Read Ebook: Turning and Boring A specialized treatise for machinists students in the industrial and engineering schools and apprentices on turning and boring methods including modern practice with engine lathes turret lathes vertical and horizontal boring machines by Jones Franklin Day

Font size: 10 px 15 px 20 px 25 px 30 px 35 px

Background color: BlackWhiteGrayLight GrayDark GrayDim Gray

Text color: BlackWhiteGrayLight GrayDark GrayDim Gray

Apply/Save settings

Ebook has 175 lines and 101573 words, and 4 pages

PAGES

THE ENGINE LATHE--TURNING AND BORING OPERATIONS

General Description of an Engine Lathe--Example of Cylindrical Turning--Facing the Ends Square with a Side-tool--Turning Tool--Turning Work Cylindrical--Roughing and Finishing Cuts--Filing and Finishing--Aligning Centers for Cylindrical Turning--Application of Drivers or Dogs--Lathe Arbors or Mandrels--Different Types of Lathe Arbors--Mandrel or Arbor Press--Steadyrest for Supporting Flexible Parts--Application of Steadyrest when Boring--The Follow-rest--Centering Parts to be Turned--Centering Machine--Different Forms of Centers--Precaution When Centering Tool Steel--Facing the Ends of Centered Stock--Truing Lathe Centers--Universal, Independent and Combination Chucks--Application of Chucks--Example of Boring--Measuring Bored Holes--Setting Work in the Chuck--Inaccuracy from Pressure of Chuck Jaws--Drilling and Reaming--Holding Work on Faceplate--Application of Angle-plate to Faceplate--Supporting Outer End of Chucked Work--Boring Large Castings in the Lathe--Boring Holes to a Given Center Distance--Turning Brass, Bronze and Copper--Machining Aluminum 1-53

LATHE TURNING TOOLS AND CUTTING SPEEDS

Turning Tools for General Work--Tool-holders with Inserted Cutters--The Position of Turning Tools--Tool Grinding--Shape or Contour of Cutting Edge--Direction of Top Slope for Turning Tools--Clearance for the Cutting Edge--Angle of Tool-point and Amount of Top Slope--Grinding a Lathe Tool--Cutting Speeds and Feeds--Average Cutting Speeds for Turning--Factors which Limit the Cutting Speed--Rules for Calculating Cutting Speeds--Feed of Tool and Depth of Cut--Effect of Lubricant on Cutting Speed--Lubricants Used for Turning--Lard Oil as a Cutting Lubricant 54-79

TAPER TURNING--SPECIAL OPERATIONS--FITTING

Setting Tailstock Center for Taper Turning--Example of Taper Turning--Setting the Tailstock Center with a Caliper Tool--Setting the Tailstock Center with a Square--The Taper Attachment--Application of Taper Attachment--Height of Tool when Turning Tapers--Taper Turning with the Compound Rest--Accurate Measurement of Angles and Tapers--To Find Center Distance for a Given Taper--To Find Center Distance for a Given Angle--To Find Angle for Given Taper per Foot--To Find Angle for Given Disk Dimensions--Use of the Center Indicator--Locating Work by the Button Method--Eccentric Turning--Turning a Crankshaft in a Lathe--Special Crankshaft Lathe--Operation of Special Crankshaft Lathe--Spherical Turning--Spherical Turning Attachments--Turning with Front and Rear Tools--A Multiple-tool Lathe--Examples of Multiple Turning--Knurling in the Lathe--Relieving Attachment--Application of Relieving Attachment--Relieving Hobs or Taps Having Spiral Flutes--Classes of Fits Used in Machine Construction--Forced Fits--Allowance for Forced Fits--Pressure for Forced Fits--Allowance for Given Pressure-Shrinkage Fits 80-134

