The Starrett Book for Machinists' Apprentices

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L. S. Starrett Company, 1917 - Machine-shop practice - 184 pages

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Page 144 - A Circle is a plane figure bounded by a curved line every point of which is equally distant from a point within called the center.
Page 149 - A sphere is a solid bounded by a curved surface, every point of which is equally distant from a point within called the center.
Page 167 - The above assumes that the lathe is geared 1:1; that is, the lathe screw constant is equal to the number of threads per inch on the lead screw. If the lathe is not so geared, the lathe screw constant should be used in place of the threads per inch on the lead screw. The foregoing example shows how the figuring can be done when the gears are on the spindle stud and lead screw; but the problem is usually one of finding out what gears to use. Suppose 7 threads are to be cut, and there are 5 threads...
Page 31 - ... provided for holes, which ordinary standard reamers can produce, in two grades. Classes A and B, the selection of which is a question for the user's decision and dependent upon the quality of the work required ; some prefer to use Class A as working limits and Class B as inspection limits.
Page 52 - A feed per revolution of .004 to .007 for drills }A inch and smaller, and from .007 to .015 for larger is about all that should be required. This feed is based on a peripheral speed of a drill equal to : 30 feet per minute for steel ; 35 feet per minute for iron ; 60 feet per minute for brass. It may also be found advisable to vary the speed somewhat according as the material to be drilled is more or less refractory. We believe that these speeds should not be exceeded under ordinary circumstances....
Page 153 - ... balance, the product of the weight and length of weight arm is equal to the product of the power and length of power arm. When the fulcrum is between the weight and the force...
Page 140 - For the purpose of measuring angles, the circumference is divided into 360 equal parts, called degrees; each degree into 60 equal parts, called minutes; each minute into 60 equal parts, called seconds.
Page 22 - To read the tool, note how many inches, tenths (or .100) and fortieths (or .025) the 0 mark on the vernier is from the 0 mark on the bar; then note the number of divisions on the vernier from 0 to a line which exactly coincides with a line on the bar.
Page 43 - ... of different grades. Turkish emery is a hard black and brown stone found in Turkey and brought to this country for use in machine shops. Its quality, for hardness and durability in mechanical work, has never been excelled in any stone yet found. The cloth made is of various grades of coarseness. " The numbers representing the grades of emery run from 8 to 120, and the degree of smoothness of surface they leave may be compared to that left by files as follows : .8 and 10 represent the cut of a...
Page 16 - In the human hand the sense of touch is most prominent in the fingertips. Therefore, the contact measuring tool should be held by the fingers only, and in such a way as to bring it in contact with the finger-tips. If the tool is harshly grasped by the fingers, the sense of touch or "feel" is much reduced. For this reason the tool should be delicately and lightly held instead of gripped tightly. While it is possible to transfer by "feel" a length with an error not exceeding one-quarter of one-thousandth...

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