BT versus CAT taper

Also "There are five distinct inherent differences between BT and CAT tapered tools.

The first difference is that the BT shank holder calls for a ground ID in the retention knob cavity. This accepts a retention knob with a ground pilot underneath the shoulder of the knob. This is important because it keeps the pulling force of the spindle on the centerline of the toolholder to minimize any error in the fit between the toolholder taper and the machine spindle. Also, a retention knob with a ground pilot will repeat to the same position when you remove it and then replace it again. A CAT shank retention knob will not. This is a benefit in maintaining balance in high-speed applications.

The second difference is that the BT shank holder is manufactured for symmetry. Both drive keys have the same width and depth. A CAT shank toolholder has drive keys that vary in width and depth, and, therefore, a correction mark must be made in the smaller keys to compensate for the difference. This makes the BT shank toolholder easier to balance.

The third difference is that the CAT shank toolholder is governed by the ANSI standard, which calls for a relief cut under the flange of the toolholder of 5/8" width. This is a requirement so that there is no interference with carousel-type tool changers. This specification unfortunately weakens the design of the CAT shank. Without the relief cut, in the case of BT, the toolholder can be shortened and a thicker diameter can be maintained under the flange for increased rigidity.

The fourth difference is that all of the dimensions on the BT shank toolholder are in metric. This includes the threads in the retention knob cavity, and the keys.

The fifth and final difference is the slot in the flange of the BT shank toolholder is off-set, plus the flange is thicker. On the CAT shank toolholder the slot in the flange is centered."

The preceeding quote was taken from:

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Some general information about tapers can be found on
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Reply to
J Gold
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aaarrrggghhh!!!

ok, now that I've said it - I have this Abene mill - it has a #40 taper, so I bought a pile of #40 tool holders. Some (about 2 out of

5) work properly, the remainder have the wrong draw bar thread. So, I'm imagining that I have two different types of holders - it seems by looking around that BT and CAT are the same except for drawbar thread (metric for BT, inch for CAT) -- is this correct?

If yes, anyone wanna trade? Bill

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Reply to
William B Noble (don't reply t

Bill..my big old Gorton MasterMill is 30 taper, but Ive got a dutch mixture of CAT, BT, NNT, and Standard tool holders.

And a nice little rack on the side of the mill I made to hold the 3 draw bolts I made. One for each type of thread, and color coded with

99c a can rattle can paint on the hex at the top.

I got about 6' of .6 Stressproof, and made em up in about an hour. Threads and all.

Tis quite simple to do. And I did the same for my Clausing 8540 horizontal miller, also 30 taper, so I can use all the various tool holders on both machines. The Clausing draw bolts were made of Mystery Metal, .50..cause I ran out of Stressproof.

All work just hunky dorey.

Thread the end of your rod to the right thread. Drop it into the spindle. Screw it into a tool holder sitting on your table, about half way. Pull the rod up and hold the tool holder up in the taper.

Make up some hex nuts from hex stock. Slide it over the rod and down till it touches the top of the quill. Mark with Magic Marker. Remove tool holder, remove rod, cut off at mark, weld hex stock to rod, or cross drill and pin.

Repeat as necessary.

The aim of untold millions is to be free to do exactly as they choose and for someone else to pay when things go wrong.

In the past few decades, a peculiar and distinctive psychology has emerged in England. Gone are the civility, sturdy independence, and admirable stoicism that carried the English through the war years . It has been replaced by a constant whine of excuses, complaints, and special pleading. The collapse of the British character has been as swift and complete as the collapse of British power.

Theodore Dalrymple,

Reply to
Gunner

Its not only the tread is different, the design of the ring that the toolchanger grabs is different too. Are you looking for BT or Cat 40?

John

Reply to
john

According to William B Noble (don't reply to this address) :

I believe so.

But -- there are also NTMB 40 taper which has a flat flange instead of the thicker V-grooved ones on both the BT and CAT. All three should be perfectly usable on your machine (assuming that it does not have a tool changer as part of it, which given your use of a drawbar suggests that it does not).

I use 40-taper in my ancient Nichols horizontal mill, and can use all three styles.

The NTMB 40 has a cylindrical projection from the small end of the taper. And it can have either of two drawbar threads.