THREAD CUTTING IN THE LATHE

Selecting the Change Gears for Thread Cutting--The Thread Tool--Cutting the Thread--Indicator or Chasing Dial for Catching Threads--Principle of the Thread Indicator--Replacing Sharpened Thread Tool--Use of Compound Rest for Thread Cutting--Threads Commonly Used--Multiple Threads--Cutting a U. S. Standard Thread--Cutting a Left-hand Thread--Cutting a Square Thread--Cutting Multiple Threads--Setting Tool When Cutting Multiple Threads--Taper Threading--Internal Threading--Stop for Thread Tools--The Acme Standard Thread--The Whitworth Thread--Worm Threads--Coarse Threading Attachment--Testing the Size of a Thread--The Thread Micrometer--Three-wire System of Measuring Threads--Rivett-Dock Threading Tool--Cutting Screws to Compensate for Shrinkage--Calculating Change Gears for Thread Cutting--Lathes with Compound Gearing--Fractional Threads--Change Gears for Metric Pitches--Quick Change-gear Type of Lathe 135-177

TURRET LATHE PRACTICE

General Description of a Turret Lathe--Example of Turret Lathe Work--Machining Flywheels in Turret Lathe--Finishing a Flywheel at One Setting in Turret Lathe--Finishing a Webbed Flywheel in Two Settings--Tools for Turret Lathes--Box-tools--Examples of Box-tool Turning--Hollow Mills--Releasing Die and Tap Holders--Self-opening Die Heads--Collapsing Taps--Miscellaneous Turret Lathe Tools--Turning Gasoline Engine Pistons in Turret Lathe--Turning Piston Rings in Turret Lathe--Piston Turning in Pratt and Whitney Turret Lathe--Attachment for Turning Piston Rings--Turning Worm-gear Blanks in Turret Lathe--Turning Bevel Gear Blanks--Shell Turning Operation in Flat Turret Lathe--Chuck Work in Flat Turret Lathe--Double-spindle Flat Turret Lathe--Automatic Chucking and Turning Machine--Example of Work on Automatic Turning Machine--Determining Speed and Feed Changes--Setting the Turret Slide--Setting the Cross-slide Cam--Setting the Boring Tool for Recessing--Adjustments for Automatic Feed and Speed Changes--Turning Flywheel in Automatic Chucking and Turning Machine--Automatic Multiple-spindle Chucking Machine--Selecting Type of Turning Machine 178-241

VERTICAL BORING MILL PRACTICE

Boring and Turning in a Vertical Boring Mill--Holding and Setting Work on Boring Mill Table--Turning in a Boring Mill--Boring Operations--Turning Tools for the Vertical Boring Mill--Turning a Flywheel on a Vertical Mill--Convex Turning Attachment for Boring Mills--Turning Taper or Conical Surfaces--Turret-lathe Type of Vertical Boring Mill--Examples of Vertical Turret Lathe Work--Floating Reamer Holders--Multiple Cylinder Boring Machine 242-274

HORIZONTAL BORING MACHINES

Horizontal Boring Machine with Vertical Table Adjustment--Drilling and Boring--Cutters Used--Cutter-heads for Boring Large Holes--Cylinder Boring--Boring a Duplex Gasoline Engine Cylinder--Examples of Boring, Radial Facing and Milling--Fixture for Cylinder Lining or Bushing--Horizontal Boring Machine of Floor Type 275-297

INDEX 299-307

TURNING AND BORING

THE ENGINE LATHE--TURNING AND BORING OPERATIONS

The standard "engine" lathe, which is the type commonly used by machinists for doing general work, is one of the most important tools in a machine shop, because it is adapted to a great variety of operations, such as turning all sorts of cylindrical and taper parts, boring holes, cutting threads, etc. The illustration Fig. 1 shows a lathe which, in many respects, represents a typical design, and while some of the parts are arranged differently on other makes, the general construction is practically the same as on the machine illustrated.

It is very difficult to file a part smooth and at the same time to keep it round and cylindrical, and the more filing that has to be done, the greater the chance of error. For this reason, the amount left for filing should be very small; in fact, the metal removed by filing should be just enough to take out the tool marks and give a smooth finish. Very often a satisfactory finish can be obtained with a turning tool, and filing is not necessary at all. The file generally used for lathe work is a "single-cut bastard" of "mill" section, having a length of from 12 to 14 inches.

Sometimes particles of metal collect between the teeth of a file and make deep scratches as the file is passed across the work. When this occurs, the teeth should be cleaned by using a wire brush or a file card, which is drawn across the file in the direction of the teeth. This forming of tiny particles between the teeth is known as "pinning" and it can sometimes be avoided by rubbing chalk on the file. Filing is not only done to obtain a smooth finish, but also to reduce the work to an exact diameter, as a very slight reduction can be made in this way.

