Machine Tapers

In the design of machine tools there is a need for users to be able to quickly and easily install or remove particular cutting bits or other accessories from the powered rotating spindle of the machine tool. One example is a lathe headstock, which has a rotating spindle to which one may want to mount a spur drive. Another example is a drill press on which one may want to mount a bit, a chuck, etc.

Several options exist: the machine tool can present a threaded spindle, to which accessories are screwed. The machine tool may have a permanent chuck. A simple, low cost, and versatile option is to hollow out a truncated conical void in the rotating spindle, coaxial with the axis of rotation. Tools or accessories can then have a mating male conical shaped shank, which precisely fits into the void. The pressure of the spindle against the workpiece serves to drive the tapered shank tightly into the tapered receptable. The friction across the entire surface area of the interface provides a suprisingly large amount of torque transmission, so that splines or keys are not required.

This system is known as a "machine taper".

Method of Specification; Overview of Families

There are multiple different standard tapers, each differing in (a) the diameter at the small end of the truncated cone ("the minor diameter"); (b) the diameter at the large end of the truncated code ("the major diameter"); (c) the axial distance between the two ends of the truncated cone.

The standards are grouped into families. The most famous family is the "Morse taper", which comes in 8 varieties, from "Morse 0" (two inches from end to end) to "Morse 8" (10 inches from end to end).

It is noteworthy that even thought one could design a family of tapers that all have the same included angle (e.g. the Foobar taper, from the 2" long Foobar-2 to the 100" long Foobar-100, all of which have a 5 degree included angle), the actual families of tapers in existence do not exhibit this design feature. Morse tapers, for example, taper at anywhere from 0.04988 inches of diameter per inch of length (for the Morse 1) to 0.05262 inches of diameter per inch of length (for the Morse 5).

One of the first uses of tapers was to mount Drill_bit#Morse_taper_shank_drills directly to machine tools, although later Chuck_%28engineering%29#Drill were invented that mounted to machine tools and in turn held non-tapered drill bits.

Details of Use

Bits or accessories are inserted into a tapered receptacle and pushed or twisted into place. They are then held by friction.

Tapered shanks "stick" in tapers best when both the shank and the receptacle are clean. Shanks can be wiped clean, but receptacles, 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 tapered receptacles either by inserting a drift punch axially from behind, and tapping the tapered shank tool out of the receptacle, or - if the tapered shank tool is so designed - inserting a wedge shaped block of metal called a "drift" is inserted into a rectangular shaped cross hole through the shank, and tapped. As the cross section of the drift gets larger as the drift is pushed further in, the result is that the drift, bearing against the foremost edge of the tang receptacle, pulls the tapered tang out.

Families of Tapers

Morse

The Morse taper, was invented by Stephen A. Morse (also the inventor of the twist drill) circa 1864. Since then it has evolved to encompass smaller and larger sizes, and has been adopted as a standard by numerous organizations including International Organization for Standardization as ISO 296:1991 Machine Tools -- Self-Holding Tapers for Tools Shanks, and DIN as DIN 228-1:1987-05 Morse tapers and metric tapers; taper shanks.

Morse tapers come in seven sizes identified by number -- #0 through #6. Often this is abbreviated as MT followed by a digit, for example a Morse taper number 4 would be MT4.

Morse tapers can have two types of ends:

  • tang (illustrated) to facilitate removal with a drift
  • threaded to be held in place with a draw bar
The taper itself is roughly 5/8" per foot, but exact ratios and dimensions for the various sizes of tang type tapers are given below.
Morse Taper Dimensions (mm)
Image:MorseTaper-2.png
Morse Taper
Taper
A
B (max)
C (max)
D (max)
E(max)
F
G
H
J
K
0
19.212:1
9.045
56.5
59.5
10.5
6
4
1
3
3.9
1°29'27"
1
20.047:1
12.065
62
65.5
13.5
8.7
5
1.2
3.5
5.2
1°25'43"
2
20.020:1
17.780
75
80
16
13.5
6
1.6
5
6.3
1°25'50"
3
19.922:1
23.825
94
99
20
18.5
7
2
5
7.9
1°26'16"
4
19.254:1
31.267
117.5
124
24
24.5
8
2.5
6.5
11.9
1°29'15"
5
19.002:1
44.399
149.5
156
29
35.7
10
3
6.5
15.9
1°20'26"
6
19.180:1
63.348
210
218
40
51
13
4
8
19
1°29'36"

Brown and Sharpe

R8

NT 30 (int30)

NT 40 (int40)

NT 50 (int50)




External Links

Beautiful Iron Overview of Tapers