How to Grind Lathe Tool Cutter Bits

How to Grind Lathe Tool Cutter Bits - South Bend Lathe Works / Правильная заточка токарных резцов [1938, PDF]

Год выпуска: 1938

Язык: английский

Автор: South Bend Lathe Works

Издательство: SOUTH BEND LATHE WORKS

Формат: PDF

Качество: Отсканированные страницы

Количество страниц: 16

Цена: 800 рублей

Описание: Bulletin No. 35 Modern Shop Practice for Grinding Lathe Tool Cutter Bits

1 he cutting tool is one of the most important things to consider in the machining of metal in the lathe. In order to machine metal accurately and efficiently it is important that the cutter bit have a keen cutting edge, ground with the correct clearance, rake, etc., for the particular kind of metal being machined, and that the cutter bit be set at the correct height.

In this booklet the latest shop practice for grinding various types of lathe tool cutter bits is outlined. The methods shown are used in our own shop, where we operate 150 Back-Geared, Screw Cutting Lathes on all kinds of machine work.

The cutter bit is that part of the lathe tool which cuts the metal that must be removed to bring the work to the desired size and shape. The cutter bit is usually made of high speed steel and held in a lathe tool holder as shown in Fig. 2 at the top of the page.

High speed steel cutter bits are hardened and are ready for use when properly ground. Fig. 3 at the right shows an unground cutter bit and Fig. 4 shows the same cutter bit after grinding. In I ig. 5 the cutter bit is shown mounted in the lathe tool holder, ready for use.

Correct grinding of the lathe tool cutter bit is essential for good lathe work, because a properly ground cutter bit will produce better results, last longer and cut more freely than one improperly ground.

I he forged steel tool holder as shown at the top of the page is made in three types, straight, right hand, and left hand, as shown at the right in Figs. 6, 1 and 8. These tool holders are also made in various sizes so they may be used in various size lathes. I hese different size tool holders also accommodate high speed steel cutter bits of the most practical size for the work they are intended to do. It is advisable when obtaining a tool holder to specify the size lathe on

The illustrations on the opposite page show the most popular shapes of ground lathe tool cutter bits and their application. More complete information on grinding the cutter bits will be found on pages 5 to II.

In each of the following paragraphs one of the seven ground cutter bits shown is described, beginning with cutter bit “A,” Left Hand Turning Tool. A sample set of cutter bits already ground to shape may be purchased and used as patterns* if desired. This will be a big help to the beginner.

A—Left Hand Turning Tool—This tool is ground for machining work when fed from left to right, as indicated by Fig. I, Plate I, at left. The cutting edge is on the right side of the tool and the top of the tool slopes down away from the cutting edge. The right side and front of the tool are ground with sufficient clearance to permit the cutting edge to advance when the feed is engaged without the heel of the tool rubbing against the work.

B—Round Nosed Turning Tool —This tool is for general all around machine work and is used for taking light roughing cuts and finishing cuts. Usually, the top of the cutter bit is ground so that the tool may be fed from right to left although sometimes this cutter bit is ground flat on top so that the tool may be fed in either direction. (See Fig. 2, Plate I.)

C—Right Hand Turning Tool—This tool is just the opposite of Tool A and is designed to cut when fed from right to left. (See Fig. 3, Plate I.) The cutting edge is on the left side. This is an ideal tool for taking roughing cuts and for general all around machine work.

D—Left Hand Facing Tool—This tool is intended for facing on the left hand side of the work, as shown in Fig. 4, Plate I, page 2. The direction of feed should be away from the lathe center. The cutting edge is on the right hand side of the tool and the point of the tool is sharp to permit machining a square corner.

E—Threading Tool—The point of the threading tool is ground to a 60° included angle for machining United States or American National Form screw threads. (See Fig. 5, Plate I.) Usually, the top of the tool is ground flat and there is clearance on both sides of the tool so that it will cut on both sides.

F—Right Hand Facing Tool—This tool is just the opposite of Tool D. Left Hand Facing Tool, and is intended for facing the right end of the work and for machining the right side of a shoulder. (See Fig. 6, Plate I.)