Most cylindrical parts can be finished more quickly and accurately in the grinder than in the lathe, and many classes of work are, at the present time, simply rough-turned in the lathe and then ground to size in a cylindrical grinding machine.

Straight dogs are also made with two driving ends which engage pins on opposite sides of the faceplate. This type is preferable because it applies the power required for turning, evenly to the work, which still further reduces the tendency to spring it out of shape. The principal objection to the double-ended type lies in the difficulty of adjusting the driving pins so that each bears with equal pressure against the dog. The double-ended driver is often used for large work especially if deep roughing cuts are necessary.

Particular care should be taken to preserve the accuracy of the centers of lathe arbors by keeping them clean and well-oiled while in use.

Some shops are equipped with power-driven mandrel or arbor presses. This type is particularly desirable for large work, owing to the greater pressure required for inserting mandrels that are comparatively large in diameter. One well-known type of power press is driven by a belt, and the downward pressure of the ram is controlled by a handwheel. The ram is raised or lowered by turning this handwheel in one direction or the other, and a gage shows how much pressure is being applied. This type of press can also be used for other purposes, such as forcing bushings or pins into or out of holes, bending or straightening parts, or for similar work.

Work mounted on the faceplate is generally set true by some surface before turning. As the hole in this casting should be true with the round boss, the casting is shifted on the faceplate until the rough outer surface of the boss runs true; the clamps which were previously set up lightly are then tightened. The face e is first turned by using a round-nosed tool. This tool is then replaced by a boring tool and the hole is finished to the required diameter. If the hole being bored is larger than the central hole in the faceplate, the casting should be clamped against parallel pieces, and not directly against the faceplate, to provide clearance for the tool when it reaches the inner end of the hole and prevent it from cutting the faceplate. The parallel pieces should be of the same thickness and be located near the clamps to prevent springing the casting.

Sometimes it is rather difficult to hold heavy pieces against the vertical surface of the faceplate while applying the clamps, and occasionally the faceplate is removed and placed in a horizontal position on the bench; the work can then be located about right, and after it is clamped, the faceplate is placed on the lathe spindle by the assistance of a crane.

Special faceplate jaws, such as the one shown to the right in Fig. 33, can often be used to advantage for holding work on large faceplates. Three or four of these jaws are bolted to the faceplate which is converted into a kind of independent chuck. These faceplate jaws are especially useful for holding irregularly shaped parts, as the different jaws can be located in any position.

Fig. 46 shows how the lining illustrated in Fig. 45 is bored in a large engine lathe. The casting is held in special fixtures which are attached to the lathe carriage, and the boring-bar is rotated by the lathe spindle. The tool-head of this boring-bar carries two tools located 180 degrees apart and it is fed along the bar by a star-feed mechanism shown attached to the bar and the tailstock spindle. Each time the bar revolves, the star wheel strikes a stationary pin and turns the feed-screw which, as the illustration shows, extends along a groove cut in one side of the bar. This feed-screw passes through a nut attached to the tool-head so that the latter is slowly fed through the bore. When using a bar of this type, the carriage, of course, remains stationary.

Cylindrical parts attached to the carriage can also be bored by using a plain solid bar mounted between the centers. The bar must be provided with a cutter for small holes or a tool-head for larger diameters and the boring is done by feeding the carriage along the bed by using the regular power feed of the lathe. A symmetrically shaped casting like a bushing or lining is often held upon wooden blocks bolted across the carriage. These are first cut away to form a circular seat of the required radius, by using the boring-bar and a special tool having a thin curved edge. The casting is then clamped upon these blocks by the use of straps and bolts, and if the curved seats were cut to the correct radius, the work will be located concentric with the boring-bar. When using a boring-bar of this type, the bar must be long enough to allow the part being bored to feed from one side of the cutter-head to the other, the cutter-head being approximately in a central location.

The speed for turning soft brass is much higher than for steel, being ordinarily between 150 and 200 feet per minute. When turning phosphor, tobin or other tough bronze compositions, the tool should be ground with rake the same as for turning steel, and lard oil is sometimes used as a lubricant. The cutting speed for bronzes varies from 35 or 40 to 80 feet per minute, owing to the difference in the composition of bronze alloys.

