screw threads - bema•sti special thread for helical coil wire screw thread inserts •stub acme...

Unit 047: Advanced Turning

Screw threads

Starter activity

• When was the screw thread invented?

• Who was the inventor of the most famous screw thread form?

• When was the first unified British thread invented and by who?

When was the screw thread invented?

• Around 400BC

Who was the inventor of the most famous screw thread form?

• Archimedes

When was the first unified British thread invented and by how?

• 1860

Starter activity

• When was the metric thread form suggested as the preferred choice to replace the old British system?

• How many different types of thread forms are there?

Starter activity 2

• When was the metric thread form suggested as the preferred choice to replace the old British system?

• 1965

• How many different types of thread forms are there?

• 50 plus

Starter activity 2

Thread formats

• ACME-C Acme Thread-Centralizing

• ACME-G Acme Thread-General PurposeA

• MO American Standard Microscope Objective Thread

• ANPT Aeronautical National Form Taper Pipe Thread (Ground thread tap marked NPT)

• BA British Association Standard Thread

• BSF British Standard Fine Thread Series

Thread formats

• N BUTT American Buttress Screw Thread

• NC American National Coarse Thread Series

• NEF American National Extra Fine Thread Series

• NF American National Fine Thread Series

• NGO National Gas Outlet Thread

• NGT National Gas Taper Thread (see "SGT")

• NH American National Hose Coupling and Fire Hose Coupling Threads

• NPS For tap marking only (See NPSC, NPSM)

• NPSC American National Standard Straight Pipe Thread in Pipe Couplings (Tap marked NPS)

• NPSF Dryseal American National Standard Fuel Internal Straight Pipe Thread

• BSPP British Standard Pipe (Parallel) Thread

• NPSH American National Standard Straight Pipe Thread for Hose Couplings

Thread formats

Thread formats

• NPSI Dryseal American National Standard Intermediate Internal Straight Pipe Thread

• NPSL American National Standard Straight Pipe Thread for Loose Fitting Mechanical Joints with Locknuts

• NPSM American National Standard Straight Pipe Threads for Free-Fitting Mechanical Joints for Fixtures (Tap marked NPS)

• NPT American National Standard Taper Pipe Thread (See ANPT, NPTR)

• NPTF Dryseal American National Standard Taper Pipe Thread

• *UN Unified Constant Pitch Thread Series

• *UNC Unified Coarse Thread Series

• *UNEF Unified Extra Fine Thread Series

• *UNF Unified Fine Thread Series

Thread formats

Thread formats

• NPTR American National Standard Taper Pipe Thread for Railing Joints (Tap marked NPT)

• NS American National Thread-Special

• PTF Dryseal SAE Short Taper Pipe ThreadS

• GT Special Gas Taper Thread

• SPL-PTF Dryseal Special Taper Pipe Thread

• STI Special Thread for Helical Coil Wire Screw Thread Inserts

• Stub Acme Stub Acme Thread

Thread formats

• UNJ Unified Thread Series with a 0.15011P to 0.18042P Controlled Root Radius on External Thread only.

• UNJC Unified Coarse Thread Series with a 0.15011P to 0.18042P Controlled Root Radius on External Thread only.

• UNJF Unified Fine Thread Series with a 0.15011P to 0.18042P Controlled Root Radius on External Thread only.

Thread formats

• UNRC Unified Coarse Thread Series with a 0.108P to 0.144P Controlled Root Radius; Ext. thread only.

• UNRF Unified Fine Thread Series with a 0.108P to 0.144P Controlled Root Radius; External thread only.

• *UNS Unified Thread-Special

• V A 60° "V" thread with Truncated Crest and Root. The theoretical "V" Form is usually flatted to the user's specifications.

• BSPT British Standard Taper Pipe Thread

• BSW British Standard Whitworth Coarse Thread Series

• M Metric ScrewThread Series

• N American National 8, 12 and 16 Thread Series (8N, 12N, 16N)

• WHIT British Standard Whitworth Special Thread

Thread formats

• UNM Unified Miniature Thread Series

• UNR Unified Constant Pitch Thread Series with a 0.108P to 0.144P Controlled Root Radius; Ext. thread only.

Thread formats

Thread nomenclature

Thread nomenclature

Thread nomenclature

Thread nomenclature

Multi start threads

Thread forms

• Square.

• Size unlimited.

• No accepted relationship between pitch and diameter.

• Used for transmission of power, little friction.

Thread forms

• Acme.

• Size: unlimited.

• Replaces the square thread for many purposes, e.g. lathe, lead screws, power transmission and motion.

Thread forms

• Buttress.

• Size: unlimited.

• Used for quick release mechanism, e.g. vice.

Thread forms

• B.A (British Association) No. 0 to No. 10.

• Used for small instrument work. A full range goes down to No. 30.

• Teeth expressed in pitch not TPI

Thread forms

• B.S.W (British Standard Whitworth) 1/8’’ to 3’’. Coarse pitch, used for general engineering and for threads in soft materials.

• B.S.F (British Standard Fine) 3/16’’ to 2’’. Fine pitch, used for parts subject to vibration; lock nuts

Thread forms

• ISO (International Organization for Standardization)

• Metric system is now adopted as the standard screw thread in this country.

• The thread form shown is that for a nut.

P= Pitch

H= Height

Making thread forms

Thread Milling

Making thread forms

Thread Milling - ext

Making thread forms

Thread Rolling

Internal threads

Internal threads are produced with taps. This is a “First” tap which is used to start producing the thread form in a hole

Internal threads

This is a “Second” or “Intermediate” tap which is used after the “First” tap has been used.

Internal threads

This is a “Plug” or “Bottoming” tap which is used to finish the threaded hole.

External threads

Split dies are used to produce external threads on a diameter.

External threads

A die nut is normally used to repair a thread that has become damaged.

Die StockTap Wrench

2

1

3

Die and tap holders

Assessment for learning

You need be able to know the nomenclature of threads and how they can be produced.

Completing HF WS003 and WS007 will help reinforce your knowledge on the topic?