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CNC Technology

CUTTING MULTIPLE-LEAD THREADS

Several methods are used for indexing or dividing multiplelead threads. One method is to use an accurately slotted face plate (Figure I-410). The lathe dog is moved 180 degrees for two leads, 120 degrees for three leads, and 90 degrees for four leads. This method will work only on external threading. Another method is …

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MULTIPLE-LEAD THREADS

Multiple threads, though not often used, are usually found on industrial machines, valves, fire hydrants, and aircraft landing gear. They are also used on jars and other containers. Most screws and bolts have single-lead threads, which are formed by cutting one groove with a single-point tool.A double-lead thread has two grooves, a triple-lead thread …

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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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FOLLOWER REST

Long, slender shafts tend to spring away from the tool, vary in diameter, chatter, and often climb the tool. To prevent these problems when machining a slender shaft along its entire length, a follower rest (Figure I-396) is often used. Follower rests are bolted to the carriage and follow along …

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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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METHODS OF MEASURING TAPERS

The most convenient and simple way of checking tapers is to use the taper plug gage (Figure I-367) for internal tapers and the taper ring gage (Figure I-368) for external tapers. Some taper gages have go and no-go limit marks on them (Figure I-369). To check an internal taper, first …

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OFFSET TAILSTOCK METHOD

Long, slight tapers may be produced on shafts and external parts between centers. Internal tapers cannot be made by this method. Power feed is used, so good finishes are obtainable. Because most lathes are equipped with taper attachments, the offset tailstock method is seldom used now. Its greatest advantage is that longer tapers can …

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METHODS OF MAKING A TAPER

There are several methods of turning a taper on a lathe: the compound slide method, the offset tailstock method, the taper attachment method, the use of a form tool, and the use of a tracer or CNC lathe. Each method has its advan- tages and disadvantages, so the kind of …

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USE OF TAPERS

Tapers are used on machines because of their capacity to align and hold machine parts and to realign them when they are repeatedly assembled and disassembled. This repeatability assures that tools such as centers in lathes, taper shank drills in drill presses, and arbors in milling machines will run in perfect alignment when placed in …

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BASIC INTERNAL THREAD MEASUREMENT

Because small internal threads are most often made by tap- ping, the pitch diameter and fit are determined by the tap used. However, internal threads cut with a single-point tool need to be checked. A precision thread plug gage (Figure I-342) is generally sufficient for most purposes. These gages are available in various sizes, which …

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