Milling Machine Tapers	Questions? Comments? Email me
		updated 29-sep-00 20:42 This page created by Rick Dulas

This is an attempt to clarify some of the murkiness surrounding Milling Machine Tooling Tapers. Given the number of terms used to describe Milling Machine Tapers, it may be surprising that there are really just a few tapers in widespread use. To make it easy for you, many manual milling machines use "R-8" tooling, but CNC or larger machines usually will have some other toolholder taper. One of the things to recognize is that a toolholder consists of 2 sections separated by the gage line. The taper fits into the spindle allowing the machine spindle to transfer rotary motion to the tool which is held in the toolholder portion. The toolholder section ... holds the tool.

So a toolholder has a 2 part specification, taper and tool. For instance, an NMTB #30 collet chuck and an NMTB 1/2" endmill holder would fit the same machine, but might not hold the same tool. Conversely, the same NMTB 1/2" endmill holder and a Universal Kwik-Switch 200 1/2" endmill holder will hold the same tool, but WILL NOT fit into the same machine. If you look at the drawings below, you'll see only the taper portion of the toolholder, not the toolholder portion, since we are dealing Milling Machine Tapers, not toolholders. But since you were nice enough to read this far, here is a link to a toolholder family.

So why are you here reading this page?

1. You have a machine and don't know what kind of taper it uses.
2. You have a toolholder and don't know what kind of taper it is.
3. You don't know anything about toolholders and tapers.
4. You were surfing the NET and stumbled across this page. 

Identify the Taper:

Tapers, like most things in life, can be separated into 2 groups. Those with ears and those without them. If they have ears, they fall into the Kwik-Switch or Rapid-Switch family. If they have a collar or flange instead of ears, they are either single collar or dual collar tapers. The single collar tapers go by lots of names, most notably NMTB or Erickson Quick Change. There are two common dual flange types: V-flange and BT-flange. V-flanges are often referred to as Caterpillar V-flanges. Somebody said: "Caterpillar V-flanges use inch threads for the retention knob and are used to hold inch-dimensioned cutting tools. BT-flanges have metric threads for the retention knob, but their adaptors can be designed to accommodate a wide range of inch-dimensioned cutting tools. BT-flange holders are widely used in Japanese and European made machining centers."

There are some size definitions from the ANSI standard and the relationship of machine size to NMTB taper used. They say "Larger machines use toolholders that have larger shank taper numbers." (Kinda' makes sense in an engineering sort of way.)

All of the major tapers, except the Universal Kwik-Switch family, use the 3 1/2" in 12" model of the NMTB. Of course, the Europeans claim that this is really 7 in 24, but why argue. While the taper per se may not help much, the mass might. A 3/8" endmill #50 NMTB toolholder is about 9 pounds of serious metal compared to 3/4 of a pound for 1/4" endmill #30 NMTB toolholder. One might almost say "it is dainty" by comparison.

Identify the Machine:

The above assumes that you are holding a chunk of metal in your hand. What do you do if you have a machine with no tooling and would like to get some? (After all, there is no sense in letting a multi-thousand dollar piece of machinery sit idle just because you aren't sure what you've got.) Ask an expert? "What a great idea!" However you need to keep in mind that machine tools are not commodity items produced on high-volume assembly lines. A machinery dealer notes in the year 2000, that

Hardly what one would call high volume production compared to automobiles or washing machines. Milling machines seem to much more like Semi-Truck Tractors. You can go to the factory and get it made "any way your heart desires". Unless your expert is live and in-person, take what you hear with a grain of salt. The odds are that he may never have seen a  fill in the blank  just exactly like yours.

Beg, borrow or steal any documentation you can find. While this will get you on the path to enlightenment, it probably won't answer all your questions. Go out and look in the maw of the machine. The spindle will exactly opposite of the toolholder. What is void in the spindle is solid in the toolholder, and vice versa. Take some measurements, make some simple drawings, get more advice. When you do buy toolholders that don't fit your machine, mention them on Rec.Crafts.Metalworking, someone will take them off your hands. Above all, treat this as an adventure in the pursuit of knowledge, because goodness knows,

"This is a not-for-profit operation."

