Lathe Tools

Lathe Tools

Introduction

Depending on the type of work that is being performed, each machinist develops a collection of tools that may be used frequently.

Certain types of tools perform much better than other types, yet unique circumstances may present a limited number of tooling options. If a carbide insert tooling is not available, a successful lathe machinist will be able to grindhis own tooling, be it high speed steel or brazed carbide tool bits

High Speed Steel

Figure 1

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Prior to World War II the most common type of lathe bit was made from high speed tool steel. High speed tooling is a steel alloy with a predetermined percentage of tungstenmixed in. There is also a hardeningprocess that makes high speed tooling wear resistant. These tools are able to withstand high work temperatures. Tools typically made from high speed are end mills (figure 1), drills (figure 2)and reamers (figure 3), and lathe tool bits (figure 4)

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Figure 4

   

 

Knurling Tool

The knurling tool is not a cutting tool, but a tool that leaves a diamond impression in the work. It accomplishes this because there are either two or three tool steel quality "rollers" in a knurling tool. The tool steel means that the rollers are harder than the parts being machined. When the rollers engage the part and a very slow feed and RPMare used, the knurling tool produces a knurled finish on the part. This finish is actually pressed by the rollers of the knurling tool, and this pressure forms a diamond pattern. There should be care taken that all work is properly supported while knurling, as the extreme pressure will cause damage if the part should come loose. It is also possible to shatter the rollers of the knurling tool, and these flying objects could cause eye damage

Carbides

Carbides are made by blending micron-sized tungsten carbide and cobalt powders, then pressing the mixture in a mold and at a temperature high enough to cause the cobalt to flow. During this process the cobalt fills the spaces between the tungsten grains and thoroughly coats each grain. When the cobalt solidifies, it cements the grains together, forming a dense composite. This process is called "sintering" and the resulting tool is called "cemented" carbide.


Cemented carbides get their hardness from the tungsten grains and their toughness from the tight bonds produced by the cementing action of the cobalt metal*. By varying the amount of cobalt the hardness, wear resistance and toughness (shock resistance) of the carbide can be changed.
The beginning of tungsten carbide production may be traced to the early 1920's, when the German electrical bulb company, Osram, looked for alternatives to the expensive diamond drawing dies used in the production of tungsten wire.
These attempts led to the invention of cemented carbide, which was soon produced and marketed by several companies for various applications where its high wear resistance was particularly important. The first tungsten carbide cobalt grades were soon successfully applied in the cutting and milling of cast iron. In the early 1930's, the pioneering cemented carbide companies launched the first steel-milling grades which, in addition to tungsten carbide and cobalt, also contained carbides oftitanium and tantalum

Tool Posts

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Figure 2

The type of tool post shown in figure1 is used more for heavy duty work. It allows for various different tools to be used without changing the tool holding mechanism of the lathe. Each tool is bolted into the tool post by means of three or four bolts, and if needed, shim stock can be used under the tool bit to achieve proper center height.

Figure 3

Note that quick change tool posts (figure 2) are available with many tool holder options (figure 3) and arre easy to use (see video at that bottom of the page).
The standard tool post (figure 4) is used in conjunction with high speed steel tooling. This type of tool post can only be used where cutting forces are kept low because they have a tendency to move around under heavy cutting pressure. The standard tool post uses a tool post clamp screw to hold the tool holder down onto the rocker. The rocker is used to adjust the tool height to the center of the spindle.

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