Fasteners

Classification of Fasteners Permanent Welding Brazing Stapling Nailing Gluing riveting Temporary Screws Bolts Keys Pins

Standardization of Threads 1841 Sir Joseph Whitworth (England) 1864 US proposed standards (failed) 1935 US adopted American Standard Thread 1948 US, Canada & Great Britain Unified Screw Thread

Current Thread System ISO (International Organization for Standardization) metric screw threads ANSI (American National Standards Institute)

4 Uses of Threads Fasten parts together Adjustment between parts Measurement Transmit motion or power

Screw Thread Forms Unified National Thread Form (UN) ISO Metric Thread Form Square Thread Form Acme Thread Form Worm Thread Form Knuckle Thread Form Buttress Thread Form

Unified National Thread Form (UN)

ISO Metric Thread Form

Square Thread Form

Acme Thread Form

Worm Thread Form

Knuckle Thread Form

Buttress Thread Form

Thread Terms

Tap vs Die Process The Simplest Method to produce inside and outside threads. Tap – Cuts internal threads; in making an internal threaded hole, a tap-drilled hole must be drilled first, hole is approx. the same diameter as the minor diameter of the threads. Die – Cuts external threads.

Methods for Measuring TPI Place a standard scale on the crest of the threads, parallel to the axis, and count the number of full threads within on inch of the scale. or Screw Thread Gage the various fingers or leaves of the gage are placed over the threads until one is found that fits exactly into all the threads.

Pitch The pitch of any thread regardless of its thread form or profile, is the distance from point on a thread to the corresponding point on the adjacent thread as measured parallel to its axis. Pitch is found by dividing the TPI into one inch

Single and Multiple Threads Single thread is composed of one continues ridge. The lead of a single thread is equal to the pitch. Lead is the distance a screw thread advances axially in one full turn. Multiple threads are made up of two or more continuous ridges following side by side. The lead of a double thread is equal to twice the pitch. The lead of a triple thread is equal to three times the pitch.

Right and Left hand Threads It follows the right hand rule Right – Clockwise, Left- Anti-Clockwise Right hand threads winding tends to lean towards the left.

Thread Representation Schematic Simplified

Thread Relief Where mating parts must be held tightly against the shoulder, the last one or two threads must be removed or relived.

Screw / Bolt / Stud Screw- a fastener that does not use a nut and is screwed directly into a part. Bolt- a threaded fastener that passes directly through parts that hold them together. Stud- a fastener that is a steel rod with threads at both ends.

Methods for drawing Screws, Bolts and Studs Take your time. Put a lot of pride into your work. Try to draw on a scale that you will be able to work with.

Rivets Rivets are permanent mechanical fasteners that consist of a smooth cylinder shaft with a head on one end and an opening on the other end.

Keys and Keyseats Key- a demountable part that provides a positive means of transferring torque between a shaft and a hub. 5 major keys= square, flat, gib head, Pratt & Whitney, and Woodruff. Keyseat- an auxiliary located rectangular groove machined into the shaft and/or hub to receive the key

Grooved Fasteners Used to solve metal-to-metal pinning needs with shear application Great power. Resistant to shock, vibration, and fatigue Have 3 parallel grooves equally spaced, impressed longitudinally on there exterior surface.

Spring Pins

Fastening Systems

Retaining Rings