This section is from the book "Lathe Design, Construction And Operation, With Practical Examples Of The Lathe Work", by Oscar E. Perrigo. Also available from Amazon: Lathe Design: Construction And Operation.
Lathe tools in general. A set of regular tools. Tool angles. Materials and their characteristics. Their relation to the proper form of tools. Behavior of metals when being machined. The four requisites for a tool. The strength of the tool. The form of the tool. Degree of angles. Roughing and finishing tools. Spring tools. Tool-holders. Grinding tools for tool-holders. Dimensions of tools for tool-holders. The Armstrong tool-holders. Economy of the use of tool-holders. High-speed steel. A practical machinist's views on high-speed steel tools. Conditions of its use. Preparing the tool. Testing the tool. Speeds and feeds. Much difference of opinion. Grinding the tools. Amount of work accomplished by high-speed steel tools. Average speed for lathes of different swing. Speeds of high-speed steel drills. Mr. Walter Brown's observations on high-speed steel. Its brittleness. Its treatment. The secret of its successful treatment. Method of hardening and tempering. Method of packing. Making successful taps. Speeds for the use of high-speed steel tools. Economy in the use of highspeed steel tools. Old speeds for carbon steel tools. Modern speeds. Relative speeds and feeds. Modern feeds for different materials. Lubrication of tools. The kind of lubricant. Applying the lubricant. Lubricating oils. Soapy mixtures. Formula for lubricating compound. Improper lubricants. Various methods of applying lubrir-cants. The gravity feed. Tank for lubricant. Pump for lubricant. Power for driving machine tools. Calculating the power of a driving-belt. Impracticability of constructing power tables. Collecting data relating to these subjects. Flather's "Dynamometers and the Transmission of Power." Pressure on the tool. Method of calculating it. Flather's formula. Manchester Technology data. Pressure on tools.
With comparatively slight exceptions the ordinary lathe tools are of the same form as those used in the time of the old chain lathe with a wooden bed. While the modern machinist has found some new shapes for special work and has been provided with all sorts and forms of tool-holders, and it is probable that many new and perhaps improved forms will be brought out in the future, the same old forms will probably be used for a considerable part of lathe work as long as there is a lathe to use them on.
Fig. 187. - A Set of Ordinary Lathe Tools.
A set of fourteen of these time-honored tools is shown in Fig. 187, which are usually known by the following names, the numbers given in the engraving being referred to:
1. Right-hand Side Tool.
2. Left-hand Side Tool.
3. Right Bent Side Tool.
4. Right-hand Diamond Point.
5. Left-hand Diamond Point.
6. Round Nose Tool.
7. Cutting-down Tool.
8. Cutting-off Tool.
9. Narrow Round Nose Tool.
10. Wide Round Nose Tool.
11. Inside Boring Tool.
12. Straight Thread Tool.
13. Bent Thread Tool.
14. Inside Thread Tool.
In nearly all these tools their names indicate their uses, which is quite apparent also from their form.
The question of the proper angles to which lathe tools should be formed is an important one and there are a good many theories in relation to the subject. It is a matter of continual discussion among shop-men who are inclined to disagree very much on the subject. It is altogether probable that this disagreement is not so much that the question is one impossible of solution as it is that each man determines the question for himself from the standpoint of his own experience and with the range of material with which he has to work: otherwise, with the conditions which govern the work under his observation.
These conditions are so varied and so numerous that no fixed rules for forming tools to meet them all is possible. Some of them are these:
We have ordinarily to handle such materials as tool steel, machine steel, steel castings, wrought iron, cast iron, bronze, brass, copper, aluminum, babbitt metal, hard rubber, vulcanized fiber, rawhide, and a number of others constantly coming to hand. These substances as here mentioned give a very wide range to the kind and shape of the tools that it will be proper to use. But there are varying degrees and conditions in the same material that still further complicate the question.
Steel may be hard and brittle, or it may be soft and tough. It may be of any percentage of carbon up to and perhaps over one hundred points, and still we must make a tool to cut it.
Wrought iron may have somewhat similar properties as steel, but, of course, in a much less degree.
The alloys of copper commonly known as hard bronze, nickel bronze, gun metal, brass, yellow brass, and so on, through an almost endless variety of mixtures, will require almost as many different forms as must be used in turning the different grades of steel.
And so it is to a greater or less extent with all the different materials with which we have to deal.
In a general way we may say that the quality of the material we have to cut will influence the results in two ways: first, as to whether it is hard or soft, and second, whether it is crystalline or fibrous. Its varying degrees of hardness or softness determine whether much or little can be removed in a given time; or, what amounts to the same thing, whether the speed of the cutting shall be fast or slow, and whether the feed shall be coarse or fine. Its crystalline or its fibrous nature will make considerable difference in the top angles of the tools, and this will be readily seen in the tendency of the crystalline metal to break up into small chips, while the fibrous turnings will curl off into spiral or helical shavings. Therefore the fibrous material will have the sharper angle than that designed for the crystalline structure of metal.