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+ color: black; + font-size:small; + padding:0.5em; + margin-bottom:5em; + font-family:sans-serif, serif; +} + + p { + margin-top: .51em; + text-align: justify; + margin-bottom: .49em; + text-indent: 1em; + } + + /* to undo start of para indent */ + .noindent {text-indent: 0;} + .center {text-indent: 0;} + + .right {text-align: right;} + + + .p2 {margin-top: 2em;} + .p4 {margin-top: 4em;} + .pb4 {margin-bottom: 4em;} +.x-ebookmaker .pb4 {margin-bottom: 2em;} + .p6 {margin-top: 6em;} +.x-ebookmaker .p6 {margin-top: 2em;} + + .pad2 {margin-left: 2em;} + .fs75 {font-size: 75%;} + .fs90 {font-size: 90%;} + .fs110 {font-size: 110%;} + .fs120 {font-size: 120%;} + .fs135 {font-size: 135%;} + + .lh15 {line-height: 150%;} + + + .wsp {word-spacing: 0.3em;} + .lspp5 {letter-spacing: 0.05em;} + .wd100 {width: 100%;} + + .hang2 { + text-indent: -2em; + padding-left: 2em; + } + + .pagenum { + position: absolute; + left: 92%; + font-size: small; + text-align: right; + font-style: normal; + font-weight: normal; + font-variant: normal; + text-indent: 0; + color: #A9A9A9 + } /* page numbers */ + + /* Transcriber's notes */ + .transnote { + border: 1px solid; + color: black; + font-size:small; + padding:0.5em; + margin-bottom:5em; + font-family:sans-serif, serif; + } + + .corr { + text-decoration: none; + border-bottom: thin dashed blue;} + + .x-ebookmaker .corr { + text-decoration: none; + border-bottom: none;} + + + /* Illustration classes */ + .illowp50 {width: 50%; max-width:24em;} + .illowp60 {width: 60%; max-width:28em;} + .illowp80 {width: 80%; max-width:35em;} + .illowp100 {width: 100%; max-width:40em;} + + .norm {font-weight: normal;} + .clearx {clear: both;} + + + + </style> +</head> +<body> +<div style='text-align:center'>*** START OF THE PROJECT GUTENBERG EBOOK 76925 ***</div> + +<div class="transnote"> +<strong>TRANSCRIBER’S NOTE</strong> +<p class="noindent">Some minor changes to the text are noted at the end of the book.</p> +</div> + +<hr class="chap x-ebookmaker-drop"> +<div class="chapter"></div> + + <figure class="figcenter illowp60" id="Illustration_COVER" > + <img class="w100" src="images/cover.jpg" alt="Book cover"> + </figure> + <hr class="chap x-ebookmaker-drop"> + + <div class="chapter"></div> + + +<div class="bbx1"> +<div class="bbx2"> +<div class="h1_box"> +<h1> +Elementary Lathe Practice +</h1> +</div> + +<p class="center wsp pb4 fs110"> +AS ADAPTED TO THE TEACHING OF<br> +<br> +<span class="fs135 lspp5">MACHINE SHOP PRACTICE<br> +IN TECHNICAL SCHOOLS.</span><br> +</p> +<hr class="r30"> +<p class="center p2 wsp lh15"> +<span class=fs135>BY T. J. PALMATEER</span><br> +INSTRUCTOR IN MACHINE WORK<br> +<span class=fs90>Leland Stanford Junior University</span><br> +</p> +<hr class="r30 fs90"> +<p class="center wsp"> +Copyright 1917, by T. J. Palmateer<br> +</p> + +<p class="center p6"> +<span class=wsp>FIRST EDITION</span><br> +<br> +<span class=fs120>1917</span><br> +<br> +Press of Nolte Bros. +<img style="max-height: 1.1em; display: inline-block; margin-bottom: -.4em" src="images/pbug.jpg" alt="Union Printer Mark"> + San Jose, California +</p> +</div> +</div> +<hr class="chap x-ebookmaker-drop"> +<div class="chapter"> + <h2 class="nobreak p4" id="PREFACE"> + PREFACE + </h2> +</div> + +<p>The object of this instruction book is to help beginners to +acquire some familiarity with the more common lathe operations +in the shortest practicable period of time. For this purpose three +exercises have been designed with the view of giving the student +the maximum amount of information in the small amount of time +usually allowed for this purpose. The repetition of operations +has therefore been avoided wherever it was considered advisable +and the time lost in simply cutting off metal has been reduced as +much as possible.</p> + +<p>It is assumed that beginners will receive oral instruction on +the manipulation of the lathe, as in shifting the belt, the feed control, +etc. It will also be necessary for the instructor to give a +practical demonstration of most of the operations.</p> + +<p>The lathe speeds for the different operations as indicated in +this book are only approximately correct since the actual cutting +speed of the tool in feet per minute varies with the size and kind +of lathe used. The instructor is expected to designate the proper +speeds although the belt connections given herein will generally +be close enough for beginners.</p> + +<p>In case it is considered advisable to devote to the elementary +lathe operations less time than would be necessary to complete the +three exercises presented herein, very good results can be obtained +if the student will read all of the instructions carefully and +then do only <a href="#EXERCISE_No_1">Exercise No. 1</a> and +<a href="#PIECE_B">piece B of Exercise No. 3.</a></p> + +<p>The instructions here given are not intended as fixed rules for +it is recognized that some of the operations may be done by other +methods with equally good results.</p> + +<p class="right"> + T. J. PALMATEER. +</p> + +<p class="noindent"> + Stanford University, Cal.<br> + <span class="pad2">January 1917.</span> +</p> + +<hr class="chap x-ebookmaker-drop"> +<div class="chapter"> + +<p><span class="pagenum" id="Page_5">[Pg 5]</span></p> + + <h2 class="nobreak" id="EXERCISE_No_1"> + <span class=norm>EXERCISE No. 1.</span> + <br> + <b>FIT SHAFT TO COLLAR—RUNNING FIT</b> + </h2> +</div> + +<figure class="figcenter illowp100" id="ex_1" > + <img class="w100" src="images/ex_1.jpg" alt="Diagram showing machined tube, 6', 3/4 Outer diameter, 13/16 Inner Diameter"> +</figure> + +<p>Cut off with a power hack-saw a piece of steel 6¹⁄₁₆ inches +long from a bar 1 inch in diameter. This will allow ¹⁄₁₆ of an +inch for finishing the ends and ³⁄₁₆ of an inch for turning the +diameter.</p> + +<p>An experienced lathe operator would use a piece of steel ⅝ +of an inch in diameter, but for beginners it is better to use larger +stock to allow for practice turning.</p> + +<h4>CENTERING</h4> + +<p>Center both ends in the centering machine. The size of the +center in this shaft should be from ³⁄₁₆ to ¼ of an inch in +diameter. Larger work should have deeper centers.</p> + +<figure class="figcenter illowp100" id="fig01" > + <img class="w100" src="images/fig01.jpg" alt=""> + <figcaption> + <p>Fig. 1</p> + </figcaption> +</figure> + +<figure class="figcenter illowp100" id="fig02" > + <img class="w100" src="images/fig02.jpg" alt=""> + <figcaption> + <p>Fig. 2</p> + </figcaption> +</figure> + +<figure class="figcenter illowp100" id="fig03_4" > + <img class="w100" src="images/fig03_4.jpg" alt=""> + <figcaption> +<table class="autotable wd100"> +<tr> +<td class="tdc">Fig. 3</td> +<td class="tdc">Fig. 4</td> +</tr> +</table> + </figcaption> +</figure> + +<p><span class="pagenum" id="Page_6">[6]</span></p> + +<p>If a centering machine is not available, the work may be centered +by first locating the center with a pair of dividers and center +punch and then using a combination drill and countersink in +the lathe as shown in <a href="#fig01">Fig. 1</a>. In this case the work is held by +hand to prevent it from turning. As this work is to be turned, it +is necessary to center it only approximately true.</p> + +<p><b>Accurate Centering.