Turning tools for copper are ground with a little more top rake than is given steel turning tools, and the point should be slightly rounded. It is important to have a keen edge, and a grindstone is recommended for sharpening copper turning tools. Milk is generally considered the best lubricant to use when turning copper. The speed can be nearly as fast as for brass.

The following information on this subject represents the experience of the Brown-Lipe Gear Co., where aluminum parts are machined in large quantities: For finishing bored holes, a bar equipped with cutters has been found more practicable than reamers. The cutters used for machining 4-inch holes have a clearance of from 20 to 22 degrees and no rake or slope on the front faces against which the chips bear. The roughing cutters for this work have a rather sharp nose, being ground on the point to a radius of about 3/32 inch, but for securing a smooth surface, the finishing tools are rounded to a radius of about 3/4 inch. The cutting speed, as well as the feed, for machining aluminum is from 50 to 60 per cent faster than the speeds and feeds for cast iron. The lubricant used by this company is composed of one part "aqualine" and 20 parts water. This lubricant not only gives a smooth finish but preserves a keen cutting edge and enables tools to be used much longer without grinding. Formerly, a lubricant composed of one part of high-grade lard oil and one part of kerosene was used. This mixture costs approximately 30 cents per gallon, whereas the aqualine and water mixture now being used costs less than 4 cents per gallon, and has proved more effective than the lubricant formerly employed.

LATHE TURNING TOOLS AND CUTTING SPEEDS

The different tools referred to in the foregoing might be called the standard types because they are the ones generally used, and as Fig. 2 indicates, they make it possible to turn an almost endless variety of forms. Occasionally some special form of tool is needed for doing odd jobs, having, perhaps, an end bent differently or a cutting edge shaped to some particular form. Tools of the latter type, which are known as "form tools," are sometimes used for finishing surfaces that are either convex, concave, or irregular in shape. The cutting edges of these tools are carefully filed or ground to the required shape, and the form given the tool is reproduced in the part turned. Ornamental or other irregular surfaces can be finished very neatly by the use of such tools. It is very difficult, of course, to turn convex or concave surfaces with a regular tool; in fact, it would not be possible to form a true spherical surface, for instance, without special equipment, because the tool could not be moved along a true curve by simply using the longitudinal and cross feeds. Form tools should be sharpened by grinding entirely on the top surface, as any grinding on the end or flank would alter the shape of the tool.

While tools must, of necessity, be varied considerably in shape to adapt them to various purposes, there are certain underlying principles governing their shape which apply generally; so in what follows we shall not attempt to explain in detail just what the form of each tool used on the lathe should be, as it is more important to understand how the cutting action of the tool and its efficiency is affected when it is improperly ground. When the principle is understood, the grinding of tools of various types and shapes is comparatively easy.

A turning tool for brass or other soft metal, particularly where considerable hand manipulation is required, could advantageously have a clearance of twelve or fourteen degrees, as it would then be easier to feed the tool into the metal; but, generally speaking, the clearance for turning tools should be just enough to permit them to cut freely. Excessive clearance weakens the cutting edge and may cause it to crumble under the pressure of the cut.

Experiments conducted by Mr. F. W. Taylor to determine the most efficient form for lathe roughing tools showed that the nearer the lip angle approached sixty-one degrees, the higher the cutting speed. This, however, does not apply to tools for turning cast iron, as the latter will work more efficiently with a lip angle of about sixty-eight degrees. This is doubtless because the chip pressure, when turning cast iron, comes closer to the cutting edge which should, therefore, be more blunt to withstand the abrasive action and heat. Of course, the foregoing remarks concerning lip angles apply more particularly to tools used for roughing.

Often a tool which has been ground properly in the first place is greatly misshapen after it has been sharpened a few times. This is usually the result of attempts on the part of the workman to re-sharpen it hurriedly; for example, it is easier to secure a sharp edge on the turning tool shown to the left in Fig. 12, by grinding the flank as indicated by the dotted line, than by grinding the entire flank. The clearance is, however, reduced and the lip angle changed.

