Machine taper

A machine taper is a system for securing cutting tools, workholders or toolholders in the spindle of a machine tool or power tool. A male member of conical form fits into the female socket, which has a matching taper of equal angle.
Almost all machine tool spindles, and many power tool spindles, have a taper as their primary method of attachment for tools. Even on many drill presses, handheld drills, and lathes, which have chucks, the chuck is attached by a taper. On drills, drill presses, and milling machines, the male member is the tool shank or toolholder shank, and the female socket is integral with the spindle. On lathes, the male may belong to the tool or to the spindle; spindle noses may have male tapers, female tapers, or both.

Explanation

operators must be able to install or remove tool bits quickly and easily. A lathe, for example, has a rotating spindle in its headstock, to which one may want to mount a spur drive or work in a collet. Another example is a drill press, to which an operator may want to mount a bit directly, or using a drill chuck.
Virtually all milling machines, from the oldest manual machines up to the most modern CNC machines, use tooling that is piloted on a tapered surface.
The machine taper is a simple, low-cost, highly repeatable, and versatile tool mounting system. It provides indexability, as tools can be quickly changed but are precisely located both concentrically and axially by the taper. It also allows high power transmission across the interface, which is needed for milling.
Machine tapers can be grouped into self-holding and self-releasing classes. With self-holding tapers, the male and female wedge together and bind to each other to the extent that the forces of drilling can be resisted without a drawbar, and the tool will stay in the spindle when idle. It is driven out with a wedge when a tool change is needed. [|Morse] and [|Jacobs] tapers are an example of the self-holding variety. With self-releasing tapers, the male will not stick in the female without a drawbar holding it there. However, with good drawbar force, it is very solidly immobile. [|NMTB/CAT], BT and [|HSK] are examples of the self-releasing variety.For light loads, tools with self-holding tapers are simply slipped onto or into the spindle; the pressure of the spindle against the workpiece drives the tapered shank tightly into the tapered hole. The friction across the entire surface area of the interface provides a large amount of torque transmission, so that drawbars, splines or keys are not required.
For use with heavy loads, there is usually a key to prevent rotation and/or a threaded section, which is engaged by a drawbar that engages either the threads or the head of a pull stud that is screwed into them. The drawbar is then tightened, drawing the shank firmly into the spindle. The draw-bar is important on milling machines as the transverse force component would otherwise cause the tool to wobble out of the taper.
All machine tapers are sensitive to chips, nicks, and dirt. They will not locate accurately, and the self-holding variety will not hold reliably, if such problems interfere with the seating of the male into the female with firm contact over the whole conical surface. Machinists are trained on keeping tapers clean and handling them in ways that prevent them from being nicked by other tools. CNC tool-changing cycles usually include a compressed-air blast while one toolholder is being swapped with the next. The air blast tends to blow away chips that might otherwise end up interfering between the toolholder and spindle.

Use

Tools with a tapered shank are inserted into a matching tapered socket and pushed or twisted into place. They are then retained by friction. In some cases, the friction fit needs to be made stronger, as with the use of a drawbar, essentially a long bolt that holds the tool into the socket with more force than is possible by other means.
Caution needs to be exercised in the usual drilling machine or lathe situation, which provides no drawbar to pull the taper into engagement, if a tool is used requiring a high torque but providing little axial resistance. An example would be the use of a large diameter drill to slightly enlarge an existing hole. In this situation, there may be considerable rotary loading. In contrast, the cutting action will require very little thrust or feed force. Thrust helps to keep the taper seated and provides essential frictional coupling.
The tang is not engineered to withstand twisting forces which are sufficient to cause the taper to slip, and will frequently break off in this situation. This will allow the tool to spin in the female taper, which is likely to damage it. Morse taper reamers are available to alleviate minor damage.
Tapered shanks "stick" in a socket best when both the shank and the socket are clean. Shanks can be wiped clean, but sockets, being deep and inaccessible, are best cleaned with a specialized taper cleaning tool which is inserted, twisted, and removed.
Tapered shank tools are removed from a socket using different approaches, depending on the design of the socket. In drill presses and similar tools, the tool is removed by inserting a wedge shaped block of metal called a "drift" into a rectangular shaped cross hole through the socket and tapping it. As the cross section of the drift gets larger when the drift is driven further in, the result is that the drift, bearing against the foremost edge of the tang, pushes the tool out. In many lathe tailstocks, the tool is removed by fully withdrawing the quill into the tailstock, which brings the tool up against the end of the leadscrew or an internal stud, separating the taper and releasing the tool. Where the tool is retained by a drawbar, as in some mill spindles, the drawbar is partially unthreaded with a wrench and then tapped with a hammer, which separates the taper, at which point the tool can be further unthreaded and removed. Some mill spindles have a captive drawbar which ejects the tool when actively unscrewed past the loose stage; these do not require tapping. For simple sockets with open access to the back end, a drift punch is inserted axially from behind and the tool tapped out.

Types

There are many standard tapers, which differ based on the following:

the diameter at the small end of the truncated cone
the diameter at the large end of the truncated cone and
the axial distance between the two ends of the truncated cone.

The standards are grouped into families that may include different sizes. The taper within a family may or may not be consistent. The Jarno and NMTB tapers are consistent, but the Jacobs and Morse families vary.
There are adaptors available to allow the use of one type of taper tooling, e.g. Morse, on a machine with a different taper, e.g. R8 or vice versa, and simpler adaptors consisting of an externally and internally tapered sleeve to allow a small Morse tool to be used in a machine of larger bore.
One of the first uses of tapers was to mount drill bits directly to machine tools, such as in the tailstock of a lathe, although later drill chucks were developed that held parallel shank drill bits.

Brown & Sharpe

tapers, standardized by the company of the same name, are an alternative to the more-commonly seen Morse taper. Like the Morse, these have a series of sizes, from 1 to 18, with 7, 9 and 11 being the most common. Actual taper on these lies within a narrow range close to.500 inches per foot.

Size	Lg. Dia.	Sm. Dia.	Length	Taper	Taper
1	0.2392	0.2000	0.94	0.5020	0.04183
2	0.2997	0.2500	1.19	0.5020	0.04183
3	0.3753	0.3125	1.50	0.5020	0.04183
4	0.4207	0.3500	1.69	0.5024	0.04187
5	0.5388	0.4500	2.13	0.5016	0.04180
6	0.5996	0.5000	2.38	0.5033	0.04194
7	0.7201	0.6000	2.88	0.5010	0.04175
8	0.8987	0.7500	3.56	0.5010	0.04175
9	1.0775	0.9001	4.25	0.5009	0.04174
10	1.2597	1.0447	5.00	0.5161	0.04301
11	1.4978	1.2500	5.94	0.5010	0.04175
12	1.7968	1.5001	7.13	0.4997	0.04164
13	2.0731	1.7501	7.75	0.5002	0.04168
14	2.3438	2.0000	8.25	0.5000	0.04167
15	2.6146	2.2500	8.75	0.5000	0.04167
16	2.8854	2.5000	9.25	0.5000	0.04167
17	3.1563	2.7500	9.75	0.5000	0.04167
18	3.4271	3.0000	10.25	0.5000	0.04167

Jacobs

The Jacobs Taper is commonly used to secure drill press chucks to an arbor. The taper angles are not consistent varying from 1.41° per side for No. 0 to 2.33° per side for No. 2.
There are also several sizes between No. 2 and No. 3: No. 2 short, No. 6 and No. 33.

Taper	Small End	Big End	Length
No. 0
No. 1
No. 2
No. 2 Short
#
No. 3
No. 4
No. 5
No. 6
No. 33