Threading on a lathe involves cutting helical grooves on a workpiece to form threads. This is achieved by using a cutting tool that moves linearly along the workpiece as it rotates.
- 1. THREADING Group III – BSME 1B Alanis Cruza – Angelica Ann Josol – Billchrist Ian Lanquino – Darwin Minoza – Janraynar Pahang Jay Bonghanoy – John Albert Hansol – John Glenie Vee Bonhayag – John Mark Rian Olayan
- 2. In metalworking, a thread is a helical ridge or groove cut onto a cylindrical surface, creating a screw-like shape. This allows for a secure and easily removable connection between two parts What is Thread?
- 4. THREAD CLASS (FIT) Defines the tolerance and allowance for thread engagement. Determines how loose or tight the fit will be. THREAD SERIES A standard grouping based on thread pitch and diameter . (UNC, UNF, ISO Metric). Defines thread compatibility and usage.
- 5. THREAD FORM The shape of the thread in cross-section. Determines strength and intended application. CHAMFER A beveled edge at the beginning of the thread. Aids in thread engagement and prevents cross-threading.
- 6. ▸ Distance the screw moves forward in one complete revolution. LEAD For single-start threads: lead = pitch For multi-start: lead = pitch × number of starts.
- 7. For single-start threads: lead = pitch For multistart: lead = pitch × number of starts.
- 8. RIGHT HAND THREAD ▸ Tightens when turned clockwise. ▸ Most common thread direction.
- 9. LEFT HAND THREAD ▸ Tightens counterclockwise. ▸ Used where right-hand threads might loosen (e.g., on rotating parts).
- 10. THREAD CUTTING TOOLS ▸ Special tool with a pointed or shaped tip matching the thread profile. ▸ Used on a lathe for cutting external or internal threads.
- 11. THREAD RELIEF ▸ A small groove or recessed area at the end of the thread. ▸ Allows clean thread termination and tool withdrawal.
- 12. PARTS OF SCREW THREADS AND FUCTIONS
- 13. ALLOWANCE Allowance is the difference between the maximum size of the thread and the basic size. It is usually a gap that functions as clearance but can be interference (as with NC thread forms).
- 14. CHAMFER Chamfer is a conical surface at the end of a thread. The chamfer allows easy engagement of threaded parts and prevents the formation of a sharp edge on the first thread.
- 15. CREST The top or outermost surface of the thread. It helps form the thread profile.
- 16. FLANK The flank angle is the angle formed between the flank and an axis perpendicular to the axis of the thread. On symmetrical threads the flank angle is equal to half of the thread angle. Helps distribute force between mating threads.
- 17. THREAD DEPTH Vertical distance from crest to root. Controls how "deep" the thread is cut.
- 18. THREAD ANGLE ▸ The included angle between the flanks. ▸ Standard angle is 60° for metric and unified threads.
- 19. MAJOR DIAMETER Diameter measured from crest to crest (external threads).Largest diameter, used for screw sizing.
- 20. MINOR DIAMETER Diameter from root to root. Smallest diameter of the thread.
- 21. PITCH Distance between two adjacent thread crests (measured parallel to the axis). Determines thread tightness and screw travel per turn. The pitch is the distance between corresponding points on adjacent threads. It is the distance from one thread to the next.
- 22. ROOT The root of a thread connects flanks of adjacent threads. It is the bottom of the thread.
- 23. PITCH DIAMETER Imaginary diameter where the thread width equals the space between threads. Crucial for thread fit and engagement.
- 24. TWO KINDS OF THREADS
- 25. INTERNAL THREADS Threads that are cut inside a hole (like those in nuts or tapped holes in parts). They allow an externally threaded component (like a bolt or screw) to be inserted and secured.
- 26. INTERNAL THREADS A tapped hole in a machine part that receives a bolt. FUNCTION: Provide holding force for bolts/screws. Allow the connection of components. Often used in tapped holes or nuts. EXAMPLES: The threaded hole in a nut. Threaded pipe fittings.
- 27. EXTERNAL THREADS Threads that are cut on the outside of a cylindrical or conical component (like screws or bolts).
- 28. INTERNAL THREADS Threaded studs. FUNCTION: Engage with internal threads to form a secure joint. Used to transmit force, motion, or to assemble parts. EXAMPLES: Bolts and screws. Threaded end of a pipe.
