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Big+ CAT40 vs BT40 on a new machine (in the USA)

mutiny

Cast Iron
Joined
Jan 27, 2019
Location
Raleigh
"Hypothetical" scenario for you all. You're speccing out a new machine and have a choice of either CAT40 or BT40. Both would be dual contact. You live in the US. You care about quality tooling. You use a mix of imperial and metric tooling. You have no other machines with either interface in the shop, so "get what you already use" does not apply.

What do you choose and why? (And is it even a debate worth having?)
 
Most tool holder manufacturers based in the USA will have much more stock of dual contact CAT40 tool holders than BT40 dual contact tool holders. Why keep stock of a product that does not move? I probably sell 30:1 of CAT40 dual contact tool holders vs BT40 dual contact. Sure some of that may be the limited offerings I have in BT40 dual contact vs CAT40 dual contact. But the truth is I barely get any requests for a custom BT40 dual contact compared to CAT40 dual contact.

Anyway that is my 2cents.
 
My gut reaction, and I have no experience with this, would be don't get the one that will fit in your other machines. That way you are not tempted to mix your regular tooling and you dual contact tooling. I don't know if that will matter, good luck.
 
As someone who buys a lot of Japanese and European holders, I would absolutely opt for BT40. AFAIK CAT40 is a USA only affair. Also the asymmetrical design of CAT40 seems really stupid, since balancing is now so critical. :nutter:
 
As someone who buys a lot of Japanese and European holders, I would absolutely opt for BT40. AFAIK CAT40 is a USA only affair. Also the asymmetrical design of CAT40 seems really stupid, since balancing is now so critical. :nutter:

I'm glad I'm not the only one who had this thought, tbh. On the one hand: relatively inexpensive, quality collet holders in CAT (ER and SK) from MariTool. On the other hand, extremely high quality shrink, hydraulic, etc holders from Japanese and European manufacturers in BT.
 
I'd go with option C, HSK63A :D

^^^By far my favorite medium sized interface.

But FWIW HSK63 is definitely less rigid than dual contact 40 taper at lower RPMS. A dual contact 40 is pretty good for middle of the road. The rotating mass is small enough that you can get some really fast spindles, but it's stout enough that the spindle interface is more robust than the machine for most 40x20 applications.
 
Yea CAT seems to be very american for example MST tools barely have any CAT interfaced tools, most are HSK or BT.

Personally I would 100% go with HSK if I could
 
I prefer CAT spindles for the tooling availability and cost. Also, Full Contact (Big-Plus) is a must. After seeing it in action and demo-ing machines with it, I'm sold.
 
That's a tough one. CAT is certainly prevalent in the USA. But BT is better, being symetrical.

If you said that you used "all metric" tooling, then BT hands down.

Metric & Imperial - It's a toss up.



Maybe get quotes on some comparable CAT & BT tools from reputable BT40 Dual-Contact makers and ask the most important question - LEAD TIMES...?
 
Makes absolutely no difference if the holders are symmetrical. Material is not perfectly homogeneous. BT40 or CAT40 need the same amount of attention when balancing. If someone makes a BT40 tool holder and all holes are perfectly in center and all features symmetrical it will be hit or miss if it passes G2.5 @ 20,000 rpm spec.
 
Saunders (I know, I know) just did an interview with a guy from Big Kaiser who actually talks a lot about why CAT/BT is better than HSK in a lot of applications.
 
All else equal, a CAT40 spindle will also command higher resale value in the States.

Resale might be an afterthought for most, but it's a safety net for the short term. For the long term, it makes it easier to trade up for new equipment before your existing equipment goes obsolete, and before your machine gets plagued with nagging issues like clogged lubrication lines, bad encoders and sensors, etc that will nickel and dime you to death.
 
No personal knowledge on which is actually better, but when we bought our Yasda PX30, we were told by multiple manufacturers, (Big Kaiser, Zoller, Yasda) that BT was definitely superior to CAT. We buy only Big Kaiser, Big+ holders for that machine, and haven't had any issues getting tooling.
 
No,

CAT40 the taper is slightly longer than BT40. So the stem length for a CAT40 retention knob is @ .115" shorter than a corresponding BT40 retention knob. Shorter stem is stronger that a longer stem if a crash should happen. Symmetry is a mute point, so CAT40 wins. Be cautious when listening to some salesman, they only know what the've been told. I make em.
 
No,

CAT40 the taper is slightly longer than BT40. So the stem length for a CAT40 retention knob is @ .115" shorter than a corresponding BT40 retention knob. Shorter stem is stronger that a longer stem if a crash should happen. Symmetry is a mute point, so CAT40 wins. Be cautious when listening to some salesman, they only know what the've been told. I make em.

Wish I could like this a hundred times, as well as your post about the influence of material homogeneity on balancing. What Frank says you can take to the bank.
 
Something I encountered - The BT spec ends at the flange, while the CAT spec includes a reduced diameter protrusion from the flange toward the tool. This allows more freedom in designing the BT tools, and BT toolchangers. You see BT tools that are full flange diameter leading
outward but never a CAT. Can also make converting from one toolchanger to the other complex.

Machine Tool Shanks (Tapers)

Tapers_Cat_1.jpg
Tapers_BT_1.jpg
 
Yes,
CAT40 "requires" a 1-3/4 diameter at least to 1-3/8 gage length. 99.99 % of machining centers less than 30 years old do not care for this provision. Too much trouble converting a BT40 machine to CAT40 if they need to grab on this diameter as well. So you have the same freedom for both. I make plenty of CAT40 tool holders that do not adhere to this specification. Not 1 problem.

For a while now converting a machine from BT40 to CAT40 or the other way around is just a matter of changing the tool changer arm grippers and a Z offset if the different gripper changes the tool holder position.
 








 
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