are pushed ahead of the tap.
Spiral pointed taps can operate at higher speeds & require less torque to drive than ordinary hand taps.
Fig. B-119 shows the design of the cutting edges.
The cutting edges at the point of the tap are ground at an angle to the axis.
Fig. B-119 Detail of spiral pointed tap.

11. Other Kinds and Uses of Taps
IDENTIFICATION AND USES OF TAPS
Other Kinds and Uses of Taps
Fluteless spiral pointed taps are recommended for production tapping of through holes in sections no thicker than the tap diameter.
This type of tap is strong and rigid, which reduces tap breakage caused by misalignment.
Fluteless spiral point taps give excellent results when tapping soft materials or sheet metal.
Fig. B-120 Fluteless spiral pointed tap for thin materials.

12. Other Kinds and Uses of Taps
IDENTIFICATION AND USES OF TAPS
Other Kinds and Uses of Taps
Spiral fluted taps are made with helical flutes instead of straight flutes which draw chips out of the hole.
Spiral fluted taps are recommended for tapping deep blind holes in ductile materials such as aluminum, magnesium, brass, copper, and die-cast metals.
Fig. B-121 Spiral fluted taps––regular spiral.

13. Other Kinds and Uses of Taps
IDENTIFICATION AND USES OF TAPS
Other Kinds and Uses of Taps
Thread-forming taps are fluteless and do not cut threads in the same manner as conventional taps.
They are forming tools, and their action can be compared with external thread rolling.
Thread-forming taps are held and driven just like conventional taps, but because they do not cut the threads, no chips are produced.
Fig. B-123 Fluteless thread-forming tap.

14. Other Kinds and Uses of Taps
IDENTIFICATION AND USES OF TAPS
Other Kinds and Uses of Taps
Fig. B-124 shows how the thread-forming tap displaces metal.
The crests of the thread at the minor diameter may not be flat but will be slightly concave because of the flow of the displaced metal.
Fig. B-124 The thread-forming action of a fluteless thread-forming tap.
Threads produced in this manner have improved surface finish and increased strength because of the cold working of the metal.

15. Other Kinds and Uses of Taps
IDENTIFICATION AND USES OF TAPS
Other Kinds and Uses of Taps
Fig. B-125 Taper pipe tap
A tapered pipe tap is used to tap holes with a taper of 3/4” per foot for pipes with a matching thread & produce a leakproof fit.
Straight pipe taps are used for tapping holes or couplings to fit taper-threaded pipe and to secure a tight joint when a sealer is used.
Fig. B-126 Straight pipe tap.

16. Other Kinds and Uses of Taps
IDENTIFICATION AND USES OF TAPS
Other Kinds and Uses of Taps
A pulley tap is used to tap set screw and oil-cup holes in the hubs of pulleys.
The long shank also permits tapping in places that might be inaccessible for regular hand taps.
Fig. B-127 Pulley tap.
Nut taps differ from pulley taps in that their shank diameters are smaller than the root diameter of the thread, which makes tapping deep holes possible.
Fig. B-128 Nut tap.

17. Other Kinds and Uses of Taps
IDENTIFICATION AND USES OF TAPS
Other Kinds and Uses of Taps
Acme threads provide accurate movement.
In lead screws on machine tools and for applying pressure in various mechanisms.
Fig. B-129 Set of Acme thread taps. The upper tap is used for roughing, the lower tap for finishing.
On some Acme taps the roughing and finishing operation is performed with one tap
The length of this tap usually requires a through hole.
Fig. B-130 Tandem Acme tap designed to rough and finish cut the thread in one pass.

18. REVIEW What 3 different taps are found in a set?
How many threads are tapered on a plug tap?
What is an interrupted thread tap used for?
Identify the following markings: ¾-10 UNC
What does the marking H3 represent?
What is a gun tap?
Gun taps are best at tapping what type of hole?
What materials are fluteless spiral point taps used on.
What limitation must be observed when using a Fluteless- spriral- point taps?
What is the advantage of spiral fluted taps?
State two advantages to using thread forming taps.
What’s the difference between pulley taps and nut taps.
What type of tap both roughs and finishes threads?