Single Flange Tapers

NMTB - National Machine Tool Builders' Association, 1927. (Also known as DIN 2080 / IS 2340 SHANK)
This is the granddaddy of tapers, as evidenced by the numerous names it has. You'll see it called Quick Change, NMTB, MM, National Standard, American Standard Machine Taper, ISOXX, & QCXX... The American Standard Steep Machine Taper (ASA B5.10-1963) defines 12 tapers: #5, #10, #15, #20, #25, #30, #35, #40, #45, #50, #55, #60. Those numbers in bold are the "Preferred Series" while the others are in the "Intermediate Series". ANSI mentions six taper shank sizes including #30, #35, #40, #45, #50, and #60. For all the sizes the taper is 3 1/2" per foot.
	Shank Slot A B C 30 16.1 [.634] 31.75 [1.250] 68.4 [2.75] 1/2-13 40 16.1 [.634] 44.45 [1.750] 93.4 [3.75] 5/8-11 50 25.7 [1.012] 69.85 [2.750] 126.8 [5.12] 1-8

DUAL FLANGE TAPERS

The following dual flange tapers are alleged to be both different and the same. You'll see the CAT flange referred to as DIN69871 as well as ISO 7388-1, and the BT flange referred to as ISO 7388-1. Does that make the DIN69871 the same as ISO 7388-1? Your guess is as good as mine. They do all have the same taper and they are all about the same size for the same taper number.

BT Flange
AKA: JMTBA MAS-403 "BT" JIS B 6339 - 1986 JIS B6339 - 1992 ISO 7388/1 - 1983
	MODEL D1 D2 t1 t2 L1 L2 L3 L d1 d2 G BT30 46 38 20 2 48.4 34 24 70.4 31.75 12.5 M12 BT40 63 53 25 2 65.4 70 30 92.4 44.45 17 M16 BT50 100 85 35 3 101.8 90 45 139.8 69.85 25 M24

DIN 69871-A TAPER
AKA: BT? CAT? V-Flange?
	MODEL D1  D2 t1 t2 L1 L2 L3 d1 d2 M max.  G 30 50 44.30 15.9 3.2 47.8 33.5 24 31.75 13 45 M12 40 63.55 56.25 68.4 42.5 32 44.45 17 50 M16 50 97.5 91.25 101.75 61.5 47 69.85 25 80 M24

Universal Kwik-Switch

Universal Kwik-Switch
The Kwik-Switch is supplied as alternative tooling in Bridgeport and other machines. The equivalent to the NMTB #30 is the 200 series which has more mass and a more positive lock. This taper style is also made by Collis who call it Rapid-Switch.
	Kwik-Switch Size A B C E F H J K L M 100 .875 1.44 0.16 0.312 0.250 1.12 1.56 0.375 1.06 0.68 200 1.312 2.50 0.22 0.375 0.312 1.75 2.12 0.500 1.68 0.97 300 1.625 2.94 0.28 0.438 0.375 2.00 2.50 0.500 1.94 1.22 400 2.250 3.62 0.34 0.500 0.438 2.81 3.25 0.625 2.75 1.75

Other Toolholding Information

Hollow Shaft Taper (HSK) Tooling
Position before clamping Spindle HSK - Tool	(after) Face and taper contact position Spindle HSK - Tool
This is just thrown in as an added attraction. It is another way to hold a tool tightly onto/into the spindle.

Brown & Sharpe
Range from 1 to 18, taper is approximately 1/2" per foot. B&S 9 and 11 seem to be the most common. But I have no other information on this taper.

R-8 Also refered to as M1TR taper
This is not truly a taper as defined by Machinery's Handbook, since it is held in place by a drawbar. Picture a long 7/16"NF bolt leading down through the spindle, threading onto the R-8 toolholder.

Significant chunks of this information were lifted from the following:
		and from Tooling Systems Division
As well as Machinery's Handbook 19th Ed. and countless other sites. But any errors are my own.