thumb|thumb|300px|right|Various tool bits, carbide inserts and holders
thumb|thumb|300px|right|Typical hand ground cutting tool angles for the lathe.

The term '''tool bit''' generally refers to a non-rotary cutting tool used in metal lathes, planers. Such cutters are also often referred to by the set-phrase name of '''single-point cutting tool'''. The cutting edge is ground to suit a particular machining operation and may be resharpened or reshaped as needed. The ground tool bit is held rigidly by a tool holder while it is cutting.

==Geometry==
Back Rake is to help control the direction of the chip, which naturally curves into the work due to the difference in length from the outer and inner parts of the cut. It also helps counteract the pressure against the tool from the work by pulling the tool into the work.

Side Rake along with back rake controls the chip flow and partly counteracts the resistance of the work to the movement of the cutter and can be optimized to suit the particular material being cut. Brass for example requires a back and side rake of 0 degrees while aluminum uses a back rake of 35 degrees and a side rake of 15 degrees.

Nose Radius makes the finish of the cut smoother as it can overlap the previous cut and eliminate the peaks and valleys that a pointed tool produces. Having a radius also strengthens the tip, a sharp point being quite fragile.

All the other angles are for clearance in order that no part of the tool besides the actual cutting edge can touch the work. The front clearance angle is usually 8 degrees while the side clearance angle is 10-15 degrees and partly depends on the rate of feed expected.

Minimum angles which do the job required are advisable because the tool gets weaker as the edge gets keener due to the lessening support behind the edge and the reduced ability to absorb heat generated by cutting.
 
The Rake angles on the top of the tool need not be precise in order to cut but to cut efficiently there will be an optimum angle for back and side rake.

==Materials==
===Steels===
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===

Carbide, ceramics (such as cubic boron nitride), and diamond, having higher hardness than HSS, all allow faster material removal than HSS in most cases.  Because these materials are expensive and difficult to work with, typically the body of the cutting tool is made of steel, and a small cutting edge made of the harder material is attached.  The cutting edge is usually either screwed on (in this case it is called an insert), or brazed on to a steel shank (this is usually only done for carbide).

==Inserts==

Almost all high-performance cutting tools use indexable inserts. There are several reasons for this.  First of all, at the very high cutting speeds and feeds supported by these materials, the cutting tip can reach temperatures high enough to melt the brazing material holding it to the shank.  Economics are also important; inserts are made symmetrically so that when the first cutting edge is dull they can be rotated, presenting a fresh cutting edge.  Some inserts are even made so that they can be flipped over, giving as many as 16 cutting edges per insert. There are many types of inserts: some for roughing, some for finishing.  Others are made for specialized jobs like cutting threads or grooves. The industry employs standardized nomenclature to describe inserts by shape, material, coating material, and size.

==Form tools==

thumb|thumb|300px|right|This form tool is for a shift knob on a motorcycle. O-rings went into the grooves after machining from 6061-T6 Aluminum. This tool has an 8-degree rake from top to bottom for clearance. This tool was designed for a 2G [[Brown & Sharpe screw machine.]]

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 box tools. 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 took more work to make the part. For example, a form tool can turn many diameters and in addition can also cut off the part in a single operation and eliminate the need to index the turret. For single-spindle machines, bypassing the need to index the turret can dramatically increase hourly part production rates.

On long-running jobs it is common to use a ''roughing tool'' on a different slide or turret station to remove the bulk of the material, then finish with a finishing form tool. This increases the lifespan of the finishing tool's finely ground edge and ensures that the 5,000th part receives the same nice finish and dimensional precision that the first part received.

'''バイト'''（オランダ語beitel, 英語tool bit）とは、ISOで基本的な大きさが取り決められている。

<!-- 明治時代初期には、当時の先進国であったオランダから多くの工業製品が輸入されている -->

; ノーズ (Nose)
: ノーズとはバイトの刃の先端部分を指す。ピンと尖っていると容易に刃こぼれしてしまうため、多かれ少なかれ意図的に丸みを付けて予防している。
; チップブレーカ (Chip Breaker)
: チップブレーカとは、バイトのスクイ面に取り付け、あるいは研ぎ込まれるもので、切削時に排出される切屑(チップ)を均一に巻いたり、あるいは破断させ、切削し易くする。インサートの場合は、一般にプレス成形により製造されプレス用金型の表面形状が転写されるため、チップブレーカとして作用する形状をこの工程で作り込んでしまうことが多い。
; シャンク (Shank)
: シャンクとは、バイトを刃物台に保持するための部分（刃以外の部分）を示す。またシャンクには12×12、16×16等その角のサイズがあり、その数値から12mm角バイト、16mm角バイト等と呼ばれる。

切削加工の際バイトには大きな負荷がかかっており、剛性が不足する状況ではビビリが生じる場合がある。ビビリを積極的に利用する特殊なバイトも中にはあるが、一般的には加工に応じた適切なサイズのバイトを使用したり加工条件を変更するなどして未然に防ぐことが重要である。