There is great danger when grinding a tool of burning it or drawing the temper from the fine cutting edge, and, aside from the actual shape of the cutting end, this is the most important point in connection with tool grinding. If a tool is pressed hard against an emery or other abrasive wheel, even though the latter has a copious supply of water, the temper will sometimes be drawn. When grinding a flat surface, to avoid burning, the tool should frequently be withdrawn from the stone so that the cooling water can reach the surface being ground. A moderate pressure should also be applied, as it is better to spend an extra minute or two in grinding than to ruin the tool by burning, in an attempt to sharpen it quickly. Of course, what has been said about burning applies more particularly to carbon steel, but even self-hardening steels are not improved by being over-heated at the stone. In some shops, tools are ground to the theoretically correct shape in special machines instead of by hand. The sharpened tools are then kept in the tool-room and are given out as they are needed.

Cutting Speeds and Feeds for Turning Tools

Cutting speeds for tools of a good grade of high-speed steel, properly ground and heat-treated.--From MACHINERY'S HANDBOOK.

Ordinary machine steel is generally turned at a speed varying between 45 and 65 feet per minute. For ordinary gray cast iron, the speed usually varies from 40 to 50 feet per minute; for annealed tool steel, from 25 to 35 feet per minute; for soft yellow brass, from 150 to 200 feet per minute; for hard bronze, from 35 to 80 feet per minute, the speed depending upon the composition of the alloy. While these speeds correspond closely to general practice, they can be exceeded for many machining operations.

The most economical speeds for a given feed and depth of cut, as determined by the experiments conducted by Mr. F. W. Taylor, are given in the table, "Cutting Speeds and Feeds for Turning Tools." The speeds given in this table represent results obtained with tools made of a good grade of high-speed steel properly heat-treated and correctly ground. It will be noted that the cutting speed is much slower for cast iron than for steel. Cast iron is cut with less pressure or resistance than soft steel, but the slower speed required for cast iron is probably due to the fact that the pressure of the chip is concentrated closer to the cutting edge, combined with the fact that cast iron wears the tool faster than steel. The speeds given are higher than those ordinarily used, and, in many cases, a slower rate would be necessary to prevent chattering or because of some other limiting condition.

When the cutting speed is too high, even though high-speed steel is used, the point of the tool is softened to such an extent by the heat resulting from the pressure and friction of the chip, that the cutting edge is ruined in too short a time. On the other hand, when the speed is too slow, the heat generated is so slight as to have little effect and the tool point is dulled by being slowly worn or ground away by the action of the chip. While a tool operating at such a low speed can be used a comparatively long time without re-sharpening, this advantage is more than offset by the fact that too much time is required for removing a given amount of metal when the work is revolving so slowly.

Generally speaking, the speed should be such that a fair amount of work can be done before the tool requires re-grinding. Evidently, it would not pay to grind a tool every few minutes in order to maintain a high cutting speed; neither would it be economical to use a very slow speed and waste considerable time in turning, just to save the few minutes required for grinding. For example, if a number of roughing cuts had to be taken over a heavy rod or shaft, time might be saved by running at such a speed that the tool would have to be sharpened when it had traversed half-way across the work; that is, the time required for sharpening or changing the tool would be short as compared with the gain effected by the higher work speed. On the other hand, it might be more economical to run a little slower and take a continuous cut across the work with one tool.

The experiments of Mr. Taylor led to the conclusion that, as a rule, it is not economical to use roughing tools at a speed so slow as to cause them to last more than 1-1/2 hour without being re-ground; hence the speeds given in the table previously referred to are based upon this length of time between grindings. Sometimes the work speed cannot be as high as the tool will permit, because of the chattering that often results when the lathe is old and not massive enough to absorb the vibrations, or when there is unnecessary play in the working parts. The shape of the tool used also affects the work speed, and as there are so many things to be considered, the proper cutting speed is best determined by experiment.

in which

For example if a cutting speed of 60 feet per minute is wanted and the diameter of the work is 5 inches, the required speed would be found as follows:

If the diameter is simply multiplied by 3 and the fractional part is omitted, the calculation can easily be made, and the result will be close enough for practical purposes. In case the cutting speed, for a given number of revolutions and diameter, is wanted, the following formula can be used:

Machinists who operate lathes do not know, ordinarily, what cutting speeds, in feet per minute, are used for different classes of work, but are guided entirely by past experience.

Share on: WhatsApp @Hash Facebook Tweet