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  • Mill Tapers

    Had a look at the LMS comparison chart of mini mills. Seem to be a choice of MT3 or R8. R8 (according to Wikipedia) is a Bridgeport design specifically for milling vs the MT which seems to be a "universal" taper.

    That said, practically, is one better suited than the other for a milling machine? Is more tooling available "out there" for one vs the other? Any appreciable difference in costs of MT3 vs R8?

    Any other thoughts you wish to pass along are welcome.

    Thanks for

  • #2
    The R8 will hold cutters directly.
    The MT3 you need a collet holder, which means you have more overhang.

    Benta.

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    • #3
      MT#3 collets are available, but MT collets in general do not grip as well as R8, and R8 is more of a standard than MT for milling machines. Given the choice, R8 is the better of the two.
      Jim H.

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      • #4
        Originally posted by JCHannum
        but MT collets in general do not grip as well as R8,
        Huh? R8 isn't even a locking taper, and is a relatively feeble way to hold anything.

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        • #5
          Huh? R8 isn't even a locking taper, and is a relatively feeble way to hold anything.
          Feeble....yeah...compared to the NTMB (and CAT etc) tapers, perhaps. However, the morse tapers hold no competitive advantage over the R8. Morse tapers are *not* self holding in a milling machine where it sees side loads. There's far more tooling out there in r8 and R8 collets are capable of holding larger end mill shanks than you can fit in an MT3.

          I think the folks who find the R8 inadequate are the same folks who are more often than not stretching the limits of the mills whose spindles are ground for an R8. Its also important to separate out the holding ability of collets vs. end mill holders from the issue of the taper of the same collets and end mill holders.

          I have the HF mini-mill with the R8 spindle. I am glad I went that route. I now own a Bridgeport knee mill and the tooling is interchangable.

          Do not let the fact that Bridgeport may have invented the taper many decades ago lead you to believe that its in any way proprietary....far from it. Browse any tool catalog and you will find plenty of things with an R-8 shank that are not available in another taper. If you have one of the other tapers, you have to buy the item with a straight shank and put it in an end mill holder....extending the length, flexibility, and force on the spindle bearings as well as reducing precious work envelope (especially on such a tiny mill).

          Paul
          Paul Carpenter
          Mapleton, IL

          Comment


          • #6
            Originally posted by Dunc
            R8 (according to Wikipedia) is a Bridgeport design specifically for milling vs the MT which seems to be a "universal" taper.
            The usage has, historically, evolved somewhat, so the "universality" of one taper now has little practical use. Locking tapers were originally standardized as a way to mount tools directly to spindles. So drill bits and similar tools were made with tapers on one end. This worked well enough if the application involved an axial force which kept the taper locked in place. Not too bad for drilling, but not so good for vertical mills. So collets with drawbars appeared, originally to fit in these older locking tapers. The self-locking geometry was no longer very important, as the drawbar did most of the work, so soon other (non-locking) tapers appeared for use with collets and drawbars - not for self-locking applications.

            A spindle with a Morse taper isn't "universal" in any practical sense, since you can't just bang in tools with Morse tapers on the ends (like, say, drill bits, or lathe centers). The drawbar is in the way and those tools won't fit. Your tools need the appropriate taper and a threaded hole for the drawbar, OR they need to be a shape (usually a cylinder) which a collet for that taper can grab onto. For special applications you could remove the drawbar and use a solid Morse socket in a Morse spindle, but generally that's not too useful. I've done it maybe once, ever.

            In the US, for mill use R8 tools and collets are far more common than Morse.

            Comment


            • #7
              Originally posted by pcarpenter
              Feeble....yeah...compared to the NTMB (and CAT etc) tapers, perhaps. However, the morse tapers hold no competitive advantage over the R8. Morse tapers are *not* self holding in a milling machine where it sees side loads.
              Quite right, a Morse taper without a drawbar is not adequate for milling machine use. I only mentioned the locking property of the taper because I found the above claim that Morse tapers don't grip as well as R8 to be, basically, incredible. And the reason why is simple geometry - which happens to be the same geometry which makes some tapers locking, and some not.
              I think the folks who find the R8 inadequate are the same folks who are more often than not stretching the limits of the mills whose spindles are ground for an R8.
              As for that, I can't say. All I can say is that I have occasionally had cutting tools move axially when held in R8 collets, and don't happen to have had the same problem when using collets with more gradual tapers. While hardly proof of anything, those experiences inspire some skepticism when I see claims about the mystical properties of the R8 taper.
              Its also important to separate out the holding ability of collets vs. end mill holders from the issue of the taper of the same collets and end mill holders.
              Yes, separate issues entirely.
              Last edited by rantbot; 05-25-2008, 01:12 PM.

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              • #8
                First off I would go with the R8, its cheap and very common.

                You can get MT endmill holders, they are rock solid.

                One little warning with MT is never over tighten the draw bar , They will get stuck so damn tight its not one damn bit funny. R8 is far less prone to getting stuck.

                You can get away with a tight draw bar with an R8 but you do that with a MT you will be sorry you did.

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                • #9
                  Self releasing vs self holding has little to do with the gripping power of the collet. DA, TG and ER collets are all self releasing. The R8 has better holding power than MT collets coupled with the fact that once sufficient force has been applied to hold the tool, it can be removed without destroying the spindle bearings.

                  Bridgeport initially used MT collets on their early heads. Recognizing the need for improvement, they developed the R8. It has been an industry standard since, replacing the MT and B&S collets in most cases. While it might not be the best, it represents significant improvement over MT collets.
                  Jim H.

                  Comment


                  • #10
                    Here's the real issue. R-8 holders are in plentiful supply, generally cheaper, and considerably stiffer since they are 1 1/4 dia on the big end Vs 0.938 for the #3 Morse.

                    If you have a choice of either, lunge for the R-8.

                    If you have a chance at a #40 MMT machine for nearly the same price go for it provided the spimdle properly supported by bearings and not merely a #40 grafted on an R8 spindle.

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                    • #11
                      Originally posted by JCHannum
                      once sufficient force has been applied to hold the tool, it can be removed without destroying the spindle bearings.
                      Another very strange assertion.

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                      • #12
                        Originally posted by JCHannum
                        Bridgeport initially used MT collets on their early heads. Recognizing the need for improvement, they developed the R8.
                        The early Bridgeport heads also were available in B3 tapers. B3 looks just like R8 but smaller capacity. It was standard in the C head, optional in the M. It didn't sell well. I've never seen one - I don't suppose it gripped any better than R8. 2M and 7B&S were the big sellers.

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                        • #13
                          Rant bot, What do you have against Jim?

                          You are arguing over silly preferences.

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                          • #14
                            MT taper collets, not being self releasing must be driven out to release them. Once you have used a mill so equipped, and experience the force needed to drive one out, you will understand. Bridgeport and some others did make an arrangement to jack the collet out, but not every manufacturer did. Beating on a spindle with precision bearings does not contribute to the longevity of the bearings. Tattoomike68 seems to agree with this.

                            A quick inspection of collet styles will reveal the vast majority are of the self releasing taper style. If it is indeed inferior, one must wonder why it is so universally accepted.

                            Regardless, as Forrest states, it is much more common and economical, and is the better choice of the two.
                            Jim H.

                            Comment


                            • #15
                              Originally posted by Chipslinger
                              Rant bot, What do you have against Jim?

                              You are arguing over silly preferences.
                              How so? I'm arguing the technical merits of a claim made in the thread. What's silly about that?

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