- 29. THREE TYPES OF THREAD
- 30. SINGLE THREAD A single thread is a helical ridge wrapped around a cylinder (or cone) with only one continuous thread that advances axially with each turn. (Single-Start Thread)
- 31. SINGLE START THREAD ▸For every one revolution, the screw advances one pitch length. ▸ Simple design, easy to manufacture. APPLICATION: ▸ Most commonly used in fasteners like bolts, nuts, and screws. ▸ Where strength and holding power are more important than speed
- 32. MULTIPLE THREAD Multiple threads (also called multistart threads) have two or more thread "starts" that are evenly spaced around the screw cylinder. These threads run parallel and do not overlap. (Multi-start Thread)
- 33. MULTI-START THREAD ▸ Threads advance faster because there are multiple threads engaging at the same time. ▸ Example: A double-start thread has two threads starting 180° apart; it advances 2 pitch lengths per turn. ▸ Reduces wear and increases efficiency in applications where speed or smoother motion is needed. ▸ Lower mechanical advantage but higher speed of operation. APPLICATIONS: ▸ Lead screws in lathes and CNC machines ▸ Jar lids (twist less to close) ▸ High-speed motion transmission components`
- 34. TAPER THREAD A taper thread has a gradually decreasing (or increasing) diameter along its length, unlike parallel threads that maintain a consistent diameter.
- 35. TAPER THREAD ▸The threads are cut on a conical surface. ▸ When tightened, the threads compress to form a tight, leak-proof seal. ▸ Often used for fluid or gas-tight applications without needing sealing tape or O-rings (though sometimes used as backup). ▸ The taper angle is standardized (e.g., 1 in 16 for BSPT). APPLICATIONS: ▸ Pipe fittings (e.g., NPT – National Pipe Taper, BSPT – British Standard Pipe Taper) ▸ Plumbing, gas lines, hydraulic fittings
- 37. METRIC THREADS M The international ISO standard, widely used in most countries outside the US. Metric threads have a 60° thread angle and are designated by diameter and pitch in millimeters.
- 38. UNIFIED THREADS UNC, UNF, UNEF The primary standard in the US and Canada. Unified threads also use a 60° thread angle and are specified by threads per inch TPI) and diameter in inches. Variants include: UNC Unified National Coarse) UNF Unified National Fine) UNEF Unified National Extra Fine).
- 39. BRITISH STANDARD FINE Similar to BSW but with a finer pitch for each diameter, offering a stronger grip in applications subject to vibration
- 40. BRITISH STANDARD PIPE Used for pipe fittings, with two main types: BSPP Parallel, "G- thread") BSPT Tapered, "R-thread").
- 41. NATIONAL PIPE THREAD The American standard for tapered pipe threads, providing a pressure- tight seal. Used in plumbing and hydraulic systems .
- 42. ACME THREAD A trapezoidal thread form 29° angle) designed for power transmission and high-load applications. Easier to machine than square threads and used in lead screws and vises.
- 43. SQUARE THREAD Offers maximum efficiency for power transmission but is more difficult to manufacture. Used in applications requiring minimal friction, such as jacks and presses.
- 44. BUTTRESS THREAD Asymmetrical trapezoidal profile, designed to handle high axial loads in one direction. Common in heavy-duty equipment and jacks.
- 45. KNUCKLE THREAD Asymmetrical trapezoidal profile, designed to handle high axial loads in one direction. Common in heavy-duty equipment and jacks.
- 46. WORM THREAD Used in worm gears, featuring a profile suitable for sliding contact.
- 47. THREE CLASSIFICATION OF EXTERNAL AND INTERNAL THREAD
- 48. THREAD SERIES (PITCH) The distance between threads (pitch) and the number of threads per inch (TPI). • Coarse (UNC/UNRC) – Fewer threads per inch; stronger and faster to assemble. • Fine (UNF/UNRF) – More threads per inch; better for precision and stronger holding. • Extra Fine (UNEF) – Used for very precise and delicate applications.
- 49. THREAD FORM OR PROFILE Defines the shape of the thread’s cross-section: • Unified Thread (UN) – Common in the US, uses a 60- degree angle. • Metric Thread (M) – Used internationally, also a 60- degree angle. • Square/Acme/Butress Threads – Special forms used in power transmission, jacks, and lead screws.
- 50. FIT OR TOLERANCE CLASS This refers to how tight or loose the thread connection is, depending on tolerance levels: • Class 1 (Loose fit) – Easy assembly and disassembly. • Class 2 (Normal Fit) – General-purpose, most common. • Class 3 (Tight Fit) – High precision, for secure and accurate assemblies.
