Mechanical Engineering Technology

Topic: Internal Screw Thread Cutting.

Objectives : Students should be able to:• Define internal screw thread.• State explain the uses of taps • Calculate tap size drill.• State precautions associated with screw thread

cutting.

Cutting Internal Threads

Internal threads are made by using a tap. Taps are made of Carbon Steel or High Speed Steel (HSS) and are carefully hardened and tempered for long life. Taps are quite brittle and are easily damaged if not handled properly.

Internal Threads

Taps are usually made in sets of three

• Taper Tap• Second or Intermediate Tap• Plug or Bottoming tap

TAPER OR FIRST TAP

SECOND OR INTERMEDIATE

PLUG OR BOTTOMING TAP

Tools used for holding Taps Adjustable Tap Wrench

Chuck Pattern Tap Wrench

How to use wrench and tap together.

INTERNAL SCREW THREADS CUTTING

STEPS

1. A hole must be drilled. This hole is called Tapping Size Hole.Formula= D-P

where D= Major Diameter P= Pitch

Example- M10 * 1.5Tapping Size= 10-1.5

=8.5mm 2. Clamp work securely in a bench vice, level and square.3. Make clockwise turns to start the threads and anti-clockwise turns

to break the chip4. Oil must be used to lubricate the threads.

Care in Tapping Considerable care must be exercised when

tapping. Use the tap before the die because the taps are non-adjustable for size, the dies are Start the tap square. Use a cutting solution where necessary.

Care in Tapping Cont’d Ensure that a blind hole is drilled

deeper than the depth of thread required to allow clearance for chipping.

Do not force a tap to cut. Remove the chips as necessary.

Internal THREAD

HEX NUT25

M10x1.5

True or False Taps are made in sets of 3. Taps are made of high tensile steel. Taps are usually very brittle.

Quiz Time

Quiz TimeIdentify the taps shown below

Quiz TimeIdentify the tap shown below

Quiz TimeIdentify the tap shown below

Quiz TimeIdentify the tool shown below