</b>—When the work is to be centered accurately, +it may be done by putting one end in the lathe chuck and +the other in a steady rest. A pointed tool is then used in the tool +post as shown in <a href="#fig02">Fig. 2</a>. The point of this tool has an angle of 60 +degrees, the same as the lathe centers, and is ground like a flat +drill so that it cuts on both sides.</p> + +<p>After the shaft is centered with this tool, a center hole about +⅛ of an inch in diameter should be drilled. This is done by +holding the drill in the tail-stock of the lathe with a drill-chuck, +as shown in <a href="#fig03_4">Fig. 3</a>. The object of this center hole is to give the +center of the shaft a bearing on the lathe center a short distance +back from the point, as at A in <a href="#fig03_4">Fig. 4</a>.</p> + +<h4>PLACING WORK IN LATHE</h4> + +<p>The work is made to rotate on the lathe centers by fastening +a lathe dog to the shaft at the head-stock end, as shown at A in +<a href="#fig05">Fig. 5</a>.</p> + +<figure class="figcenter illowp100" id="fig05" > + <img class="w100" src="images/fig05.jpg" alt=""> + <figcaption> + <p>Fig. 5</p> + </figcaption> +</figure> + +<p>The tail-stock center is adjusted so that the shaft will rotate +freely, yet be tight enough to allow no slack, or lost motion. Since +the shaft rotates on this center, it should be kept well lubricated +by using machine oil, or a mixture of graphite and oil.</p> + +<p>To get the best results in turning this sort of work, it is necessary +to face both ends before turning and to rough turn the whole +piece to within about 0.03, or 0.04 of an inch of the finished size +before any part of it is finished. However, it is not always necessary +to do this. The object of first rough turning the shaft all +over is to remove the internal strains of the steel and to wear the +centers down to a good bearing before any finishing cuts are +<span class="pagenum" id="Page_7">[7]</span>taken. The purpose of facing the ends is to get them square, or +true, and smooth.</p> + +<h4>FINISHING END OF SHAFT</h4> + +<p>To face the ends, use a regular turning tool starting to cut +from the outside and feeding by hand towards the center with the +cross feed. Such a tool will leave a ridge near the center, as +shown in <a href="#fig06_7">Fig. 6</a>. This ridge is cut off with a sharp pointed, side +cutting tool, as shown in <a href="#fig06_7">Fig. 7</a>, which is also used for taking the +finishing cut across the whole end of the bar. When taking this +finishing cut, lard oil, or some other lubricant, should be used.</p> + +<figure class="figcenter illowp100" id="fig06_7" > + <img class="w100" src="images/fig06_7.jpg" alt=""> + <figcaption> +<table class="autotable wd100"> +<tr> +<td class="tdc"></td> +<td class="tdc">Fig. 6</td> +<td class="tdc">Fig. 7</td> +</tr> +</table> + </figcaption> +</figure> + +<p>After the finishing cut has been taken, any small ridge, or fin +that remains at the edge of the center is removed by slightly +changing the angle of the tool in the tool post and allowing about +¹⁄₆₄ of an inch play between the centers. Having the work loose +like this when the lathe is running, allows the extreme point of +the side tool to extend beyond the edge of the center and cut a +smooth end.</p> + +<p>The lathe should run slow for the finishing cut and fast when +the regular turning tool is used.</p> + +<h4>TURNING THE SHAFT</h4> + +<p>The first, or roughing cut, is taken with a high-speed steel +tool, or bit, fastened in a tool holder. The tool holder is clamped +in the tool post of the lathe so that the point of the tool is at, or +a little above, the center, or axis, of the lathe, as in <a href="#fig08_10">Fig. 8</a>.</p> + +<p>If the point of the bit is too high, it is easy to see that, as the +shaft rotates, the tool will not cut at all, <a href="#fig08_10">Fig. 9</a>. In case the tool +is set below the center, the cutting action is very poor so that +turning tools are never set as in <a href="#fig08_10">Fig. 10</a>.</p> + +<p><span class="pagenum" id="Page_8">[8]</span></p> + +<figure class="figcenter illowp100" id="fig08_10" > + <img class="w100" src="images/fig08_10.jpg" alt=""> + <figcaption> +<table class="autotable wd100"> +<tr> +<td class="tdc"></td> +<td class="tdc">Fig. 8</td> +<td class="tdc">Fig. 9</td> +<td class="tdc">Fig. 10</td> +</tr> +</table> + </figcaption> +</figure> + +<figure class="figcenter illowp100" id="fig11" > + <img class="w100" src="images/fig11.jpg" alt=""> + <figcaption> + <p>Fig. 11</p> + </figcaption> +</figure> + +<p><b>Speed of the Lathe.</b>—In taking the heavy roughing cuts, the +belt may be placed on the second largest step of the cone, while +for the finishing cuts the lathe should run a little faster, say with +the belt in the next smaller step.</p> + +<p><b>Grinding Turning Tool.</b>—The front, or point, and the sides of +the tool are ground at an angle, which is called the clearance. If +the tool has too little clearance, it will not cut freely, while if it +has too much clearance, the point will be so thin that it will break +off or become dull quickly.</p> + +<p>The top of the tool is also ground at an angle. This is called +the rake. If the tool has too little rake, it will not cut freely and +if it has too much, the edge will soon break down.</p> + +<p>It requires some practice for a beginner to learn the proper +rake and clearance that should be given to a tool. <a href="#fig11">Fig. 11</a> shows +a tool ground with clearance and rake that will give very good +results.</p> + +<p><b>Direction Tool Should Travel.</b>—The depth of the first cut +should be about ¹⁄₁₆ of an inch and the travel of the tool should +always be from the tail-stock end towards the head-stock. If the +travel is in the opposite direction, the pressure on the tail-stock +center is increased, causing it to heat quickly.</p> + +<p>The length of the cut should be as great as possible without +the lathe dog striking the tool, or cross-rest.</p> + +<p><b>Adjusting the Lathe to Turn Straight.</b>—After the first cut, +the work should be calipered and if it is not the same diameter +<span class="pagenum" id="Page_9">[9]</span>at both ends the tail-stock should be adjusted so that the lathe +will turn straight.</p> + +<p>The tail-stock adjustment is made by loosening the main +clamping nut B and one of the screws C and then tightening the +other screw C on the opposite side of the tail-stock, <a href="#fig05">Fig. 5</a>.</p> + +<p>If the shaft is larger at the tail-stock end, the tail-stock should +be moved towards the front of the lathe one half the difference +between the diameters of the shaft at the two ends.</p> + +<p>In doing close work, the tail-stock should be adjusted as +closely as possible, but in this case if it is off center only a little, +say 0.002 or 0.003 of an inch, it will be close enough providing it +is set so that the shaft will be turned larger at the head-stock end. +If the tail-stock is set so that the shaft is turned larger at the tail-stock +end, the shaft will be too small at the other end after the +finishing cut is taken.</p> + +<p><b>Fitting Shaft to the Collar.