G—Square Nosed Parting Tool—The principal cutting edge of this tool is on the front. (See Fig. 7, Plate 1.) Both sides of tool must have sufficient clearance to prevent binding and should be ground slightly narrower at the back than at the cutting edge. This tool is convenient for machining necks and grooves, squaring corners, etc. It may also be used for cutting off.

Equipment for Grinding and Sharpening Lathe Tool Cutter Bits

Good grinding equipment is essential for satisfactory grinding of lathe tool cutter bits. The illustration above shows an excellent type of grinder for this class of work. The grinder is motor driven and has two grinding wheels, one for rough grinding and the other for finish grinding the cutter bits. I he wheels arc 7 inches in diameter and have 3 4-inch face. A 36-grain vitrified wheel is used for rough grinding and a 60-grain wheel for finishing grinding.

The peripheral speed of the grinding wheel is approximately 5000 feet per minute. The grinding wheels are enclosed in close fitting guards, and the tool rest is convenient for some classes of grinding. The operator should wear goggles while grinding cutter bits if the grinder does not have glass spark shields.

The grinding wheels should be balanced so that they will run smoothly, and the wheel must be dressed frequently to keep it true. A Huntington type emery wheel dresser is usually used, although a fair job of wheel truing can be done with a broken piece of an old grinding wheel.

The water pot at the left of the grinder should be filled with water in which the

cutter bit may be cooled when it becomes heated from grinding.

Cutter bits may be mounted in a special holder (Fig. 9A) for grinding, if desired. This makes it easy to hold short lengths. Tool holders should not be used for grinding cutter bits because they may be accidentally damaged by the grinding wheel.

In addition to the grinder, a good oil stone is necessary. After grinding, the cutting edge of the cutter bit should always be honed with an oil stone, as shown in Fig. 10. Honing will not only improve the cutting quality of the cutter bit, but it will produce a better finish on the work and the cutting edge of the tool will stand up much longer than if it is not honed.

Fig. 10. Oil stone for honing dulling •dC« of cuttwr bit..

Grinding a Round Nosed Turning Tool for General Machine Work

The illustrations on this page. Figs. I I to 15. inclusive, show each step in the grinding of a round nosed turning tool for general machine work. 1 he various steps in grinding the cutter bit are as follows:

Fig. I I—Grind the left side of the cutter bit. holding the cutter bit at the correct angle against the wheel to form the side clearance, as shown in Fig. 20 on page 7. Use a coarse grinding wheel to remove most of the metal, and then finish on the side of the fine grinding wheel to produce a straight surface. (If ground on the periphery of a small diameter wheel the cutting edge will be undercut and will not have the correct angle.) Dip the cutter bit into water frequently while grinding to prevent overheating.

Fig. 12—Grind the right side of the cutter bit. holding at the required angle to form the right side. This angle is not important as it has very little to do with the cutting edge of the tool, except too much of the bit should not be removed, as the more metal left on the bit the better it absorbs the heat.

Fig. 13—Grind the radius or rounding on the end of the cutter bit. A small radius (approximately }£/') is preferable as a large radius may cause chatter. Hold the cutter bit lightly against the side of the wheel and turn from side to side to produce the desired radius. Be careful to hold the cutter bit at the correct angle to obtain the proper front clearance, as shown in Fig. 14 and also Fig. 21 on page 7.

Fig. 14 Hold the cutter bit at an angle as shown while grinding the radius on the end of the cutter bit in order to form the required front clearance. See Fig. 21 on page 7.

Fig. 15—Grind the top of the cutter bit, holding the cutter bit at the required angle to obtain the necessary side rake and back rake, as shown in Figs. 20 and 21 on page 7.

Hone the cutting edge all around and on top with an oil stone, as shown in Fig. 10, Page 4. until the cutting edge is very keen. The cutter bit will cut better and will last longer than if it is used without honing.

lie careful not to get the tool too hot dip tool in cold lOutcr occasionally to avoid hurnintf.

Correct Height oF the Cutting Edge

Straight Turning

The cutting edge of the cutter bit should be about 5° above center, or per inch in diameter of the work, as shown in Fig. 16 at right, for ordinary straight turning. The position of the cutter bit must be taken into consideration when grinding the various angles, as the height of the cutter bit determines the amount of front clearance necessary to permit free cutting.

