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Tag Archives: lathe advance

THREAD FORM BASICS

Transmitting (translating) screw threads are used primarily to transmit or impart power or motion to a mechanical part.Often, these transmitting screws are of multiple lead to effect rapid motion. Bench vises and house jacks are familiar applications of single-lead transmitting screws. The lead screw on a lathe and the table feed screws on milling machines …

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STEADY REST

On a lathe, long shafts tend to vibrate when cuts are made, leaving chatter marks. Even light finish cuts will often produce chatter when the shaft is long and slender. To help eliminate these problems, use a steady rest to support workpieces that extend from a chuck more than four or five diameters …

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BASIC EXTERNAL THREAD MEASUREMENT

The simplest method for checking a thread is to try the mating part for fit. The fit is determined solely by feel with no measurement involved. Although a loose, medium, or close fit can be determined by this method, the threads cannot be depended on for interchangeability with others of the same size and …

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CUTTING THE THREAD

The following is the procedure for cutting right-hand threads: Step 1: Move the tool off the work and turn the crossfeed micrometer dial back to zero. Step 2: Feed it in .002 in. on the compound dial. Step 3: Turn on the lathe and engage the half-nut lever (Figure I-310). Step 4: Take a …

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SETTING UP FOR THREADING

Begin setup by obtaining or grinding a tool for cutting Unified threads of the required thread pitch. The only difference in tools for various pitches is the flat on the end of the tool. For Unified threads this is .125P, as discussed in Unit 10. If the toolholder you are using has no back rake, no grinding …

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HOW THREADS ARE CUT ON A LATHE

Threads are cut on a lathe with a single-point tool by taking a series of cuts in the same helix of the thread. This is sometimes called chasing a thread.A direct ratio exists between the headstock spindle rotation, the lead screw rotation, and the number of threads on the lead screw. This ratio can be …

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UNIFIED AND AMERICAN NATIONAL FORMS

The American National form (Figure I-290) is now obsolete and has evolved into the Unified form (Figure I-291). The basic geometry of the two systems is similar. Taps and dies are marked with letter symbols to designate the series of the threads they form. For example, the symbol for American Standard taper pipe thread is NPT, …

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DRIVES

Most modern lathes have gear drives; some are direct drive and some variable. One drive system uses a variable-speed drive (Figure I-131) with a high and low range using a back gear. On this drive system, the motor must be running to change the speed on the varidrive, but the …

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LATHE SPINDLE NOSE

The lathe spindle nose is the carrier of a variety of workholding devices fastened to it in several ways. The spindle is hollow and has an internal Morse taper at the nose end,which makes possible the use of taper shank drills or drill chucks (Figure I-107). This internal taper is also used to hold live centers, drive centers, …

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CUTTING TOOL GEOMETRY

On a lathe, metal is removed from a workpiece by turning it against a single-point cutting tool. This tool must be hard and should not lose its hardness from the heat generated by machining. High-speed steel is used for many tools, as it fulfills these requirements and is easily shaped by grinding. For this reason …

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