Mechanical engineering by kiranraj p sagabala

threads for diploma students

1. ROOT: The root denotes the surface of a thread that connects the adjacent flanks at the bottom of the groove. FLANK: Flanks are the sections of the thread's surface located between the root and crest. They are inclined lines extending from the crest towards the root, forming a solid surface with sloping side surfaces. CREST: The crest is the portion of the thread's surface that connects the adjacent flanks at the top of the ridge. LEAD: Lead is the distance travelled by a nut or bolt in the axial direction during one complete revolution. ANGLE OF THREAD: The angle of the thread is the angle between the flanks, measured in an axial plane. MAJOR DIAMETER: The major diameter refers to the diameter of the imaginary cylinder at the crest or the cylinder on which the threads are cut. MINOR DIAMETER: The minor diameter is the diameter of the imaginary cylinder at the root. PITCH DIAMETER : The pitch diameter is the average of the major and minor diameters.

2. *Machine screws are used for fastening two metallic objects. *They are inserted into already threaded holes that is why machine screws sometimes are also referred to as threaded fasteners. MACHINE SCREWS

3. * Studs that have no head, threads at only one end, and the rest is body * Studs that have threads at both ends, and an unthreaded body in the middle * Studs that have different threads at both ends, and an unthreaded body in the middle * Studs that have different diameters at both ends, and an unthreaded body in the middle * Studs that have a hex or collar in the middle * Studs with a head at one end to be permanently attached to a tapped component via welding, swaging, or bonding STUDS

4. ALLEN BOLTS *These bolts have a hexagonal socket in their head for use with an Allen wrench. FLANGE BOLTS * They have a circular flange, a U bolts shape, under their head that acts as a washer for load distribution. * These can be categorized as U bolts.

5. EYE BOLTS * These bolts have a circular ring instead of a traditional head and are used to fix rope or chain to a surface. GRUB SCREWS * Grub screws are a special type of screw which usually do not have a head. *They are used to prevent movement or rotation between two parts.

6. LOCK NUT / JAM NUT /CHECK NUT It is the most common type of locking device, were two nuts are used to lock. The lower nut is first tightened and the upper nut is tightened upon the lower nut, than the upper nut is held with spanner and the lower nut is slackened back against it. Both the nuts are of same thickness so load is distributed evenly .

7. SPLIT PIN USING ORDINARY NUT

8. SPLIT PIN USING CASTLE NUT Above figure shows the castle nut, in the slotted nuts, the numbers of effective threads are reduced due to the slots which reduces the strength of nut considerably. Therefore, instead of cutting slots within the effective depth, they are cut in the extra cylindrical portion provided at the top of nut, this type of nut is called castle nut. These are used on wheel shaft of automobiles.

9. SPLIT PIN USING SLOTTED NUT Above figure shows the slotted nut, the slotted nut is used instead of the ordinary nut. The slotted nut has slots are cut through the opposite parallel hexagonal faces. When the nut is fully tightened, one set slots on the opposite faces will come in line with the hole in the bolt. The split pin is inserted through the slots in the nut and the hole in the bolt and open ends of split pin.

10. A washer provided with a rectangular projection is called tab washer. This method of locking a nut is suitable when the nut is placed near the vertical edge of the work piece. After the nut is tightened the tab and the projecting portion of the washer itself are bent to bear against the vertical surface of the work piece and one of the lateral faces of the nut. LOCKING BY TAB WASHER

11. LOCKING BY LOCK PLATE In this type of locking nut is tightened and then the lock plate is inserted through the nut. The plate is grooved in such a way that the grooves in the plate receive the hexagonal corners of the nut. The plate is fixed to the bearing surface by a tap bolt screwed into it. Since the nut is held tight within the grooved of the lock plate, the nut is prevented from loosening

12. In this method of locking, a coiled spring washer is placed underneath the nut as shown in fig. When the nut is tightened, the spring force of the spring exerts an axial force on the underside of the nut and holds it by the friction grip, this prevents the loosening of the nut. LOCKING BY SPRING WASHER

13. TYPES OF RIVETED JOINTS DOUBLE RIVETED BUTT JOINT DOUBLE RIVETED LAP JOINT SINGLE RIVETED LAP JOINT