कोशिश .....An Effort by Ankush Chauhan
Before Understanding threading operations we need to know something about thread , it's type, nomenclature etc.
Thread is a helical groove on a cylindrical surface outside or inside. It is used to make threaded fasteners.
Nomenclature of thread is as following
1. Pitch - it is the distance between two corresponding points on the consecutive thread.
2.Crest- it is the top surface joining the two sides of a thread.
3. Root - The bottom surface joining the two sides of a thread.
4. Depth of Thread - it is the distance measured perpendicular to the axis between Crest and root.
5. Thread angle- it is the angle between the flanks measured in an axial plant.
6. Flank- it is the surface between the Crest and the root if the thread.
7.Lead- In single start thread lead is the axial advance nut in one complete turn. And is equal to the pitch and in double start thread lead is twice the pitch.
8. Major diameter- it is also called outside of nominal diameter is the largest diameter of a screw thread.
9. Minor diameter- it is also called root or core diameter. It is smaller diameter external or internal thread.
10. Pitch diameter- it is called effective diameter it is the diameter of an imaginary cylinder, on a cylindrical screw . In a nut and bolt assembly, it is the diameter at which the ridges on the bolt are in complete touch with the ridges of the corresponding nut.
11. Single start thread- when all the thread are built ona single helix it is called single start thread or single thread.
12.Double start thread- whan a thread has two starting point and two equally spaced thread are wrapped with two parallel helices.
13. Multi start thread- when quick advance is required multi thread are used in this two or more then two thread are cut side by side.pitch remain fixed for a particular types of thread.
Types of thread
1. B. S. W ( British Standard Thread) -The BSW basic thread form is a symmetrical V thread in which the angle between the flank , measured in an axial plane, is 55° thread is rounded equally at roots and Crest.
2. B. A. ( British Association) Standard Thread- The basic thread form ia a symmetrical V thread with angle between flank are 47.5°
3. Unified screw thread- This thread system has angle of flank at 60* and on bolt is rounded at Crest and root but in nut rounded off at the root only.
5. American Standard Thread- it is also called seller's thread it used for general purpose. It has flat top and bottom with angle of 60° at flank.
6. Square thread- it is used for power transmission like in screw jacks . It is flat at root and top with flat flank.
7.matric thread- it is basic V thread and defined by nominal size and pitch both expressed in matric ( milimete)
8.ACME Thread- it is the modified form of square thread . It stronger than square thread . It has a 29° thread angle and is flat at top and bottom.
9.Buttress thread- it is used when power is to transmitted in one direction.the force is transmitted almost parallel to the axis and the thread is about the same strength and the standard V thread . Bench vice are usually fitted with spindle having buttress thread.
10. Knuckle thread- it is the modified square thread . It has round top and bottom and can be made on a machine. It is not easily damaged When subjected to rough usage.
How to make thread
There are many process to make thread thread can be made on machine or by hand tools.
1. External thread cutting on lathe- lathe is a conventional machine on which we can cut thread also .watch video
2. External thread cutting by die- die is a hand tool to cut the thread . it is a tool which is used with a handle to cut the thread.watch video
3. External thread cutting by rolling-rolling is a thread forming process this is the process in which thread is rolled on the job by a forming tool . watch video
4. Internal thread cutting by tapping- tap is a hand tool to make internal thread it can be used by a hand with a tap handle on can use by a machine also. Before cutting thread by tap we need to make desired hole by drilling.