Differences between CAT40 and NT40 tapers?

Are there any differences between NT40 and CAT40 spindle tapers? I've also seen reference to 40 National Taper, 40 National Taper with Drive Flange, and 40 National Taper with "V" Flange. What are the differences (and why)? Can anyone provide a reference to the actual design specs for the various National Tapers?

Finally, why are 40 National Taper spindles so rare in milling machines sized for the small shop? It seems to be vastly superior (in strength, concentricity, rigidity, and ability to accommodate larger-sized tooling) to R8. Yet, even the 10"x54" class milling machines (costing $7,000+) are fitted with wimpy R8 spindles. Not that I'm ready to buy such a machine...

- Michael

The specs for machine tool tapers are in Machinery's Handbook. lg no neat sig line

I've got NMTB 40 taper on my mill. It uses a threaded draw bar to pull the tool in tight. The CAT taper has a pull stud on the end. So, they are not interchangable even though the taper part is identical. I have modified a few rare CAT 40 holders over to NMTB40. More work than its worth but doable.

The drive flange and V flange are two different ways to keep the holder from slipping. The V flange also has the drive flange collar so they will interchange if you use drive flange.

After using taper 40, I will never buy and R8 machine again. So much better.

Karl

30 Taper is about the smallest that I consider to be solid enough for production work...ie big cuts.

My Gorton Mastermill uses the 30T

Gunner

"Considering the events of recent years, the world has a long way to go to regain its credibility and reputation with the US." unknown

Historical standards tend by nature to self-propagate long after they are obsolete. Especially with tooling.

I muse about this during every tedious R8 tool change.

It depends on the particular taper you are adapting *to*.

I've got both NMTB 30 taper (Bridgeport Boss-3 CNC mill), and generic 40 taper (Nichols horizontal mill, plus vertical head to use the same tooling).

Converting a CAT-40 to the Nichols mill (which only needs the threads for the drawbar and (optionally) the notches) involves:

1) Heating the ball-pull to debond the Loctite so you can unscrew the ball pull. 2) Turning an adaptor which threads into the original threads for the ball pull in the back of te taper, and which provides the orientation collar and the female threads to match the drawbar. (You could make an alternative drawbar which fits through the spindle, is a bit longer, and threads directly into the CAT-40 threads for the ball pull. 3) Loctiting that adaptor into the CAT-40 to keep from experiencing the adaptor unscrewing from the CAT-40 while stuck on the drawbar, thus trapping the drawbar. (My really old Nichols has too small a spindle bore to allow the alternative design, and I *really* did not want to have to try cutting off the drawbar to get the parts out.

However -- converting a CAT-30 (or similar) to fit into the Erickson quick-change head for NMTB-30 tools) requires turning the flange down to a precise thickness so the quick-change lock will work on the flange. (The BOSS-3 has no drawbar.)

You mean for a tool turret to automatically change tools on a running machine? The 'V' is for the gripping part of the tool turret.

And interesting thing is that the taper of an R8 and a 30-taper is identical, as is the larger diameter end of the taper. An R8 taper stops sooner, at a larger minimum diameter. But, with a drawbar, you can hold a 30-taper into an R8 spindle. Unfortunately, you lack the keys to prevent spinning -- both under cutting load and when trying to unscrew the drawbar.

But the Bridgeport BOSS-3 (and later) were often fitted with NMTB-30 taper with an Erickson quick-change head in the spindle.

Enjoy, DoN.

Thanks Larry. I remember looking for the R8 specs in Machinery's Handbook a few years ago and not finding them. So it didn't occur to me to look for the NT specs now. My oversight.

- Michael

Hmmm... I was under the impression that NMTB predated R8. Perhaps I'm wrong.

- Michael

Ok, so I think I understand the differences now, thanks primarily to J Gold's excellent link:

The most obvious difference is that the NMTB tapers have a pilot extension at the small end of the taper, while the CAT tapers do not (in order to accomodate a pull stud). The CAT tapers also have a grooved flange (which I assume is for an automated tool changer).

One thing that's still not clear: in my Machinery Handbook, it shows that the drawbar for NMTB tapers have two threaded portions at the toolholder end: a larger threaded portion (what they call the "Large End"), followed by a smaller threaded portion (what they call the "Small End"). Why is the drawbar stepped in this fashion and how does it work with the NMTB taper toolholder?

- Michael

Because not all tool holders have the same size threads. I ran into this on the Cinci #3 I ran at previous employment. The collection of tool holders there was very old and some of them used the large thread while others used the small one.

Wayne Cook Shamrock, TX

Exactly. I have both styles for my Nichols horizontal mill.

Also for the vertical or right-angle head, which has an interesting drawbar, with a double-ended drawbar and a double-ended nut on the end, so both are reversed to handle the other size NMTB thread.

To see photos of it in both modes, go to my web page on the Nichols mill:

click on the link for the vertical head, and go down to images

dsc02290.jpg

and

dsc02300.jpg

I keep being tempted to make a duplicate of that for the full-length drawbar for the horizontal spindle. As it is, I have one using the smaller thread which I received with the mill, and another using the larger thread which I made of allthread.

I hope that this is some help, DoN.

Because there are two different drawbar threads commonly used in both

30 and 40 NMTB. I have a number of 30 taper holders that use 3/8-16 drawbar threads and others that are 5/16-hummm 20 IRRC. Then the Cat 30 tapers use both of those and a third, 1/2-12

I have 3 draw bars hanging from a rack on my Gorton MasterMill, for this reason.

Gunner

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner

errata...1/2-13

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner

I believe your comment about R8 and 30 taper being the same is incorrect. 30 taper is 3.5"/ft or 7 in 24 whereas R8is about 3.555"/ft. I was helping my neighbour make an R8 spindle earlier and had to check this. The info on the www seems incorrect or misleading, my bridgeport manual shows the taper as 16 degrees 51 minutes, yet some web pages show

16.51 degrees. 16 degrees 51 m>>

O.K.

*Which* was verified? The Bridgeport manual's 16 degrees 51 minutes, or the 16.51 degrees? I presume the former.

O.K. I'll accept that, as you have done the measurements. I had read it some time before, and I simply tried hand-fitting a 30 NMTB into an R8 spindle. It felt free of rocking, but I did not have spotting die at the time, so I did not test it beyond that point.

I had received the information from an article here some years ago, and after a cursory check, took it as valid information. I obviously need to stop that. :-)

An attempt to use a bevel protractor seemed to come out with the same figures, but an R8 collet is a rather springy thing to try to measure.

While _Machinery's Handbook_ has the precise taper of the 30 taper (and the rest of that family) documented, the set of drawings and tables for the R8 (and similar) spring collets does not bother to document the precise taper -- at least in either the 24th edition or the

25th edition.

Enjoy, DoN.