</b>—After the roughing cut is taken +and the lathe has been adjusted so that it turns approximately +<ins class="corr" title="Transcriber's Note—original text: straght" id="straght">straight</ins>, the end of the shaft is turned for about ¼ of an inch so +that it will just fit the hole in the collar, shown in the drawing +of Exercise 1. To measure this: first set the inside calipers to the +diameter of the hole in the collar, then set the outside calipers to +the inside calipers and caliper the shaft as accurately as possible. +For a final test of this diameter, remove the work from the lathe +and try it with the collar itself.</p> + +<p>The advantage of turning but ¼ of an inch at the end of the +shaft is this; if the finishing cut were set too deep, only ¼ of an +inch of the shaft would be too small, while if this cut were taken +the whole length, the entire shaft would be too small.</p> + +<p>After the shaft has been turned at the end so that it fits the +collar, the rest of the shaft should be turned a little larger, say +0.002 or 0.003 of an inch, in diameter. This will leave enough to +finish with a file.</p> + +<p><b>Filing.</b>—The object of filing is to take out the tool marks, but +it is also found to be much easier to make a close fit by filing off +the last 0.002 or 0.003 of an inch than to take so small a cut with +a tool. The amount of allowance for filing depends upon the +character of the finishing cut. Since the less filing required the +better, the finishing cut should be made as smooth as possible.</p> + +<p>The tool used for the roughing cut may also be used for finishing, +but it is usually necessary to re-sharpen it. After it is reset +in the tool post, the point should be flattened a little wider +<span class="pagenum" id="Page_10">[10]</span>than the pitch of the feed, say about ¹⁄₃₂ of an inch, and parallel +with the work. This is done with an oilstone.</p> + +<p>For filing work on a lathe, a single cut file is used. This is +called a lathe, or mill file.</p> + +<p>The stroke of the file should be slow, steady, and straight +across the shaft. The lathe should run a little faster for filing +than for turning, the object being to have the work make several +revolutions for a single stroke of the file. If the lathe runs too +slow and the stroke of the file is too fast, the shaft, instead of +being filed round, will have a series of flat places on the surface.</p> + +<p>After the work is finished as close to the dog as possible, reverse +it in the lathe and finish that part where the dog was fastened.</p> + +<hr class="chap x-ebookmaker-drop"> +<div class="chapter"> + <h2 class="nobreak" id="EXERCISE_No_2"> + <span class=norm>EXERCISE No. 2.</span> + </h2> +</div> + +<figure class="figcenter illowp100" id="ex_2" > + <img class="w100" src="images/ex_2.jpg" alt="Diagram of tapered shaft, with threads on each end"> +</figure> + +<p>The finished shaft in Exercise No. 1 may be used for Exercise +No. 2.</p> + +<p>Place the shaft in the bench vise and with a rule and scriber +lay off the dimensions: 1¾ in., 3 in., and 1¼ in. Then center +punch the lines just deep enough so that they can be easily seen +when the work is in the lathe.</p> + +<p>Turn the large end first.</p> + +<p>When it is necessary to turn a fixed distance, or to a line as +in this case, it is well to disconnect the feed when the tool is within +about ⅛ of an inch from the end of the cut and to feed the +tool the rest of the distance by hand. If this is not done, the tool +may travel farther than it is intended to.</p> + +<p>It is better to turn the portions to be threaded a little under +rather than over size. For if they are over size, the threads will +not fit the standard size nut, but if under size the threads do not +need to be cut so deep in order to fit the nut.</p> + +<p>For measuring the diameters of this piece set the calipers as +<span class="pagenum" id="Page_11">[11]</span>accurately as possible by measuring from the end of the rule, as +shown in <a href="#fig12_13">Fig. 12</a>.</p> + +<figure class="figcenter illowp100" id="fig12_13" > + <img class="w100" src="images/fig12_13.jpg" alt=""> + <figcaption> +<table class="autotable wd100"> +<tr> +<td class="tdc">Fig. 12</td> +<td class="tdc">Fig. 13</td> +</tr> +</table> + </figcaption> +</figure> + +<p><b>Cutting Recess.</b>—The surface at the end as well as the recesses +between the threads and the taper are cut with a square-nose, or +cutting-off tool, <a href="#fig12_13">Fig. 13</a>.</p> + +<p>This tool <ins class="corr" title="Transcriber's Note—original text: shoull" id="shoull">should</ins> have a sharp smooth edge, the +point being set level with the center of the lathe.</p> + +<p>To produce a smooth finished surface lard oil should be used +with a slow feed and lathe speed.</p> + +<p>After the end is turned to size, reverse the work in the lathe +and turn the other end and the taper before cutting the threads.</p> + +<p><b>Turning Taper.</b>—The drawing calls for a taper of 1 inch per +foot. This is cut by using a taper attachment, or by setting the +tail-stock off center. As most lathes are not provided with a +taper attachment, the latter method will be used.</p> + +<p>If the work was 12 inches long, the tail-stock would be moved +off center ½ inch to turn a taper of 1 inch per foot. It being +only 6 inches long, the tail-stock is set off center but half that +amount, or ¼ inch.</p> + +<p>Before taking the finishing cut, caliper both ends to prove +that the lathe is cutting the correct taper.</p> + +<h4>THREAD CUTTING</h4> + +<p>The threads are cut to fit ½ inch and ⅝ inch nuts having +United States Standard threads. These threads are flattened at +the top and bottom to the amount of ⅛ of the pitch instead of +being sharp pointed as in the case of Standard V-threads.</p> + +<p><b>Pitch.</b>—The pitch of the thread is the distance from the center +of one thread to the center of the one adjoining. On the end of +the exercise having 13 threads per inch the pitch is ¹⁄₁₃ of an +inch so that the width of the flat at the top and bottom of this +<span class="pagenum" id="Page_12">[12]</span>thread should be ⅛ of ¹⁄₁₃ of an inch, or about .009 of an inch.</p> + +<p><b>Lead.</b>—The lead of the thread is the distance a nut on the +screw will travel in making one complete turn. For single threads +the pitch and lead are the same, but for double threads the lead +is twice the pitch.</p> + +<p><b>Grinding Tool.</b>—The sides of U. S. S. threads form an angle of +60 degrees. To cut this thread in a lathe, a tool the same shape as +the threads is used. A gauge for grinding this tool accurately is +shown in <a href="#fig14_16">Fig. 14</a>.</p> + +<figure class="figcenter illowp100" id="fig14_16" > + <img class="w100" src="images/fig14_16.jpg" alt=""> + <figcaption> +<table class="autotable wd100"> +<tr> +<td class="tdc">Fig. 14</td> +<td class="tdc">Fig. 15</td> +<td class="tdc">Fig. 16</td> +</tr> +</table> + </figcaption> +</figure> + +<p>If a U. S. S. thread gauge is not available, the tool can be +ground with the aid of a regular thread and center gauge, shown +in <a href="#fig14_16">Fig. 15</a>. With such a gauge the angle can be ground accurately, +but it will be necessary to measure the flat point with a rule.</p> + +<p>The top of the tool should be ground so that it will be approximately +in a horizontal plane when set in the lathe.