tool

Materials

Originally, all tool bits were made of high carbon tool steels with the appropriate hardening and tempering. Since the introductions of high-speed steel (HSS) (early years of the 20th century), sintered carbide (1930s), and ceramic cutters, those materials have gradually replaced the earlier kinds of tool steel in almost all cutting applications. Most tool bits today are either HSS or carbide.

Carbides and ceramics

By confining the expensive hard cutting tip to the part doing the actual cutting, the cost of tooling is reduced. The supporting tool holder can then be made from a tougher steel, which besides being cheaper is also usually better suited to the task, being less brittle than the cutting-edge materials.

The tool holders may also be designed to introduce additional properties to the cutting action, such as

• Angular approach - direction of tool travel.
• Spring loading - deflection of the tool bit away from the material when excessive load is applied.
• Variable overhang - the tool bit may be extended or retracted as the job requires.
• Rigidity - the tool holder can be sized according to the work to be performed.
• Direct cutting fluid or coolant to the work area.

Note that since stiffness (rather than strength) is usually the design driver of a tool holder, the steel used doesn't need to be particularly hard or strong as there is relatively little difference between the stiffnesses of most steel alloys.

A form tool is precision-ground into a pattern that resembles the part to be formed. The form tool can be used as a single operation and therefore eliminate many other operations from the slides (front, rear and/or vertical) and the turret, such as boxtools. A form tool turns one or more diameters while feeding into the work. Before the use of form tools, diameters were turned by multiple slide and turret operations, and thus more work to make the part. For example, a form tool can turn many diameters and in addition can also cutoff the part in a single operation and eliminate indexing the turret.

For single-spindle machines, bypassing indexing the machine can dramatically increase hourly part production. On long-running jobs it is common to use a ‘roughing tool’ tool on a different slide, or from the turret to remove the bulk of material to reduce wear on the form tool. There are also different types of form tools. Insert tools are the most common for short- to medium-range jobs (50 to 20,000 pcs). Circular form tools are usually for longer jobs, since the tool wear can be ground off the tool tip many times as the tool is rotated in its holder. There is also a skiving tool that can be used for light finishing cuts. Form tools can be made of cobalt, carbide, or high-speed steel. Carbide requires additional care because it is very brittle and will chip if chatter occurs.

A drawback when using form tools is that the feed into the work is usually slow, .0005" to .0012" per revolution depending on the width of the tool. Wide form tools create more heat and usually are problematic for chatter. Heat and chatter reduces tool life. Also, form tools wider than 2.5 times the smaller diameter of the part being turned have a greater risk of the part breaking off. When turning longer lengths, a support from the turret can be used to increase turning length from 2.5 times to 5 times the smallest diameter of the part being turned, and this also can help reduce chatter. Despite the drawbacks, the elimination of extra operations often makes using form tools the most efficient option.

Many tools or groups of tools serve to perform one or more of a set of basic operations, such as:

• Cutting (knife, scythe, sickle, etc...)
• Concentrating force (hammer, maul, screwdriver, whip, writing implements, etc...)
• Guiding (set square, straightedge, etc...)
• Protecting
• Seizing and holding (pliers, glove, wrench, etc...)

Tool substitution

Often, by design or coincidence, a tool may share key functional attributes with one or more other tools. In this case, some tools can substitute for other tools, either as a make-shift solution or as a matter of practical efficiency. "One tool does it all" is a motto of some importance for workers who cannot practically carry every specialized tool to the location of every work task. Tool substitution may be divided brols are not widely known. As an example of the former, many wood-cutting hand saws integrate a carpenter's square by incorporating a specially shaped handle which allows 90° and 45° angles to be marked by aligning the appropriate part of the handle with an edge and scribing along the back edge of the saw. The latter is illustrated by the saying "All tools can be used as hammers." Nearly all tools can be repurposed to function as a hammer, even though very few tools are intentionally designed for it.