Tips and tricks
Lathe and planer tools
LATHE AND PLANER TOOLS
CONTENTS
- Cutting Tools for Planer and Lathe
- Boring Tools
- Forging Lathe Boring Tools
- Shape of Standard Shop Tools
- Cutting Speeds and Feeds for Lathe Tools
- Straight and Circular Forming Tools
Machinery's reference series
1912, The Industrial Press, New York
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Lathe and planer tools
CHAPTER I
CUTTING TOOLS FOR PLANER AND LATHE
In discussing cutting tools for the planer and lathe, planer tools will first come under our notice as being the simplest and requiring the least skill in setting. Every mechanic has doubtless observed that if the chip be unwound from the spiral shape it assumes in leaving the tool, and projected in a straight line, it is shorter than the surface from which it came. This is due mainly to the compression of the metal in the direction of the cut, and the possibilities of saving power and strain upon the machine by giving proper cutting angles to the tools and reducing this compression to a minimum is thus realized.
Bake of Planer Tools
In Fig. 1 the cutting tool is at right angles to the work and without rake. It exerts its force in a direction nearly parallel to the surface of the work, and having no side rake either, it simply does not cut, but shoves or crowds the metal forward, producing a chip made up of little splints. It cannot exert any force tending to lift or curl the chip. The tool is wholly wrong; nor would it materially improve it to grind it like the tool shown in the little sketch at the right, which goes to the other extreme, and would spring into the work. A tool must first of all be heavy enough at the back or heel to resist the horizontal cutting force, and consequently should have very little clearance. The 7 degrees clearance shown in the lathe tool in the upper view, Fig. 2, is too much for a planer tool, while the 3 degrees of the lower sketch is as small as can be used safely. Theoretically if the point leads by only a thousandth or two it will perform its function. There should be very little top rake on account of its tendency to make the tool dig into the cut; but this can be compensated for by giving considerable side rake.
Another reason why a planer tool tends to dig into the work is illustrated in Fig. 3. Point A in the sketch is the fulcrum. In the first sketch the tendency is for the tool to dig into the work in the direction of the arrow. This is not so serious as appears on the face of it, as planer tools are usually so stiff that they will spring but little, and any error that might occur in the roughing cut would be eliminated in the finishing cut. What many mechanics take as an indication of the spring of the tool is really due to the chatter of the planer, since a rack and pinion planer will frequently chatter after it has become worn, while in a worm-driven planer the lost motion is all taken up at one end before beginning the cut, and the screw action does away with the chatter. To obviate any spring into the work, the tool may be designed as in the second sketch, Fig. 3, where the deflection due to the force of cut is away from the work.
The tool in Fig. 4 approaches the ideal for a finishing tool, and gives the best finished surface of any used on planer or shaper. It is made from a piece of ordinary tool steel and forged on the end to the shape indicated. It will be noticed that it has side rake, and instead of being straight on the bottom, the line that comes in contact with the work is a little rounding.
The Cutting Edges of Lathe Tools
We will now take up the subject of the cutting edges of some of the many varieties of lathe tools, Fig. 5. Here are shown diamond point, round-nose, side, centering, thread-cutting and cutting-off tools. We will first of all consider the diamond point tool, as it is by far more of a universal tool than any of the others. Before speaking of rake, clearance, or the setting of the tool, attention should be called to the general form of the cutting edges and the importance of maintaining the same throughout the life of the tool. Fig. 7 will best illustrate this. The tool as shown at the left, with depth of cut, is ground so that angle x shall not be less than 55 degrees. To the right is a tool in which the angle has been changed by grinding on both sides of the point, only because the machinist claims that he is in a hurry and must make time on his work. But it will be seen that the length of cut is much greater than the line of resistance a, showing loss in efficiency in the tool, and requiring more power to drive it after it had been ground. Nor is this the only reason why careless grinding will produce a loss. This is true with proper rake, angles and clearance, but when the mechanic ignores all principles and is careless, besides, how much more serious it becomes, because more finishing cuts will be required to make the piece straight. The nearer the cutting edge of the tool comes to being parallel with the axis of the work, the more power will be required to operate the tool.
It will be interesting to note what really takes place in turning, as shown in diagrammatic form in Fig. 8. Here is represented a piece of rough stock that is to be turned as indicated at the right. First, starting at the center line A, and developing the line of circumference in a straight path, we will get a line like (1). After turning and repeating the process, the developed line will look like the line at (2). It will be noted that the second line is somewhat irregular, showing that even after roughing off, the surface of the piece has nearly all the irregularities of the rough stock, though on a smaller scale. This brings us to another important point, and that is the necessity of centering work as accurately as possible, for no matter how even the work may be on its circumference, if centered out of true, it will not be round after turning, because the thickness of the chip or shaving is not uniform, hence does not offer uniform resistance to the cutting edge, and the work will bend more at one point than at another. If the cut were uniform and offered the same resistance, of course we could expect round work.
The bottom figure in Fig. 8 illustrates the tool for, and method of, obtaining the lines. A long light lever has a knife edge or point at one end, near the fulcrum, which bears against the periphery of the work. On the other end is a lead pencil attachment, the point bearing against the piece of paper indicated, the paper traveling at the same rate of speed as the work, only in the direction of the axis of the work. Any unevenness in the surface of the work raises or lowers the point of the pencil, and as the ratio is great (20 to 1), the variation in the line is marked.