</p> + +<p>Where the thread to be cut is as fine as 13 per inch the flat +surface at the point of the tool is so small that the extreme point +can be oil-stoned off instead of being taken off with the grinding +wheel. The flat point should never be wider than the standard +size, but if it is a little too narrow it will make very little difference +in ordinary lathe work.</p> + +<p><b>Setting Tool.</b>—To set the tool so that both sides of the thread +will have the same angle, the thread gauge is used as shown in +<a href="#fig14_16">Fig. 16</a>. The tool should be set on a level with the center of the +lathe.</p> + +<p><b>How Lathe is Geared.</b>—To cut 13 threads per inch the work +must make 13 revolutions while the carriage, which carries the +tool, travels one inch. For this purpose the lathe spindle is connected +<span class="pagenum" id="Page_13">[13]</span>to the lead screw with the proper size gears and the lead +screw to the carriage by a split nut. This split nut is back of the +carriage apron and is opened and closed by the lever E, <a href="#fig17">Fig. 17</a>.</p> + +<figure class="figcenter illowp100" id="fig17" > + <img class="w100" src="images/fig17.jpg" alt=""> + <figcaption> + <p>Fig. 17</p> + </figcaption> +</figure> + +<figure class="figright illowp50" id="fig18" > + <img class="w100" src="images/fig18.jpg" alt=""> + <figcaption> + <p>Fig. 18</p> +</figcaption> +</figure> + <p class="noindent lh15"> + A. Index Plate<br> + B. Stud Gear<br> + C. Screw Gear<br> + D. Intermediate or Idle Gear<br> + E. Lever for connecting Carriage to Lead Screw<br> + J. Lever for Disconnecting and Reversing Feed<br> + K. Adjustable Stop for Thread Cutting</p> + + <p class="clearx">If the lead screw of the lathe has 6 threads per inch, the gearing + to cut 13 threads per inch must have the same ratio as 6 is to + 13. To cut 16 threads the ratio would be 6 to 16.</p> + <p>It is not necessary to figure the size of gears for the different + <span class="pagenum" id="Page_14">[14]</span>threads as all lathes are provided with an index plate that designates + the proper size gears to be placed on the stud B and screw + C, <a href="#fig17">Fig. 17</a>, for the desired thread.</p> + <p><b>To Set Change Gear.</b>—To change these gears, first loosen the + nuts holding the stud and screw gears B and C. Next loosen the + nut G. This will allow the intermediate gear to drop away from + the stud gear B. Then loosen the nut H so that the intermediate + gear can be drawn back away from the gear on the lead screw C.</p> + <p>When the gears are put together, they should be set so that + there will be a little slack, or lost motion, between the different + gears. If they are set too close together, they will make a great + deal of noise when running and there is also danger of breaking + the teeth.</p> + <p>While all lathes are not designed alike the method of changing + the gears is very much the same on all machines except those having + the quick change-gear device. With a lathe having such a device, + instead of changing the gears on the stud and screw the same + result is obtained by shifting a combination of levers.</p> + <p><b>Why Feed Should Be Disconnected.</b>—The mechanism that + controls the feed, or travel, of the tool when cutting threads is + independent of that used for the feed when doing plain turning. + The two feeds usually run at different speeds so that if they are + both in action at the same time the gears in the carriage will + break. For this reason all lathes are provided with some means + of disconnecting the feed used for plain turning when cutting + threads.</p> + <p>To disconnect the feed on the lathe shown in <a href="#fig17">Fig. 17</a>, move the + lever J to the central, or neutral, position. This should always + be done before starting to cut the threads.</p> + <p><b>Speed of Lathe.</b>—The lathe should run slower for cutting + threads than for plain turning. With most lathes if the belt is + on the largest step of the cone it will give about the right speed + for cutting the threads in this exercise.</p> + <p>The object of running the lathe slow is to give the operator + time to draw back the tool at the end of the cut and to obtain a + smoother cut. If the speed of the lathe is too fast, the cutting + action will be so quick that the tool, instead of cutting clean and + smooth, will tear out the metal leaving a rough surface.</p> + <p>The slower the lathe runs the easier it is to cut the threads, + but it will also take longer to do the job. It therefore requires + <span class="pagenum" id="Page_15">[15]</span>practical experience to determine the proper speed to be used for + cutting the different size threads.</p> + <p><b>Chamfering.</b>—After the lathe and tool are properly set, chamfer + off the sharp corners where the threads begin and end with + the side of the thread tool. The depth of this cut should be about + the same as that of the threads when finished. If the corners are + not chamfered, the threads, when cut, will form a very thin edge, + or fin, at the ends.</p> + <p><b>Use of Adjustable Stop.</b>—To regulate the depth of each cut + an adjustable stop is used as shown at K. First move the tool so + that the point just touches the work, then adjust the screw on + the attachment K so that the cross-rest will not go in any farther. + Now move the carriage by hand until the point of the tool is a + little past the tail-stock end of the work; close the split nut on + the lead screw with the lever E; and turn the screw on the attachment + K so that the tool can be moved in just enough to take + a very light cut.</p> + <p>Start the lathe and when the tool has reached the end of the + cut back it out and reverse the lathe. By reversing the lathe the + tool is returned to the starting point without disconnecting any + of the gearing. The object of drawing the tool back is to prevent + it from dragging on the work during its return.</p> + <p>The tool will never travel over the same path on the reverse + as on the forward movement of the lathe on account of the slack, + or lost motion, in the gears.</p> + <p>This first cut is taken to prove that the lathe is properly + geared, so the work should be measured with a rule, or screw + pitch gauge.</p> + <p>Adjust the screw at K until the tool can be moved in deeper + for the next cut and repeat the operation until the thread is + nearly finished. Then the tool should be reset so that it will cut + on only one side at a time.</p> + <p><b>Finishing Side of Thread.</b>—When roughing out the threads, + the tool cuts on both sides of the point since it is fed straight into + the work. It is much easier, though, to finish the threads smooth + if the tool cuts on one side only. This is done by rapping the end + of the tool holder so that it is turned in the tool post just enough + to change the position of the point of the tool about .01, or .02 of + an inch.</p> + <p>To prove that the tool is set over the proper amount, turn the + <span class="pagenum" id="Page_16">[16]</span>lathe forward by hand a few revolutions, to take out all the slack, + or lost, motion in the gears, then move the tool into the groove of + the thread until one side just touches the side of the thread. The + other side of the tool should then be about .01, or .02 of an inch + away from the side of the thread.