Taps and tapping operation
Hand taps are used in the engine room to repair damaged internal threads and to make new ones after drilling and reaming operations. Taps are identified by the threads they will machine and form, for example M12 x1.5, where M stands for Metric threads (the type of threads used), 12 means 12 millimeter major diameter, and 1.5 stands for the pitch, which in this case is 1.5 mm. Also they are identified as number 1, 2, and 3 or also as Taper, second, and plug or bottoming.
After a hole has been drilled, the number one or taper tap is inserted in the hole, with a tap holder. In taper tap the last five or six threads are ground out to enable the entry of the tap in the hole easily. Care must be taken that the tap is parallel to the hole, this first step is crucial as it will determine whether at the end you get a correctly threaded hole or if you have to do it again after re-drilling (at a larger size). Tapping must be done in stages, a quarter turn clock wise tapping motion, must be followed by similar motion in anti-clock wise direction, to allow for the cut metal bits to come out. Lubrication with water or cutting oil will make the machining easy and protect the taps.
After tapping with the first tap has been done, the hole is cleaned with compressed air, and then the second tap in inserted and tapping is done in the same way. Frequent to and fro movements must be done, any hard obstruction or too much force required must be avoided and the cause investigated. After the tapping has been done a similar sized bolt must be inserted into the hole and the quality of the threads checked.
In holes which are blind, the second tap would not create threads at the end, for this purpose the third tap or the plug or the bottoming one must be used.
Taps and Dies
Dies and die stocks
As taps are used for machining internal threads, threading dies are used for machining external threads and for repairing them. The die operation is used to create external threads on cylindrical items like bolts, studs, and pipes. The die is rotated in the same way is done in the tapping operation. Both cutting and releasing strokes are continued alternatively till the desired length of the rod is threaded. The complete depth of the cut is not obtained in one operation and the jaws should be brought together and the operations repeated. Care should be taken that the die stock is always held at right angles to the axis of the work. Oil or other lubricant should be used for easing the cutting effort.
Screw Pitch Gauge or Thread Gauge
They are used to check the threads and the pitch of threads used in different items. An unknown thread can be identified by the help of this.
Procedure to remove a stud
The studs on any machinery need to be replaced or removed, but it often confuses the junior engineers. The procedure is very simple; take two nuts, first screw the first nut on the stud, then screw the other one till it is touching the first nut. Now take two spanners, hold on the lower nut and tighten the top one very tightly. After they have become tight open with the spanner on the lower nut. The entire stud along with the two nuts will come out. The new stud has to be put in with similar procedure, however during tightening the upper nut must be held with the spanner and tightened.
Procedure to remove a broken stud
Stud removal by a stud extractor
Care of nuts and bolts on board a ship
Nuts and Bolts
The modern sea going ship is of welded construction and houses machinery held together by a number of fasteners, all threaded. Almost every day a marine engineer has to come across threads, in one form or the other. The marine engineer must be aware of the different types of threads used on board, the machining operations to repair a damaged thread or to manufacture a new one. The care of threads in the form of nuts and bolts, their identification, and their inventory management is of utmost importance. In this brief article it has been tried to explain the importance of nuts, bolts, and threads in the everyday life of a marine engineer. It is our endeavor that all sea going junior engineers and senior marine engineers would benefit from this article.
- A course in workshop technology, by B.S. Raghuwanshi. A Dhanpat Rai & Sons Publications.
- Production Technology, by R.K. Jain. A Khanna Publication.
- Materials and processes in manufacturing, by E. Paul DeGarmo, J.T. Black, and Ronald A. Kosher. A Prentice Hall India Publication.
- Stud bolt: https://commons.wikimedia.org/wiki/File:Stud_bolt_1.jpg
- Thread gauge: https://commons.wikimedia.org/wiki/File:Gewindeschablone_Zoll.jpg
- Taps and dies: https://commons.wikimedia.org/wiki/File:Threading_dies_and_screw_taps.jpg
- Nuts and bolts: https://www.flickr.com/photos/west_point/3856380450/
- Iso meteric thread M20: https://commons.wikimedia.org/wiki/File:ISO_metric_thread_M20.JPG
- Castle nut: https://www.flickr.com/photos/[email protected]/128463532
- Wing nut: https://commons.wikimedia.org/wiki/File:Wing_Nut_Cast_Iron.jpg
- Iso metric thread:https://commons.wikimedia.org/wiki/File:Metrisches_kegeliges_Au%C3%9Fengewinde.jpg
- foundation bolt:https://commons.wikimedia.org/wiki/File:Screw_(bolt)_21A-J.PNG
- j bolt u clamp eye bolt:https://commons.wikimedia.org/wiki/File:Screw_(bolt)_21C-J.PNG
- screw:https://www.flickr.com/photos/[email protected]/427383721/
- thread cutting on lathe:https://www.flickr.com/photos/npj/2382008716/
- stud removal:https://moodle.student.cnwl.ac.uk/moodledata_shared/CDX%20eTextbook/dswmedia/images/useScrewextract.jpg