Thread-Cutting Tools and Procedures

1. Thread-Cutting Tools and Procedures Session 9

2. Hand Taps • Cutting tools used to cut internal threads • Made from high quality tool steel, hardened and ground • Two, three, or four flutes cut lengthwise across threads to form cutting edges • Provides room for chips • Admit cutting fluid to lubricate tap • End of shank square so tap wrench can be used to turn tap into hole Shop Tools and Techniques

3. Hand Taps • Inch tap markings • Major diameter • Number of threads per inch • Type of thread ½ in.—13 UNC ½ in. = major diameter of tap 13 = number of threads per inch UNC = Unified National Coarse (type of thread) Shop Tools and Techniques

4. Hand Tap Sets • Taper • Tapered from end six threads • Used to start tapping • Used for tapping through holes and blind hole • Plug • Tapered for three threads • For Tapping through holes • Bottoming tap • Not tapered but chamfered at end • Used for threading to bottom of blind hole Shop Tools and Techniques

5. Identifying Taps Use of annular ring(s) cut around top of shank One – taper tap Two – plug tap Three – bottoming tap Shop Tools and Techniques

6. Tap Drill Size • Hole must be drilled to correct size • Leaves proper amount of material for tap to cut thread (75%) A = body size B = tap drill size C = minor diameter Shop Tools and Techniques

7. Tap Drill Size TDS = tap drill size D = major diameter of tap N = number of threads per inch Find tap drill size for a 7/8 – 9 NC tap Shop Tools and Techniques

8. Metric Taps • Several thread forms and standards in metric thread system • International Standards Organization (ISO) has adopted standard metric thread • Have only 25 thread sizes (1.6 to 100 mm) • Available in sets of three: taper, plug and bottoming taps • Identified by letter M followed by nominal diameter times pitch Shop Tools and Techniques

9. Tap Drill Sizes for Metric Taps Tap drill size for metric taps calculated in same as for Inch threads TDS = major diameter (mm) – pitch (mm) Find the tap drill size for a 22 x 2.5 mm thd TDS = 22 – 2.5 = 19.5 mm Shop Tools and Techniques

10. Tapping a Hole • Operation of cutting internal thread using tap and tap wrench • Taps hard and brittle • Easily broken • Extreme care used to prevent breakage • Broken tap in hole difficult to remove and occasionally results in scrapping work Shop Tools and Techniques

11. Hand Tapping • Select correct taps and tap wrench • Apply suitable cutting fluid to the tap • No fluid required for brass or cast iron • Place tap in hole as vertically as possible • Press downward on wrench, applying equal pressure on both handles • Turn clockwise (for right-hand thread) for two turns Shop Tools and Techniques

12. Hand Tapping • Remove tap wrench and check tap for squareness • Check two positions at 90º to each other • If tap not entered squarely, remove from hole and restart it by applying pressure in direction from which tap leans • When tap properly started, feed it into hole by turning tap wrench Shop Tools and Techniques

13. Hand Tapping • Turn tap clockwise one-quarter turn, and turn it backward about ½ turn to break the chip (must turn with steady motion) • Careful not to tap too deep for a blind hole • When finished, clean hole and check with thread gage or appropriate bolt Shop Tools and Techniques

14. Removing Broken Taps • Several methods may be used to remove broken tap • Tap Extractor • Tool with four fingers that slip into flutes of broken tap; wrench fitted to extractor and turned to extract • Drilling • Drill through broken tap • Tap Disintegrators • Uses electrical current to destroy tap Shop Tools and Techniques

15. Using a Tap Extractor • Select proper size extractor for tap • Slide collar, to which fingers attached, down body so fingers project well below end of body • Slide fingers into flutes of broken tap, making sure they go down into hole as far as possible Shop Tools and Techniques

16. Using a Tap Extractor • Slide body down until it rests on top of broken tap • Slide collar down until it rests on top of work • Apply wrench to square end of body top • Turn wrench gently in counterclockwise direction Do not force extractor – will damage fingers Shop Tools and Techniques

17. Threading Dies • Used to cut external threads on round work • Most common threading dies • Adjustable split die • Adjustable screw plate die • Solid die • Used for chasing or recutting damaged threads • May be driven by suitable wrench • Not adjustable Shop Tools and Techniques

18. Threading Dies • Adjustable split die • Has adjusting screw that permits adjustment over or under standard depth of thread • Fits into die stock Shop Tools and Techniques

19. Threading Dies • Adjustable screw plate die • Two die halves held in collet by threaded plate • Adjusting screws againsteach die half • Greater adjustment than split die Shop Tools and Techniques

20. To Thread With a Hand Die • Chamfer end of workpiece with file or on disk sander • Fasten work securely in vise • Select proper die and die stock • Lubricate tapered end of die with suitable cutting lubricant • Place tapered end of die squarely on workpiece Shop Tools and Techniques

21. To Thread With a Hand Die • Press down on die stock handles and turn clockwise several turns • Check die to see that it has started squarely with work • If not square, remove die and restart • Turn die forward one turn and reverse it approximately one-half turn to break chip Shop Tools and Techniques

22. To Thread With a Hand Die • During threading process, apply cutting fluid frequently • When finished, check with thread ring gage or appropriate nut If thread must be cut to shoulder, remove die and restart it with tapered side of die facing up (complete the thread) Shop Tools and Techniques