</p> + <p>After the tool is properly adjusted, set the stop K. The tool + is then drawn back and the lathe reversed until the tool is at the + end of the work ready for a cut. It usually requires several finishing + cuts to take out all the rough marks left by the roughing + cuts.</p> + <p>When this side of the thread is finished, the other side is finished + in the same manner.</p> + <p>If the lathe is provided with a compound rest, a somewhat + different procedure is usually followed since the rest can be set + at an angle of 30 degrees with the work, as in <a href="#fig18">Fig. 18</a>.</p> + <p>In this case the tool is moved in by turning the small hand-crank + M until the side at O has been cut to the proper depth. + While making these first cuts, the stop K is merely used to bring + the cross-rest to the same position each time. The tool is then + drawn back slightly with the hand-crank M and the stop K adjusted + so that the tool can be moved straight in by means of the + hand-crank Q. This will finish the other side of the thread at P.</p> + <p>To determine when the thread is cut to the proper size the + work is removed from the lathe and tested with a standard nut + having U. S. S. threads.</p> + <p>After the threads are cut on this end of the exercise, it is reversed + in the lathe and the other end threaded in a similar manner.</p> + <p>To prevent the screw of the dog from marring the portion + already threaded two nuts should be screwed on and the dog fastened + to the nuts.</p> + <p><b>How to Reset the Tool.</b>—When cutting threads of this size and + larger, the tool usually becomes dull from taking the heavy roughing + cuts. It is then necessary to resharpen it before taking the + fine finishing cuts.</p> + <p>To reset the tool in the lathe first get the angles correct, as + shown in <a href="#fig14_16">Fig. 16</a>. Then revolve the lathe forward by hand to + take up the slack in the gears and move the tool in close to the + threads. If the tool is in a position so that it will cut too much + off one side of the thread, it may be changed by disengaging the + reversing gears with the lever R and turning the lathe by hand. + <span class="pagenum" id="Page_17">[17]</span>When the tool is in the proper position relative to the groove of + the thread, the reverse gear lever R is reset.</p> + <p>In a case where the tool is off the desired position only a very + little, it may be corrected by the rapping process.</p> + <p>If the lathe has a compound rest the tool may be brought to + the correct position by turning the hand-crank M.</p> + <p>It would be well for beginners to practice thread cutting on a + piece of scrap steel before trying to cut them on the exercise.</p> + + +<hr class="chap x-ebookmaker-drop"> + <div class="chapter"> + <h2 class="nobreak" id="EXERCISE_No_3"> + <span class=norm>EXERCISE No. 3.</span> + <br> + CAST IRON FINISHED ALL OVER. + </h2> + </div> + + +<figure class="figcenter illowp80" id="ex_3"> + <img class="w100" src="images/ex_3.jpg" +alt="Two piece, outer casing with inside threads, and inner mandrel with threads."> +</figure> + <p class="noindent hang2"><b>Sequence of Operations</b>:<br> + 1. Finish the inside of Piece A.<br> + 2. Drill and Ream the hole in Piece B.<br> + 3. Mount B on mandrel and finish outside.<br> + 4. Screw A on B and finish the outside of A.</p> + +<h3 id="PIECE_A" class="nosep">Piece A.</h3> + +<figure class="figcenter illowp100" id="fig19_20" > + <img class="w100" src="images/fig19_20.jpg" alt=""> + <figcaption> + +<table class="autotable wd100"> +<tr> +<td class="tdc">Fig. 19 Rough Casting</td> +<td class="tdc">Fig. 20 Finished Casting</td> +</tr> +</table> + <p class="fs75">10 Thrds. per 1″ U. S. S.</p> + </figcaption> +</figure> + +<p><span class="pagenum" id="Page_18">[18]</span></p> + +<h4>USE OF 4-JAW CHUCK.</h4> + +<p>To machine the inside of piece A it is necessary to hold it in +the lathe by means of an independent four-jaw chuck, as shown +in <a href="#fig21">Fig. 21</a>. Work of this kind is usually chucked so that the outside +surfaces will be within ¹⁄₃₂ of an inch of running true.</p> + +<figure class="figcenter illowp100" id="fig21" > + <img class="w100" src="images/fig21.jpg" alt=""> + <figcaption> + <p>Fig. 21</p> + </figcaption> +</figure> + +<p>The process of chucking the work is as follows:</p> + +<p><b>Centering Work in the Chuck.</b>—Place the work in the chuck +and adjust the jaws until they are all at approximately equal +distances from the circles on the face of the chuck. Then put a +cutting-off tool loosely in the tool post and move it close to the +work and as near as possible to the end of the chuck jaws. Revolve +the lathe by hand to prove if the work is centered. If it is +not centered to within ¹⁄₃₂ of an inch, readjust the jaws until it +is. Now move the cutting-off tool to the end of the work and +turn the lathe by hand. If the end runs out of true, rap it with a +hammer at such points as will correct its position.</p> + +<p><b>Advantage of Proper Chucking.</b>—<a href="#fig21">Fig. 21</a> shows the work held +by the middle step of the cone. One reason for holding it in this +way is to permit the rough turning of the larger step while in +the chuck. If the work were held by the small end, it would be +apt to work loose when taking the heavy roughing cuts on account +of the distance that the work projects out and the small diameter +on which the chuck grips compared with that of the large end +which is to be turned.</p> + +<h4>ROUGH TURNING AND BORING.</h4> + +<p>After the work has been properly chucked, rough turn the +end and the largest diameter to within ¹⁄₃₂ of an inch of the finished +size.</p> + +<p>All cast iron has a hard surface, or scale, from ¹⁄₆₄ to ¹⁄₃₂ +of an inch deep so that it is necessary to run the lathe slower +for the first cut than for those made after the scale has been removed. +<span class="pagenum" id="Page_19">[19]</span>In taking this first cut the tool should be set deep +enough to permit the point to cut under the scale.</p> + +<p><b>Speed of Lathe.</b>—The speed of the lathe in taking the roughing +cut on work of this size should be about right if the belt is on +the smallest step of the cone and the back gears are used. After +the scale is removed, the lathe may be run faster.</p> + +<p>A beginner will require experience before being able to determine +the proper speeds and feeds for the <ins class="corr" title="Transcriber's Note—original text: diffrent" id="diffrent">different</ins> kinds of +lathe work.</p> + +<p><b>Advantage of Roughing Inside.</b>—As the inside of piece A must +fit the outside of the piece B, the 1⅛ inch hole, the threads, +and the taper must be machine true with each other, or else A will +not fit into B properly. Now if the taper should be finished and +the work moved in the chuck before the threads and the 1⅛ +inch hole are finished, they would not be true with each other. +For this reason it would be well to rough bore the inside to within +¹⁄₃₂ of an inch of the finished size before any of these three parts +are finished.</p> + +<p><b>Roughing Inside.</b>—To rough bore the taper use a regular turning +tool. Set the compound rest to the correct angle and feed the +tool in at that angle.