For Cast Iron, Steel, etc.

Fig. 16. The cutting edge of the cutter bit should be 5° or per inch in diameter of the work above center for straight turning on cast iron, steel, etc.

Taper Turning, Thread Cutting, Brass Turning

The cutting edge of the cutter bit should always be placed exactly on center, as shown in Fig. 17. for all types of taper turning and boring, and for cutting screw threads, also for turning brass, copper and other tenacious metals.

Tool Angle Varies With Texture of Work

The included angle of the cutting edge of the cutter bit is known as the tool angle or angle of keenness and varies with the texture of the work to be machined. For example, when turning soft steel a rather acute angle should be used, but for machining hard steel or cast iron the cutting edge must be well supported and therefore the angle is less acute.

It has been found that an included angle of 61° is the most efficient tool angle for machining soft steel. This is the angle of the cutter bit as shown in

Fig. 18.

For machining ordinary cast iron, the included angle of the cutting edge should be approximately 71°, as shown in Fig. 19. However, for machining chilled iron or very hard grades of cast iron, the tool angle may be as great as 85°,

Fig. 18. The tool angle or included angle of cutting edge for machining soft steel should be approximately 61°.

For Cast Iron

Fig. 19. The tool angle or Included angle of the cutting cdKc f,,r machining ordinary rant iron should be approximately 71 .

For Brass, Copper, etc.

Fig. 17. The cutting edge of the cutter bit should be placed exactly on center for thread cutting, taper turning, machining brass, copper, etc.

Correct Angles for Grinding Cutter Bits

In order that the cutter bit may cut freely, it must be ground with side clearance, front clearance, side rake and back rake at the correct angles, as shown in Figs. 20 and 21.

Side Clearance—The side clearance should be from 3° to 10°, depending on the amount of feed used and the nature of the work, and is ground on the side of the cutter bit to permit the cutting edge to advance freely without the heel of the tool rubbing against the work. (See Fig. 20.)

Front Clearance—The front clearance should be from 3° to I 5°, depending on the nature of the work and height of the cutter bit, and is ground on the end of the cutter bit to permit the cutting edge to cut freely as it is fed to the work. (See

Fig. 21.)

Fig. 20. Correct side clearance and side rake of cutter bit.

Fig. 21. Correct front clearance and back rake of cutter bit.

Back Rake—The back rake is ground on the top of the cutter bit to facilitate free cutting. (See Fig. 21).

Side Rake—The side rake is ground on the top of the cutter bit to facilitate free cutting. (See Fig. 20.)

Tool Angl e—The tool angle or angle of keenness is the included angle of the cutting edge which is formed by the top and side of the cutter bit. (See Fig. 20).

Cutter Bit Grinding Gage

Fig. 22. Pattern for making cutter bit grinding gage.

A cutter bit grinding gage as shown in Fig. 22 at the left, is helpful for the beginner in grinding the correct angle on the various faces of the cutter bit. This gage can easily be made of sheet metal, using Fig.

22 as a pattern, which is full size.

Tool for Roughing Cuts

Figs. 26 and 27 illustrate an excellent tool for taking heavy roughing cuts to reduce the diameter of a steel shaft to the approximate size desired. This tool will cut freely but does not produce a very smooth finish. When using this type of tool it is advisable to leave sufficient stock for a finishing cut with the round nosed tool shown at the bottom of the page.

Grind the tool to the shape shown in Fig. 27 and use the cutter bit grinding gage shown in Fig. 22, page 7, for grinding the correct front clearance, side clearance, etc.

The cutting edge of the tool is straight and the point is only slightly rounded. A very small radius at the point (approximately \i\) will prevent the point of the tool from breaking down but will not impair the free cutting quality of the tool.

The tool angle or included angle of the cutting edge of this tool should be approximately 61° for ordinary machine steel. If a harder grade of alloy or tool steel is to be machined, the angle may be increased, and if free cutting Bessemer screw stock is to be machined, the angle may be slightly less than 61°.

Round Nosed Tool for Finishing Cuts

Figs. 28 and 29 illustrate a round nosed turning tool for taking finishing cuts. The tool is very much the same shape as the sharp pointed tool for rough turning shown above, except that the point of the tool is rounded. (Approximately to radius.)