The BT and CAT instead tend to have a ball stud screwed into the taper threads. (And, these are often retained with Loctite, so you need to heat them to unscrew the studs.)

I've machined up collars which screw into the CAT-40 or BT-40 holders and which have the smaller of the two common threads at the free end, so I can use these in my Nichols mill. (The drawbar is double-ended, with small thread on one end and large thread on the other.

The nut on the end of the drawbar is also double-ended, with a female thread on each end to match on eof the ends of the drawbar, so you reverse both drawbar and nut to switch between threads. You could duplicate this, or you could simply make another drawbar for the other size.

Look at _Machinery's Handbook_ (25th edition, page 920) which will give you the details and dimensions of the taper which I use. (ANSI B5.18-1972,R1991). (It will be on a different page in later editions of _Machinery's Handbook_.) This should suffice to tell you how to make your own extension shanks as I did. (Loctite the extension, so it does not come out instead of the drawbar when you want to loosen it.)

I can't find the specs for either the CAT or BT tapers in my issue of _Machinery's Handbook_, but the actual taper is the same. The differences are in the flange and the drawbar or draw-stud threads.

Good Luck, DoN.

Reply to
DoN. Nichols

He's actually looking for standard American or NMTB 40. His mill isn't CNC so the ring doesn't really matter.

Wayne Cook Shamrock, TX

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Reply to
Wayne Cook

According to john :

[ ... ]

I *think* that his mill is not CNC, and thus does not have a toolchanger. For that, just making alternate drawbars should be sufficient.

Enjoy, DoN.

Reply to
DoN. Nichols

well, I went out to my garage after a good night's sleep and did some more experiments trying to understand what fit and what did not - this is very odd, but I think I'm understanding it now. So, some more "facts", such as they are:

  1. this machine has a captive drawbar, so it's a realatively bigger deal to change drawbars for a different tool holder.

  1. a 5/8X11 bolt fits into every tool holder - the ones that fit and the ones that don't fit.

so, my conclusion is that this is a thread tolerance problem, the ones that don't fit have the female threads undersized compared to the ones that do fit. So, I will see about enlarging the threads in the "don't fit" tool holders a little bit and then if I am lucky, all will be well.

I've never seen this happen before, but then again, there's a lot of things I haven't seen. I know it's theoretically possible....

I intend to modify the offending holders rather than the drawbar on the theory that the Sweedish machine is probably more accurate than whatever made the holders and therefore should remain the standard.

remarks anyone?

(yes, this is an interesting learning experience - thanks for the commentary and advise) Bill

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Reply to
William B Noble (don't reply t

Actually this is easily fixed. There's just a threaded collar holding it in place. Mine never had it in there from the first time I saw it. While nice in some ways it's not totally necessary and would be a hinderance in some cases like this.

Possible though another possibility could be slightly buggered threads on the drawbar. It might not hurt to take it out so you can get a good look at the threads.

Definitely.

The holders might be to hard to modify but you won't know till you try.

Wayne Cook Shamrock, TX

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Reply to
Wayne Cook

AH!! major difference...

They may..may be hardened, so proceed carefuly and use lots of earl

If the Cats are too short..its maybe possible to make up an extension..though ID of the quill may prevent this..or not.

How is the draw bar held captive? I dont think Ive ever seen one that couldnt be easily removed.

The aim of untold millions is to be free to do exactly as they choose and for someone else to pay when things go wrong.

In the past few decades, a peculiar and distinctive psychology has emerged in England. Gone are the civility, sturdy independence, and admirable stoicism that carried the English through the war years . It has been replaced by a constant whine of excuses, complaints, and special pleading. The collapse of the British character has been as swift and complete as the collapse of British power.

Theodore Dalrymple,

Reply to
Gunner

following up, for those who chimed in - I removed the drawbar (held in place by a LH threaded nipple - took a while to figure that one out) - took drawbar and holders to a friend who had a good thread mic and we found that the drawbar thread was about 1.5 thousandths too large - turned it down with a nice sharp 5/8X11 die and all is well.

thanks for the help and advise. Bill

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to contact me, do not reply to this message, instead correct this address and use it

will iam_ b_ No ble at msn daught com

Reply to
William B Noble (don't reply t

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