</p> + +<p>If the lathe is not provided with a compound rest, the taper +may be rough bored by turning both feeds by hand and following +the cored surface as closely as possible.</p> + +<p>The cored hole in the rough casting, <a href="#fig19_20">Fig. 19</a>, is ¹⁵⁄₁₆ of an +inch in diameter which allows ³⁄₁₆ of an inch for finishing the +1⅛ inch hole and ⁵⁄₁₆ for the portion where the threads are to +be cut.</p> + +<p><b>Use of Flat Drill.</b>—To rough bore the hole a 1¹⁄₁₆ flat, or +lathe, drill is used as shown in <a href="#fig21">Fig. 21</a>. The holder A is clamped +in the tool post so that the slot in it will hold the drill at the center +of the lathe. If the drill is held above or below the center, the +hole will be drilled larger than the drill. To prove that the slot +in the holder is at the center, move it close to the tail-stock center. +After the holder is properly set, move it as close to the work as +possible and feed the drill into the exercise by turning the hand-crank +on the tail-stock.</p> + +<p>This drill removes the hard surface, or scale, and also trues +up, or centers, the hole to within ¹⁄₆₄, or ¹⁄₃₂ of an inch. Now +enlarge the portion of the hole where the threads are to be cut +with a 1³⁄₁₆ drill.</p> + +<p><span class="pagenum" id="Page_20">[20]</span></p> + +<p>To determine when this drill has been fed in far enough, mark +on the drill with a piece of chalk the distance from the end of the +work to the point where the recess is to be cut. By sighting +across the end of the work the operator can then see when the +drill has been fed in the proper distance.</p> + +<p><b>Use of Boring Bar.</b>—To cut the square shoulder where the +threads begin and the recess where they end, use a tool and boring +bar, as shown in <a href="#fig22">Fig. 22</a>, held in the tool post. The width of this +tool is ⁵⁄₃₂ of an inch so that it will be necessary to take two cuts +to make the recess wide enough. Such a narrow tool is used because +it is less liable to chatter.</p> + +<figure class="figcenter illowp100" id="fig22" > + <img class="w100" src="images/fig22.jpg" alt=""> + <figcaption> + <p>Fig. 22</p> + </figcaption> +</figure> + +<p>This tool is ground with clearance at the sides as well as at +the front and it should also be noticed that it is wider at the cutting +edge than back close to the boring bar. This is done so that +when the tool is fed into the work there will be little, or no chance +of its binding on the side.</p> + +<p>To obtain the correct setting for the tool, move the boring bar +into the hole and bring it up close to one side. The tool should +then be adjusted until its cutting edge is parallel to the elements +of this surface.</p> + +<p>The work is now all roughed out so that it makes very little +difference which of the three fitting parts is finished first.</p> + +<h4>FINISHING INSIDE</h4> + +<p>The 1⅛ inch hole has been drilled with a ¹¹⁄₁₆ inch lathe +drill, but as such a tool cannot be relied upon to drill true to center, +or size, it is necessary to turn it out with a boring tool. With +<span class="pagenum" id="Page_21">[21]</span>this tool the hole can be bored true to center and within .01 of an +inch of the finished size.</p> + +<p>The boring bar used in this case is the same as shown in +<a href="#fig22">Fig. 22</a>, but the cutter has a rounded point and is similar to the tool +used for outside turning except that it is ground with less clearance.</p> + +<p>To insure accuracy and conserve time, the hole is then finished +with a shell reamer held in the lathe as shown in <a href="#fig23">Fig. 23</a>.</p> + +<figure class="figcenter illowp100" id="fig23" > + <img class="w100" src="images/fig23.jpg" alt=""> + <figcaption> + <p>Fig. 23</p> + </figcaption> +</figure> + +<p><b>Reaming the Hole.</b>—Before starting the reamer, the hole +should be bored at the end, for a distance of about ⅛ of an inch, +to the size which will just permit the reamer to enter. This diameter +must be calipered very carefully and should be tested with +the reamer itself. The rest of the hole is then bored about .01 of +an inch smaller in diameter to allow enough material for finishing +with the reamer. Since the reamer used in this case cuts on +the sides as well as on the end, the hole must be bored true to center +in order to be reamed true.</p> + +<p>If the reamer has a tapered shank, it is held in the lathe by a +square shank socket and wrench, as shown in <a href="#fig23">Fig. 23</a>, and is fed +into the work by turning the hand-crank on the tail-stock.</p> + +<figure class="figcenter illowp100" id="fig24" > + <img class="w100" src="images/fig24.jpg" alt=""> + <figcaption> + <p>Fig. 24</p> + </figcaption> +</figure> + +<p>In case the reamer has a straight shank, it is held as shown in +<a href="#fig24">Fig. 24</a>. Here a dog is fastened to the end of the reamer and prevented +from turning by a tool clamped at an angle in the tool post. +The end of the tool presses against the dog near the shank +of the reamer so that as the reamer is fed into the work the carriage +of the lathe is forced along with it. This causes the tool +<span class="pagenum" id="Page_22">[22]</span>to hold the end of the reamer against the center of the tail-stock.</p> + +<p>When reaming work in a lathe, if the tail-stock is off center +the hole will be reamed too large at the front end.</p> + +<p><b>Accurate Boring with Boring Bar.</b>—In turning out holes with +a boring bar, if all the cuts are started from one end, that end will +be bored larger than the other. In case the hole is to be reamed, +the reamer will correct this, but if the hole is to be finished with +the boring bar it will be necessary to bore the hole from both ends. +This is done by reversing the feed of the carriage.</p> + +<p><b>Speed of Lathe.</b>—The speed of the lathe for reaming should be +slower than when using the boring bar. If the belt is on the second +smallest step of the cone with the back gears in, the lathe +should have about the right speed for reaming. When using the +boring bar, the belt should be on the largest step of the cone without +the back gear.</p> + +<h4>INSIDE THREADING</h4> + +<p>The inside threads are cut in very much the same manner as +the outside ones. The cutting tool is held in the boring bar and, +like all boring tools, is ground with less clearance than tools used +for outside work.</p> + +<p>To regulate the depth of each cut, the screw in the adjustable +stop is placed between the stop and the cross-rest. Then by turning +the screw in after a cut has been taken the cross-rest can be +drawn back to permit a deeper cut with the tool.</p> + +<p><b>Cause of Threads Breaking.</b>—When cutting threads in cast +iron, they will break if the roughing cuts are too heavy and are +liable to if they are cut to a sharp point. Another cause for the +breaking of cast iron threads is the use of a dull tool, or one with +too little clearance.</p> + +<p><b>Finishing Threads.</b>—As a general rule cast iron is machined +without using a lubricant, but in finishing threads a little lard oil +will aid in producing a smooth finish.</p> + +<h4>FINISHING ENDS</h4> + +<p>The end of the work may be finished by taking a very light +cut with the turning tool and then scraping it with a lathe scraper, +<span class="pagenum" id="Page_23">[23]</span>as shown in <a href="#fig25_26">Fig. 25</a>. To provide a rest for the scraper a tool +is clamped in the tool post and as close as possible to the surface +being scraped.