This tool will produce a very smooth finish if. after grinding, the cutting edge is well honed with an oil stone and a fine automatic feed is used.

Fig. 31. Detail of round noned tool bit.

The round nosed turning tool shown above is ground flat on top so that the tool may be fed in either direction, as indicated by the arrows in Fig. 30. This is a very convenient tool for reducing the diameter of a shaft in the center. The shape of the cutter bit is shown in Fig. 31, and the correct angle for the front clearance and side clearance can be obtained by grinding to the gage shown in Fig. 22 on page 7.

Fig. 33. Detail of right hand turning tool.

The right hand turning tool shown above is the most common type of tool foi general all around machine work. This tool is used for machining work froit right to left, as indicated by the arrow in Fig. 32. The shape of the cutter bil is shown in Fig. 33. See page 7 for correct angles of clearance.

Left Hand Turning Tool

Fig. 34. Application of left hand turning tool.

End Vie*

Fig. 35. Detail of left hand turninv Ion

I he left hand turning tool illustrated in Figs. 34 and 35 is just the opposite c the right hand turning tool shown in Figs. M and 33. This tool is designed fci machining work from left to right.

Grinding Lathe Tool Cutter Bits

Right Hand Side Tool

58 Point

Top View

Side View End View

Fig. 37. Detail of right hand side tool.

The right hand side tool is intended for facing the ends of shafts and for machining work on the right side of a shoulder. This tool should be fed outward from the center, as indicated by the arrow in Fig. 36. The point of the tool is sharp and is ground to an angle of 58° to prevent interference with the tailstock center. When using this cutter bit care should be taken not to bump the end of

the tool against the lathe center, as this will break off the point. See page 7 for

correct angle of side clearance and front clearance.

Left Hand Side Tool

Fig. 38. Application of left hand side tool.

Side View End View

Fig. 39. Detail of left hand Ride tool.

The left hand side tool shown in Figs. 38 and 39 is just the reverse of the right hand side tool shown in Figs. 36 and 37. This tool is used for facing the left side of the work, as shown in Fig. 38.

Screw Thread Cutting Tool

Fig. 40. Application of screw thread cutting tool.

Side View End View

Fig. 41. Detail of thread cutting tool.

Figs. 40 and 41 show the standard type of cutter bit for cutting United States or American National Form screw threads. The cutter bit is usually ground flat on top. as shown in Fig. 40. and the point of the tool must be ground to an included angle of 60°, as shown in Fig. 41. Careful grinding and setting of this cutter bit will result in perfectly formed screw threads. When using this type of cutter bit to cut screw threads in steel, always keep the work flooded with lard oil in order to obtain a smooth thread. Machine oil may be used if no lard oil is available. Some operators do not use any oil. but for a smooth thread oil is essential. It is not necessarv to use oil when cutting screw threads in cast iron.

Grinding Lathe Tool Cutter Bits

Brass Turning Tool

Top View

The brass turning tool shown above is similar to the round nosed turning tool illustrated in Figs. 30 and 31 on page 9, except that the top of the tool is ground flat so that there is no side rake or back rake. This is to prevent the tool from digging into the work and chattering. The rounding on the end of the bit depends on the nature of the work being machined. A very small radius may be used on long slender work to reduce the tendency to chatter. However, a fairly large radius, as shown in the illustration, will produce a better finish.

Cutting Off Tool

Top View

Fig. 44. Application of cutting off tool.

The cutting off tool should always be set exactly on center, as shown in Fig. 44. This type of tool may be sharpened by grinding the end of the cutter blade to an angle of 5° as shown in Fig. 45. The sides of the blade have sufficient taper to provide side clearance, so do not need to be ground. When cutting off steel always keep the work flooded with oil. No oil is necessary when cutting olf cast iron.

Side View End View

Fig. 43. Detail of brass turning tool.

Boring and Inside Threading Tool

Fig. 47. Detail of boring tool. Fig. 48. lnitUlc threading tool,

The boring tool is ground exactly the same as the left hand turning tool shown in Figs. 34 and 35 on page 9, except the front clearance of boring tool must In-ground at a slightly greater angle so that the heel of the tool will not rub in the hole of the work. The inside threading tool is ground the same as the screw thread cutting tool, shown in Figs. 40 and 41 on page 10, except that the front clearance must be increased for the same reason as for the boring tool.