Speeds and Feeds
Following is a table of finishing speeds and feeds for different metals for tools of ordinary tool steel. In roughing, the axiom is slow speed and quick feed; in finishing, high speed and fine feed. From this table 25 per cent should be deducted for roughing speed, making 18, 24, 28 and 83. Experiments on cutting tools made in the shops of H. H. Smith, London, England, and verified by the author, show that machine steel requires from two to two and one-half times the power for cutting as does cast iron, and wrought iron about one and one-half times the power. The results are given in detail in the chart, Fig. 17, which shows the increased force required for increased feed and depth of cut.
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Lathe and planer tools
Bake of Planer Tools
In Fig. 1 the cutting tool is at right angles to the work and without rake. It exerts its force in a direction nearly parallel to the surface of the work, and having no side rake either, it simply does not cut, but shoves or crowds the metal forward, producing a chip made up of little splints. It cannot exert any force tending to lift or curl the chip. The tool is wholly wrong; nor would it materially improve it to grind it like the tool shown in the little sketch at the right, which goes to the other extreme, and would spring into the work. A tool must first of all be heavy enough at the back or heel to resist the horizontal cutting force, and consequently should have very little clearance. The 7 degrees clearance shown in the lathe tool in the upper view, Fig. 2, is too much for a planer tool, while the 3 degrees of the lower sketch is as small as can be used safely. Theoretically if the point leads by only a thousandth or two it will perform its function. There should be very little top rake on account of its tendency to make the tool dig into the cut; but this can be compensated for by giving considerable side rake.
Another reason why a planer tool tends to dig into the work is illustrated in Fig. 3. Point A in the sketch is the fulcrum. In the first sketch the tendency is for the tool to dig into the work in the direction of the arrow. This is not so serious as appears on the face of it, as planer tools are usually so stiff that they will spring but little, and any error that might occur in the roughing cut would be eliminated in the finishing cut. What many mechanics take as an indication of the spring of the tool is really due to the chatter of the planer, since a rack and pinion planer will frequently chatter after it has become worn, while in a worm-driven planer the lost motion is all taken up at one end before beginning the cut, and the screw action does away with the chatter. To obviate any spring into the work, the tool may be designed as in the second sketch, Fig. 3, where the deflection due to the force of cut is away from the work.
The tool in Fig. 4 approaches the ideal for a finishing tool, and gives the best finished surface of any used on planer or shaper. It is made from a piece of ordinary tool steel and forged on the end to the shape indicated. It will be noticed that it has side rake, and instead of being straight on the bottom, the line that comes in contact with the work is a little rounding.
The Cutting Edges of Lathe Tools
We will now take up the subject of the cutting edges of some of the many varieties of lathe tools, Fig. 5. Here are shown diamond point, round-nose, side, centering, thread-cutting and cutting-off tools. We will first of all consider the diamond point tool, as it is by far more of a universal tool than any of the others. Before speaking of rake, clearance, or the setting of the tool, attention should be called to the general form of the cutting edges and the importance of maintaining the same throughout the life of the tool. Fig. 7 will best illustrate this. The tool as shown at the left, with depth of cut, is ground so that angle x shall not be less than 55 degrees. To the right is a tool in which the angle has been changed by grinding on both sides of the point, only because the machinist claims that he is in a hurry and must make time on his work. But it will be seen that the length of cut is much greater than the line of resistance a, showing loss in efficiency in the tool, and requiring more power to drive it after it had been ground. Nor is this the only reason why careless grinding will produce a loss. This is true with proper rake, angles and clearance, but when the mechanic ignores all principles and is careless, besides, how much more serious it becomes, because more finishing cuts will be required to make the piece straight. The nearer the cutting edge of the tool comes to being parallel with the axis of the work, the more power will be required to operate the tool.
It will be interesting to note what really takes place in turning, as shown in diagrammatic form in Fig. 8. Here is represented a piece of rough stock that is to be turned as indicated at the right. First, starting at the center line A, and developing the line of circumference in a straight path, we will get a line like (1). After turning and repeating the process, the developed line will look like the line at (2). It will be noted that the second line is somewhat irregular, showing that even after roughing off, the surface of the piece has nearly all the irregularities of the rough stock, though on a smaller scale. This brings us to another important point, and that is the necessity of centering work as accurately as possible, for no matter how even the work may be on its circumference, if centered out of true, it will not be round after turning, because the thickness of the chip or shaving is not uniform, hence does not offer uniform resistance to the cutting edge, and the work will bend more at one point than at another. If the cut were uniform and offered the same resistance, of course we could expect round work.
The bottom figure in Fig. 8 illustrates the tool for, and method of, obtaining the lines. A long light lever has a knife edge or point at one end, near the fulcrum, which bears against the periphery of the work. On the other end is a lead pencil attachment, the point bearing against the piece of paper indicated, the paper traveling at the same rate of speed as the work, only in the direction of the axis of the work. Any unevenness in the surface of the work raises or lowers the point of the pencil, and as the ratio is great (20 to 1), the variation in the line is marked.
Speeds and Feeds
Following is a table of finishing speeds and feeds for different metals for tools of ordinary tool steel. In roughing, the axiom is slow speed and quick feed; in finishing, high speed and fine feed. From this table 25 per cent should be deducted for roughing speed, making 18, 24, 28 and 83. Experiments on cutting tools made in the shops of H. H. Smith, London, England, and verified by the author, show that machine steel requires from two to two and one-half times the power for cutting as does cast iron, and wrought iron about one and one-half times the power. The results are given in detail in the chart, Fig. 17, which shows the increased force required for increased feed and depth of cut.
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Lathe and planer tools
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