Manual Machining Training

Class Information
Tooling U-SME classes are offered at the beginner, intermediate, and advanced levels. The typical class consists of 12 to 25 lessons and will take approximately one hour to complete.
Class Name:Threading on the Engine Lathe 235
Description:This class describes the manual lathe components used for threading and explains how to cut and inspect an external and internal thread.
Prerequisites: 150205  150225 
Number of Lessons:14
Language:English, Spanish
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Class Outline
  • Objectives
  • Threading on the Manual Lathe
  • Types of Threads
  • Measured Parts of a Thread
  • Unified Threads
  • Metric Threads
  • Lathe Components for Threading
  • Sample Thread Specification
  • Cutting an External Thread: Pre-Machining
  • Cutting an External Thread: Threading Setup
  • Cutting an External Thread: Cutting the Thread
  • Cutting an External Thread: Inspecting the Thread
  • Cutting an Internal Thread
  • Summary
Class Objectives
  • Describe threading on the manual lathe.
  • Match each common thread characteristic with its description.
  • Identify the measured parts of a thread.
  • Identify the characteristics of a Unified thread specification.
  • Identify the characteristics of a metric thread specification.
  • Describe the lathe components specifically used for threading.
  • Describe the steps necessary to prepare for cutting a thread.
  • Describe the pre-machining operations performed on the part prior to threading.
  • Describe how to setup the threading components on the lathe prior to threading.
  • Describe how to cut an external thread.
  • Describe common inspection methods used to inspect an external thread.
  • Describe how to cut an internal thread.

Class Vocabulary

Vocabulary TermDefinition
allowance A specific amount of clearance or interference between threads.
blade micrometer A type of micrometer with flattened tips on the anvil and spindle. It is primarily used to measure narrow external grooves. Undercut is often measured with a blade micrometer.
bolt A threaded cylindrical device used for fastening parts. Bolts usually have blunt ends and mate with a nut.
center gage A type of gage used to set the threading tool bit perpendicular to the workpiece.
chamfer A small, angled surface added on the end of a shaft, around the opening of a hole, or along an edge. A chamfer removes the sharp edge and helps remove burrs.
class of fit A system that designates how loose or tight the thread should be in general.
clearance An amount of space or distance between two objects.
crest The top where two flanks meet on a thread.
depth The length of the distance between the root and crest of the thread. Depth is also known as the height of the thread.
end gears A set of controls on the quick-change gearbox that transmit power from the lathe spindle to the leadscrew.
external thread A type of thread formed on the outside of a cylinder, such as on bolts and screws.
feed change lever A lever on the apron that is used to select one of three types of feed: longitudinal feed, cross feed, or threading feed.
flank An angled side of the body of a thread that connects the root to the crest.
go gage A gage on or in which a good part should fit easily.
half-nut lever A lever attached to the side of the apron that is engaged when the line on the threading dial matches up with the proper reference mark. The half-nut lever is only used in threading operations.
included angle The angle created by two adjacent flanks of a thread.
interference A tight fit designed where the smallest permissible shaft is larger than the largest permissible hole.
internal thread A type of thread formed in holes, such as in nuts.
ISO metric thread A standard thread form based on millimeters that was developed for use in Europe.
leadscrew The long, threaded device that controls the precise movement of the carriage on a lathe.
left-hand thread A type of thread that is screwed in by rotating it counterclockwise. Left-hand threads are rare.
major diameter The distance between the crests of an OD thread or the roots of an ID thread. Major diameter is the widest diameter on a thread.
metric designation The letter "M" that is at the beginning of all metric thread designations.
minor diameter The distance between the roots of an OD thread and the crests of an ID thread. Minor diameter is the smallest diameter on a thread.
no go gage A gage on or in which a good part should not fit.
nominal diameter The overall diameter of the part. Nominal diameter is one of the parts of a metric thread specification.
nominal size The size by which something is known, which may be different from its actual, measurable size.
nut A block, usually of metal, with a threaded hole that mates with a bolt. The outer shape of a nut is often six-sided.
pitch The distance from one thread groove to the next measured from crest to crest. For inch-based threads, pitch is expressed as "1" over the number of threads per inch. For metric threads, pitch is expressed in millimeters.
pitch diameter The measured distance between the pitch points taken in the groove between the threads. Pitch diameter is one of the most important dimensions in thread inspection.
plug gage A hardened, cylindrical gage used to inspect the size of a hole. Plug gages are available in standardized diameters.
quick-change gearbox A set of controls mounted to the front of the lathe bed that engages the leadscrew to drive the carriage for turning operations.
right-hand thread A type of thread that is screwed in by rotating it clockwise. Most fasteners have right-hand threads.
root The base where two flanks meet on a thread.
screw A threaded device used for fastening parts or transferring motion. Screws usually have pointed ends.
thread A long, spiraling groove that is machined into a workpiece. Threads are essential for the creation of fasteners.
thread cutting A method of producing screw threads that generally uses a single-point tool to cut a blank or workpiece as it rotates on a lathe.
thread micrometer A U-shaped measuring instrument with a V-shaped anvil and a cone-shaped spindle used to measure threads.
thread ring gage A disk of heavy metal with a central, threaded hole made to match a particular OD thread. The gage is screwed onto the part being inspected as though the two are mating parts.
thread series A thread designation that identifies the coarseness or fineness of threads.
threading dial A rotating dial with lines and numbers that is used to precisely set the leadscrew and carriage positions in relationship to the workpiece. The threading dial allows the lathe to repeatedly return to the exact same position.
threading/grooving tool A type of single-point tool fitted with a tool bit used for threading and/or grooving operations.
threads per inch The decimal equivalent of the number of threads in an inch.
tolerance class A number and letter combination that indicates the degree of fit and whether it is an internal or external thread.
undercut A groove machined at the end of a thread. Undercut is a visual reference that indicates the end of the thread.
Unified thread A standard thread form based on inches that was developed by the U.S., Canada, and Great Britain.