- 52. PITCH (P) The distance between two adjacent threads. *if threads per inch is known (TPI):
- 53. MAJOR DIAMETER (D) The largest diameter of the thread (outside diameter). *for standard threads (example:M10 x 1.5), the major diameter is the nominal size, * *
- 54. MINOR DIAMTER (d) The smallest diameter (the diameter of the root of the thread). For ISO Metric Threads: Where H is the height of the fundamental triangle:
- 55. PITCH DIAMETER () Diameter at which the thread thickness equals the space between threads. For ISO Metric Threads:
- 56. RULES FOR THREAD CUTTING USING HALFNUT LEVER AND THE THREAD DIAL INDICATOR
- 57. HALF-NUT LEVER Mechanism that locks the carriage to the lead screw for synchronized movement. THREADING DIAL INDICATOR A dial that shows correct moments to re-engage the half- nuts for accurate threading.
- 58. BASIC THREADING STEPS: •Engage half-nut to start threading pass. •Disengage at thread end or when retracting the tool. •Re-engage using TDI at correct mark for alignment.
- 59. TDI RULES: • Even TPI (e.g., 8, 12):Engage on even- numbered lines. • Odd TPI (e.g., 7, 11):Engage on any line. • -TPI divisible by 4 (e.g., 4, 16): Engage on any quarter mark.
- 60. METRIC THREADING • Do not disengage half-nuts between passes. • Use reverse feed for return stroke. • Use metric dial if machine supports it.
- 61. TIPS FOR SUCCESS • Set spindle to low speed. • Angle compound slide at 29.5°. • Make a scratch pass to check pitch. • Use cutting fluid to improve finish.
- 62. QUIZ
- 63. Identification 1.Kafka is a machinist working in a metal fabrication workshop. His client requests a custom lead screw for a manual power press used to shape metal sheets. The lead screw must transfer rotational motion into precise linear motion with minimal friction, since the operator will turn it by hand. Kafka’s supervisor instructs him to manufacture the lead screw on the lathe machine. The screw must handle high axial loads and should offer high efficiency during operation with minimum friction losses. What form of thread should Kafka use ? 2.What helps distribute force between mating threads? 3.What term refers to the measurement that defines the space between threads and the number of threads per inch? 4. Fyodor is asked to solve the diameter at which the thread thickness equals the space between threads. What formula should he use?
- 64. 5.Nowi is a mechanical engineer working for a company that manufactures hydraulic presses used in forming and shaping metal parts. A new client needs a custom press capable of withstanding extremely high axial forces during operation . What form of thread should she use? 6.What does BSPT stand for?
- 65. 7. Arvery works in a mechanical fabrication shop that specializes in building custom lifting equipment. A client has commissioned a manual screw jack for use in heavy-duty maintenance of industrial machinery. The screw jack must use only one continuous helical ridge wraps around the shaft. What type of thread should Arvery use ? 8.What are the three key steps involved in performing a threading operation (in order) ? 9.Give at least one application of a multi-start thread. 10-12. Give at least 3 tips for success in threading. 13-15. Differentiate tapering from threading . Identification
- 66. MODIFIED TRUE OR FALSE Direction: Write TRUE if the statement is correct. If the statement is incorrect, write FALSE, identify what makes the statement wrong, and provide the correct word or phrase. (2 PTS. EACH) 1. On symmetrical threads, the taper thread angle is equal to half of the thread angle. 2. External threads allow an externally threaded component (like a bolt or screw) to be inserted and secured. 3. A taper thread has a gradually decreasing (or increasing) diameter along its height . 4.Chamfer is a spherical shape surface at the end of the thread. 5. Multiple threads run simultaneously and do not overlap.
- 67. PROBLEM SOLVING Marky is designing a 1-inch diameter bolt with 14 threads per inch (TPI) for a high-torque application in a mechanical system. The bolt will be paired with a 1-inch nut, and both need to be manufactured with high precision. For the Thread designation: 1-14 UN (1 inch major diameter, 14 threads per inch). The minor diameter of the bolt is given as 0.900 inches . The nut will be made to fit this bolt, so its minor diameter is 0.920 inches. Draw an illustration based on the problem and write your answers in millimeters. (5pts) a. Calculate the Pitch of the thread. b. Determine the Thread Height of the bolt . c. Calculate the Pitch Diameter for both the bolt and the nut.
- 68. Jan is tasked to design a high-precision acme trapezoidal lead screw for a 3D printer’s Z- axis drive. The screw must have a Trapezoidal thread form 2 cm major diameter , 0.04cm pitch and a measured minor diameter of 1.6 cm . Draw an illustration based on the problem and write your answers in inches . (5 pts. ) Determine the following : a.Pitch and Thread Height b.Major , minor , and the pitch diameter. c. If the lead screw is two-start, what is the lead? PROBLEM SOLVING