View Full Version : CAT-30 versus R8 spindle taper

03-21-2009, 09:17 PM

I came across this old topic: http://www.cnczone.com/forums/archive/index.php/t-28781.html and I would like to add my 2 cents to the collection.

The original subject dealt with the justification for selecting a NT30 spindle over a R8 spindle taper. After reading through all of the responding post I likened the experience to that of watching the knife throwing act at a carnival. The answers were so close to the subject but they never as much as nicked the subject.

I own machines with R8 spindles and others with NT30 and both spindle configurations hold tight tolerances in all axis. This is going to hit you like a hammer when I explain the justification for selecting a NT30 spindle over a R8 spindle taper, but wait just a minute here, I think that I have already let it slip out.

Oh well what can I say? After all I'm,

03-21-2009, 10:35 PM
I'm in full 100% agreement with what you said ! Your nutz and all your knives are scattered out in the tall grass ! You just had a weird way of saying it !

03-22-2009, 01:09 AM
NT30 ejects without the hammer.

03-22-2009, 09:04 AM
Ooops, here we go again.

Both types have effectively the same taper angle, which theoretically is a none self-holding angle. I have used both types and have found on occasion that it is necessary to tap the toolholder out with both. I think this may have more to do with the precision of the mating surfaces than it has to do with the different style.:)

Just a thought

03-22-2009, 12:52 PM
It all has to do with knifes and nuts?????:)


03-22-2009, 12:56 PM
They're not quite the same, Phil, though they may be close enough as not to matter:

R8 = 16 degrees 51 minutes.
CAT, BT, NMTB = 16 degrees 35 minutes 40 seconds

At some point, any taper may require a little extra effort to release. But, CAT, BT, and NMTB all release more reliably than R8.

It's a moot point, though. The only application where it matters is with an ATC, and all of these taper styles will employ some positive pressure on the toolholder to make sure it releases. In other words, an air cylinder is driving down the drawbar whether that is threaded or engaging a retention knob.



03-23-2009, 08:19 PM
Bob, all the holders have a tendency to stick. i even had a cat 40 holder stick in my fadal spindle and i know thats alot better machined and assembled than any chinese mill. the real difference in the sticking i think comes from the differences in thermal expansion of the materials used. i've had R-8 collets stick and need some tapping and i've had the solid holders come right out.

really it comes down to the application and ultimately i think the NMTB 30 has more surface area in contact with the spindle. is this better? maybe, it also seems to have more of the holder withing the area where the bearings are.

03-23-2009, 10:03 PM
The one big thing that you are all leaving out is contamination with grit and sticky dried coolant that will hold the grit. Then, the grit will cause the formation of irregularities in the holding portion of the taper and ANY Holder will eventually get very stubborn and consider the damage is magnified at the spindle as all of the damaged holders imprint on the spindle. This is a constant consideration with any tooling system which resides in a tool carousel. Then it really boils down to the fact that this is an IH thread and so any advantages or lack there-in should be reflected as we see them for OUR mills. I personally see no real advantage to a larger than R-8 system as I have seen the mill buck and jump with a large end mill. The biggest difference with the 30 taper holder is that it lends itself well to auto or power tool change and there are much larger cutters available for the 30 + holders. What advantage would it be to mount a large cutter if you couldn't put the horse power and force to it to move a lot of material out of the way ? I am not saying it is impractical but for the money spent it is more practical to just tool up the R-8 and program smart ! That reminds me of the picture I saw recently about someone trimming some aluminum part with a huge scallop roughing end mill, I thought it was hilarious ! If someone wants the nt30 taper for what ever reason then Gene has Chinese tooling available and can make the conversion for them and they can certainly run with it and do what ever it is they are going to do. I guess my point is why is everyone throwing there knives out into the tall grass chasing this around when it really boils down to the weakest link in the system and that means rigidity limitations to make it productive enough, to spend the extra money. Sure, the nt30 is stronger to some unknown extent over the r-8 but I'm convinced that both will do the same amount of work in the IH mill, there is only so much twist and push available for the material removal rate achievable.