</p> + +<figure class="figcenter illowp100" id="fig25_26" > + <img class="w100" src="images/fig25_26.jpg" alt=""> + <figcaption> +<table class="autotable wd100"> +<tr> +<td class="tdc">Fig. 25</td> +<td class="tdc">Fig. 26</td> +</tr> +</table> + </figcaption> +</figure> + +<p>A scraper is usually made from an old file ground smooth on +the two sides and with a little clearance at the end.</p> + +<h4>FINISHING TAPER</h4> + +<p>To finish the taper, set the compound rest at an angle of 30 +degrees with the axis of the lathe. Such a rest is normally at +right angles with the lathe axis so that it must be turned through +60 degrees to cut the 30 degree angle. A regular turning tool +may be used to finish this angle, but it should be set so that the +straight side will be nearly parallel with the tapered surface.</p> + +<p>If the lathe is not provided with a compound rest, the angle +may be cut with the side of a tool set at the proper angle. To set +this tool, use the thread and center gauge, as shown in <a href="#fig25_26">Fig. 26</a>.</p> + +<p>In case the angle is any other than 30, or 60 degrees, it is +necessary to set the tool with a bevel and bevel protractor.</p> + +<p>After the taper has been cut, it may be finished smooth by +scraping with a lathe scraper in very much the same manner as +shown in <a href="#fig25_26">Fig. 25</a>. The tool that is used as a rest is set in as close +as possible to the taper. If this rest is too far away from the surface +being finished, the scraper will chatter leaving a rough surface.</p> + +<p><span class="pagenum" id="Page_24">[24]</span></p> +<h3 id="PIECE_B" class="nosep">Piece B.</h3> + + +<figure class="figcenter illowp100" id="fig27" > + <img class="w100" src="images/fig27.jpg" alt=""> + <figcaption> + +<table class="autotable wd100"> +<tr> +<td class="tdc">Rough Casting</td> +<td class="tdc">Fig. 27</td> +<td class="tdc">Finished Casting</td> +</tr> +</table> +<p class="fs75">10 Thrds. per 1″ U. S. S.</p> + </figcaption> +</figure> + +<h4>DRILLING AND REAMING.</h4> + +<p>This piece is first placed in the chuck, as shown in <a href="#fig28">Fig. 28</a>, +and the end rough turned to see if it is a good casting. The hole +is then drilled with a ²³⁄₃₂ inch twist drill and reamed out to +size with a ¾ inch rose reamer.</p> + +<figure class="figcenter illowp100" id="fig28" > + <img class="w100" src="images/fig28.jpg" alt=""> + <figcaption> + <p>Fig. 28</p> + </figcaption> +</figure> + +<p><b>Centering Twist Drill.</b>—This drill will not bore a hole in the +center unless the point is controlled in some way. To do this, a +cutting-off tool is clamped in the tool post with its point well +above the center of the lathe and is then moved close to the point +of the drill. As the drill starts to cut, it wabbles a little on account +of the point being off center. The cutting-off tool is then +gradually brought against the drill which is at the same time being +slowly fed into the work by turning the hand-crank on the +tail-stock. It is necessary to have the drill centered true before it +begins to cut the full diameter.</p> + +<p>The drill should be placed in the tail-stock so that the cutting +edges are vertical. If they are horizontal, it will be difficult to +make the drill center.</p> + +<p>If the hole in this piece were larger, it would be cast with a +core and then machined in the same manner as the 1⅛ inch hole +in piece A, but since it is cast solid, the hole can be machined +more advantageously by using a twist drill and a rose reamer.</p> + +<p><b>Reaming.</b>—After the hole has been drilled with the ²³⁄₃₂ +<span class="pagenum" id="Page_25">[25]</span>drill, bore it out with a small boring tool for about ⅛ of an inch +from the end to the diameter that will just fit over the reamer +and insure its starting true. Ream the hole with the reamer held +in the same manner as the twist drill in <a href="#fig28">Fig. 28</a>.</p> + +<p><b>Speed of Lathe.</b>—The lathe should run slower for reaming +than for drilling. The speed will be about right for this size +reamer if the belt is on the largest step of the cone without the +back gears being used. The speed for the drill may be much +faster. With a high-speed steel drill, the belt can be run on the +second smallest step of the cone. If the drill is made of carbon +steel, a slower speed should be used.</p> + +<p><b>Advantage of Rose Reamer.</b>—In drilling long holes like this, +the drill is very apt to get off center a little as it is fed deeper into +the work, even though it may have been started dead true.</p> + +<p>The reamer used in this case is called a rose reamer, or rose +bit, and cuts on the end only. For this reason, if the hole is approximately +true, say within ¹⁄₆₄ of an inch, it will ream the hole +straight and true to size if it is once started true.</p> + +<h4>FINISHING CORNER</h4> + +<p>After the hole is bored and reamed, the work may be finished +at the end by using a tool ground like a threading tool, but having +an angle at the point a little less than 90 degrees, as in +<a href="#fig29">Fig. 29</a>.</p> + +<figure class="figcenter illowp60" id="fig29" > + <img class="w100" src="images/fig29.jpg" alt=""> + <figcaption> + <p>Fig. 29</p> + </figcaption> +</figure> + +<p>The boss, or hub, which is 1⅜ inches in diameter, is finished +with one cutting edge of this tool set nearly parallel to the work, +the point being a trifle deeper than the rest. This will insure the +full depth of cut for the entire length and also a good sharp corner. +The direction of feed for this tool should be from the end +and towards the square corner or shoulder. If it is fed in the opposite +direction the tool is apt to chatter.</p> + +<p>This tool is also used to finish the end, but it is turned a little +<span class="pagenum" id="Page_26">[26]</span>in the tool post so that the other cutting edge is nearly parallel +to the surface to be cut. After using this tool, the work may be +finished smoother by scraping the ends, as in <a href="#fig25_26">Fig. 25</a>, and by filing +the boss, or hub.</p> + +<h4>USE OF MANDREL, OR ARBOR</h4> + +<p>Before this piece can be finished on the outside, it must be +forced on a mandrel, or arbor, and placed in the lathe, as shown +in <a href="#fig30">Fig. 30</a>. Most commercial shops are provided with hardened +steel mandrels for this purpose, but if one is not available it can +be made from soft steel in the following manner:</p> + +<figure class="figcenter illowp100" id="fig30" > + <img class="w100" src="images/fig30.jpg" alt=""> + <figcaption> + <p>Fig. 30</p> + </figcaption> +</figure> + +<p><b>Making Mandrel.</b>—Cut off a piece of steel of suitable length, +say 6 inches, and rough turn it to within ¹⁄₃₂ of an inch of the +diameter of the hole. Then turn it at the end for a distance of +about ⅛ of an inch to the size that will just fit the hole. The +rest of the distance is now turned .002, or .003 of an inch larger +and filed for about 3 inches until it will just fit the hole. The +next 2 inches are filed with a slight taper so that when the mandrel +is pressed into the hole it will fit tight enough to hold the +casting while it is being turned. This kind of a fit is called a +forced, or driving fit.