Threaded Fasteners
Introduction
• Design of machine elements needs geometry and joints; single integral parts will not do • Parts are joined by fasteners and they are conveniently classified as permanent, semi-permanent and nonpermanent joints • Permanent :Welded joints, adhesive bonding Semi-permanent : Riveted joints Non-permanent fasteners: Threaded/ non threaded joints
Non threaded joints- keys, pins etc. Threaded joints- screws, bolts and nuts, studs etc.
BITS Pilani, Pilani Campus
Thread Standards and Definitions
BITS Pilani, Pilani Campus
Lead and multi-threaded screws
• Lead is the distance moved by nut parallel to the screw axis when the nut is given one turn. l = p * multiplicity of threading • Single threaded, l=p • Double threaded, l=2p • Triple-threaded, l=3p
Single & Double thread screws
BITS Pilani, Pilani Campus
The Metric Thread nominal major diameter of 12 mm
M12×1.75 mm × metric designation pitch of 1.75 mm
d = major diameter dr = minor diameter = d - 1.226 869p dp = pitch diameter = d - 0.649 519p p = pitch
basic ISO 68 profile with 60◦ symmetric threads
H =
3 p 2
BITS Pilani, Pilani Campus
Square & Acme threads
Square thread
Acme thread
BITS Pilani, Pilani Campus
Power screw or Screw jack mechanism
A device used in machinery to change angular motion into linear motion, and, usually, to transmit power Find use in machines such as universal tensile testing machines, lead screws of lathes and other machine tools, automotive jacks, vises, linear actuators, adjustable floor posts and micrometers etc
BITS Pilani, Pilani Campus
The Mechanics of Power Screws square-threaded power screw single thread Mean diameter ‘dm’ pitch ‘p’ lead angle ‘λ’ helix angle ‘ψ’ loaded by the axial compressive force ‘F’
Helix angle: Angle that thread makes with plane perpendicular to thread axis Lead angle : Angle between the helix and a plane of rotation
BITS Pilani, Pilani Campus
FBD of one thread, (a) raising and
• Design of machine elements needs geometry and joints; single integral parts will not do • Parts are joined by fasteners and they are conveniently classified as permanent, semi-permanent and nonpermanent joints • Permanent :Welded joints, adhesive bonding Semi-permanent : Riveted joints Non-permanent fasteners: Threaded/ non threaded joints
Non threaded joints- keys, pins etc. Threaded joints- screws, bolts and nuts, studs etc.
BITS Pilani, Pilani Campus
Thread Standards and Definitions
BITS Pilani, Pilani Campus
Lead and multi-threaded screws
• Lead is the distance moved by nut parallel to the screw axis when the nut is given one turn. l = p * multiplicity of threading • Single threaded, l=p • Double threaded, l=2p • Triple-threaded, l=3p
Single & Double thread screws
BITS Pilani, Pilani Campus
The Metric Thread nominal major diameter of 12 mm
M12×1.75 mm × metric designation pitch of 1.75 mm
d = major diameter dr = minor diameter = d - 1.226 869p dp = pitch diameter = d - 0.649 519p p = pitch
basic ISO 68 profile with 60◦ symmetric threads
H =
3 p 2
BITS Pilani, Pilani Campus
Square & Acme threads
Square thread
Acme thread
BITS Pilani, Pilani Campus
Power screw or Screw jack mechanism
A device used in machinery to change angular motion into linear motion, and, usually, to transmit power Find use in machines such as universal tensile testing machines, lead screws of lathes and other machine tools, automotive jacks, vises, linear actuators, adjustable floor posts and micrometers etc
BITS Pilani, Pilani Campus
The Mechanics of Power Screws square-threaded power screw single thread Mean diameter ‘dm’ pitch ‘p’ lead angle ‘λ’ helix angle ‘ψ’ loaded by the axial compressive force ‘F’
Helix angle: Angle that thread makes with plane perpendicular to thread axis Lead angle : Angle between the helix and a plane of rotation
BITS Pilani, Pilani Campus
FBD of one thread, (a) raising and