Grinding Stellite Cutter Bits

Stellite cutter bits are used for machining cast —

iron, malleable iron, steel, etc., when high cut- \ ting speeds are desirable. The recommended cutting speeds are shown in the table below.

Fig. 49. Stellite Cutter Bit.

Cutting Speeds in R.P.M. for Stellite Cutter Bits

Type Cast Iron Steel

Hurd Medium Malleable Caatinga SAE 3115 Cold Rolled

Rough 00- 1)0 100-150 125-175 HO-125 125-175 200-300

Finish 150-175 150-175 150-200 125-200 150-200 300-400

Stellite cutter bits are ground the same as high speed steel cutter bits, except that the clearance angle and the top rake are reduced to provide a better support for the cutting edge. Stellite is more brittle than high speed steel, so the cutting edge must be well supported to prevent chipping and breaking. I here should be just enough clearance to permit the tool to cut freely.

Grinding Tungsten Carbide Cutting Tools

Tungsten carbide tipped cutting tools are used for manufacturing operations where maximum cutting speeds are desired, and are highly efficient for machining cast iron, alloyed cast iron, copper, brass, bronze, aluminum, babbitt and abrasive non-metallic materials such as fibre, hard rubber and bakelite. Cutting speeds may vary from I 10 to 650 surface feet per minute. depending on the depth of cut and the feed.

Tungsten carbide tipped cutter bits must be ground on a special grade of grinding wheel, as they are so hard they cannot be satisfactorily ground on the ordinary grinding wheel. The cutting edge must be well supported to prevent chipping and should have just enough clearance to permit the tool to cut freely.

Detailed information on grinding and lapping tungsten carbide tools can be secured from the manufacturer from whom they are purchased.

Fig. 50. Tungsten Carbide Tipped Cutting Tool Mounted in Open Side Tool Post for Rigid Support.

Tantalum Carbide Cutting Tools

Tantalum carbide is a term applied to a combination of tungsten carbide and tantalum carbide. Tantalum carbide tipped cutting tools are similar to tungsten carbide tools, but are used mostly for machining steel.

Titanium Carbide Cutting Tools

Titanium carbide is a term applied to a combination of tungsten carbide and titanium carbide. Titanium carbide is interchangeable with tantalum carbide in its* uses.

Fig. SI. Machining u Steel Shaft at High Speed with Tantalum Carbide Tipped Cutting Tool.

“How to Cut Screw Threads in the Lathe”

BULLETIN NO. 36-A Shows How to Set Up the Lathe, Adjust the Tool, Etc.

Detailed information explaining just how to cut screw threads in the back-geared, screw cutting lathe will be found in this booklet.

Information given includes: how to set up the lathe for cutting various pitches of screw threads; how to set the cutter bit; standard screw thread formulas; information on cutting left hand threads, multiple threads, metric threads, etc.

The book provides a handy reference for the amateur machinist on screw thread cutting. Contains 24 pages, size 6" x 9" and over 50 illustrations.

Price 10c postpaid. U. S. stamps accepted for single copies. Contain* 2-1 pages, size 6" x 9'.

“How to Run a Lathe

A Complete Reference Book On Lathe Care and Operation

“Mow to Run a Lathe” is a complete reference book and manual on the care and operation of the back-geared screw-cutting lathe. 11 is a practical handbook for the machinist, lathe operator, apprentice. or shop student. Clearly written in simple, non-technical language, the instruction material is easy for the beginner to understand.

This book has been improved and perfected by suggestions, criticisms, and ideas that have been submitted by hundreds of practical shop men. I he latest shop practices and methods used in modern industry are accurately described.

PARTIAL LIST OF CONTENTS

History of the Lathe

Erecting nnd Leveling the Lathe

Operation of Lathe Controls

Lathe Tools nnd Their Application

How to Take Accurate Measurements

Muchining Work Between Centers Chuck Work Taper Turning and Boring

Drilling, Reaming and Tapping Cutting Screw Thread* Special Classes of

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