</p> + +<p>When making such a mandrel, it is not necessary to turn that +portion to which the dog is fastened.</p> + +<p><b>Mounting Work on Mandrel.</b>—Before pressing the mandrel in, +it should be oiled to prevent it from being marred, or scored. +Mandrels are usually forced in with a mandrel press, but if one +is not available, they may be driven in with a hammer. When +this method is used, a piece of lead, or some other soft material, +must be held on the end of the mandrel to keep the hammer from +marring the center.</p> + +<h4>FINISHING OUTSIDE OF PIECE B TO FIT A</h4> + +<p>This casting is rough turned to within ¹⁄₃₂ of an inch of the +finished size before any part of it is finished. The 1⅛ inch end +is then turned until it fits the corresponding part of the hole in +<span class="pagenum" id="Page_27">[27]</span>piece A as closely as possible and yet not so tight that it cannot +be freely rotated. This kind of a fit is called a close running fit.</p> + +<p><b>Cutting Threads.</b>—The portion to be threaded should be +turned a little smaller than the diameter at the bottom of the +threads in piece A. This size is measured by means of the inside +spring-thread calipers.</p> + +<p>There is no recess, or groove, cut at the end of this thread so +that if the threading tool is allowed to travel farther than the end +of the preceding cut, either the point of the tool or the threads +may break. To prevent this, the lathe is stopped when the tool is +within a half a thread of the end and the cut finished by turning +the lathe by hand. In this way the lathe is kept under control +and the tool may be drawn back when it reaches the end of the +preceding cut. Experienced lathe operators do not, as a rule, +turn the lathe by hand, but control the lathe entirely by the +shipper.</p> + +<p>The speed of the lathe for cutting this thread will be about +right for beginners if the belt is on the second smallest step of the +cone and the back gears are thrown in.</p> + +<p><b>Finishing the Angle, or Taper.</b>—The 30 degree angle may be +cut by setting the compound rest to the correct angle and using a +regular turning tool. In case the tool leaves a few tool marks, +they may be removed by filing.</p> + +<p>If the lathe is not provided with a compound rest, this angle +may be cut by setting a square-nose tool, as in <a href="#fig31">Fig. 31</a>, with the +aid of a thread gauge. Any other angle would have to be set +with a bevel and bevel protractor.</p> + +<figure class="figcenter illowp60" id="fig31" > + <img class="w100" src="images/fig31.jpg" alt=""> + <figcaption> + <p>Fig. 31</p> + </figcaption> +</figure> + +<p>This tool is not as wide as the surface to be cut because one +that will cut the full width is very liable to chatter. It is therefore +better to make several cuts with a narrow tool. The surface +can then be finished smooth by filing.</p> + +<p>The closeness of the fit of this taper with that in A can be +<span class="pagenum" id="Page_28">[28]</span>tested by rubbing black paint, which consists of lamp black and +oil, on the tapered surface in A. When B is screwed into A, +marks will be made on B indicating the high spots. If these are +not too high, they may be removed by filing.</p> + +<h4>FINISHING OUTSIDE OF PIECE A.</h4> + +<p>Piece A may now be screwed on B and the outside rough +turned to within ¹⁄₃₂ of an inch of the finished size.</p> + +<p>The ends of the different steps are finished to the proper +length with the tool shown in <a href="#fig29">Fig. 29</a>. This same tool can then be +used to turn the different diameters to within 0.002 or 0.003 of an +inch of the required size. These steps are brought to the final +size by filing.</p> + +<p><b>Filing.</b>—The file for this work should be less than 1 inch in +width. If it is wider than the steps, a beginner will usually file +the portion at the end of each step smaller in diameter than that +which is close to the square corners.</p> + +<p>The different diameters may be measured accurately with the +micrometer calipers.</p> + +<h4>KNURLING</h4> + +<p>After piece A is finished, it is removed from B and B is reversed +in the lathe so that the boss may be knurled.</p> + +<p>In case there is enough room between the dog and the work, +when held as in <a href="#fig30">Fig. 30</a>, there is no need to reverse the work for +knurling since it can be done in this position.</p> + +<p>The boss at the end of B is used as a handle so that if it were +left smooth it would be hard to turn by hand. The surface is +therefore made rough with a knurling tool as shown in <a href="#fig32">Fig. 32</a>.</p> + +<figure class="figcenter illowp100" id="fig32" > + <img class="w100" src="images/fig32.jpg" alt=""> + <figcaption> + <p>Fig. 32</p> + </figcaption> +</figure> + +<p>The speed of the lathe should be about the same for knurling +as for thread cutting. If the lathe runs too fast, the knurling tool +does not cut satisfactorily.</p> + +<p>The tool is set so that the face of the rollers is parallel with +<span class="pagenum" id="Page_29">[29]</span>the surface to be knurled. When starting the cut, the rollers can +be forced into the piece easier if about half of their width extends +past the end of the work.</p> + +<p>The knurling tool should be pressed into the work fast enough +so that about one half the depth of the finished knurl will be cut +while the lathe makes three or four revolutions. If the tool is +forced in too slow, it will cut a finer knurled surface than the +rollers are intended to cut.</p> + +<p>The tool is fed along the surface in the same manner as in +plain turning. The speed at which the carriage of the lathe moves +has no effect upon the pitch of the knurled surface since this is +controlled by the pitch of the grooves in the rollers. If a finer +knurled surface is desired, a knurling tool having rollers with +finer grooves would have to be used.</p> + +<hr class="chap x-ebookmaker-drop"> + +<div class="chapter"> +<div class="transnote"> +<strong>TRANSCRIBER’S NOTE</strong> + +<p class="noindent">Illustrations in this eBook have been positioned between paragraphs +and outside quotations. </p> + +<p class="noindent">Obvious typographical errors and punctuation errors have been +corrected after careful comparison with other occurrences within +the text and consultation of external sources.</p> + +<p class="noindent">Some hyphens in words have been silently removed, some added, +when a predominant preference was found in the original book.</p> + +<p class="noindent">Except for those changes noted below, all misspellings in the text, +and inconsistent or archaic usage, have been retained.</p> + +<table class="autotable"> +<tr> +<td class="tdl">Pg <a href="#straght">9</a>:</td> +<td class="tdl">‘straght’ replaced with ‘straight’</td> +</tr> +<tr> +<td class="tdl">Pg <a href="#shoull">11</a>:</td> +<td class="tdl">‘shoull’ replaced with ‘should’</td> +</tr> +<tr> +<td class="tdl">Pg <a href="#diffrent">19</a>:</td> +<td class="tdl">‘diffrent’ replaced with ‘different.’</td> +</tr> +</table> +</div> +</div> +<div style='text-align:center'>*** END OF THE PROJECT GUTENBERG EBOOK 76925 ***</div> +</body> +</html> + |