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View Full Version : Difference Between Cat-40 and BT-40?



RTPBurnsville
05-15-2007, 03:53 PM
Hi,

I have been researching to buy a CNC mill for my home shop and have a question that maybe someone here can help me with. What is the difference between a cat-40 and a bt-40 spindle? Are there advantages to one vs the other? It appears that a cat-40 is more popular, is that a true statement? The Haas MiniMill for example let's you order either for the same price and I am clueless at the moment to make a choice.

Thanks,
Robert

Forrest Addy
05-15-2007, 04:22 PM
Both BT and Cat 40 has a 40 MMT cut flush at the small end. The BT thread is metric and the Cat 5/8-11 for their respective retention plugs and the tool change flange is slightly different too. No, they won't interchange. You got a Cat 40 machine you need Cat 40 tooling.

Mark McGrath
05-15-2007, 05:05 PM
I don`t like to contradict you Forrest but you can get CAT`s with a metric thread.I have just bought a Mazak VMC with a CAT spindle nose and no tooling and as I need at least thirty toolholders and as I was not sure myself about the differences between BT`s and CAT`s have just spent a lot of time finding out.The main differences are the BT has a thicker V flange than the CAT and the radial depth of ONE of the cutouts for the drive dogs to enter on the flange of the CAT is less than the opposite one.The BT has both cutouts the full depth.The CAT flange also has a V cutout on the edge of the flange which I assume is used to orientate the holder in relation to the dogs.
A BT holder will fit a CAT spindle but not vice versa.Obviously there would also be toolchanger issues.
As it turns out I have some CAT40 holders which I have been using on a manual turret mill which only has one drive dog on the spindle.I had wondered occasionally why they only fitted one way but as they did fit I didn`t bother investigating any further.I also use BT40`s and INT40`s in this machine just have a selection of drawbars.
Mark.

IOWOLF
05-15-2007, 05:48 PM
Both BT and Cat 40 has a 40 MMT cut flush at the small end. The BT thread is metric and the Cat 5/8-11 for their respective retention plugs and the tool change flange is slightly different too. No, they won't interchange. You got a Cat 40 machine you need Cat 40 tooling.

I agree with Mark ,I have Cat 40, bt 40, int 40,and use them with diff. draw bars in the same mill,though it is a '30's era Cincinnati horizontal mill.

Forrest Addy
05-15-2007, 07:57 PM
My bad. I bought a buncha machine for the Gumint back when. I'm repeating back the assumption I made from info at the time. The tapers are the same but the differences in in the details I mentioned. If practical experience has shown that they can be used interchangelbly in a CNC mill's tool changer I can accept that.

If they're used with a drawbolt all that's needed is drawbolts to suit.

Mark McGrath
05-15-2007, 08:09 PM
Forrest,I didn`t say they could be used in a toolchanger without issues arising,I`m only disagreeing with you on the thread.They certainly could not be mixed.It might be possible to run BT`s in a Cat changer if the height problems were addressed.I`ll be sticking with CAT`s for my spindle.Looking on Ebay there are lots of CAT holders on the American site plenty BT`s on the UK one but no CAT`s.Price here for a CAT40/ER32 collet chuck with Mazak pull stud is about $60 new.This is one part that has got considerably cheaper over the years,a few years ago you would have been looking at $400 in the UK.

RTPBurnsville
05-16-2007, 07:56 AM
Thanks guys..... Looks like I'll go with cat-40 tooling being that appears to be the most used here in the states.