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  • Tapered sheave bushings?

    Inspired by Macona's success with his 10EE, I'm doing a servo drive retrofit for a Bridgeport J-Head I bought without a motor.

    The AC brushless servo I have has a 24mm shaft, and most commonly available sheaves in the 'States have 1" bores. But MSC carries tapered 24mm 'H' and 'B' bushings, and the matching pulleys.

    I know tapered bushings are used for high-speed rotation, but is there any advantage of a tapered bushing for a machine tool spindle, where the rotation is ~ 4,000 RPM max?

    What's the difference in the tapered bushing styles ('H' and 'B')? Emerson/Browning's catalog is pretty lousy, and there's no product selection guide for the bushings...

    By the way, the reason I'm buying the pulley instead of making it is because the Browning's are ~$38 for a 7" cast iron sheave, and MSC is having their bi-weekly 25% off sale, so I can't buy the aluminum or cast iron stock for that price...
    "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

  • #2
    H1 ,P1 and Q1 are the most common sizes in the Browning line.The B size is an attempt to introduce a size series that more closely mirrors the QD style bushings that have become increasingly popular over the years.

    Browning is the only bushing with an external key which keys it into the mating bore.That is the main advantage the Browning taper bushing has over the QD style.

    Specs for the different Browning bushings can be viewed here on page 3

    http://www.emerson-ept.com/eptroot/c...20p150-157.pdf

    If all you have is a 24mm shaft an H1 is all you need,it is smaller,lighter and pulls down to a narrower assembled profile(overall width of the assembled bushing and PT componet),Plus it's cheaper and easier to find matching sheaves.

    One thing to check when you order your sheave,make sure it is balanced to your RPM requirement.Not all styles are,some are just a machined casting intended for rough service at lower speeds where balancing isn't required.

    I always recomend taper bushings over plain bores when possible,you get better shaft location,a tighter fit and less chance of creeping axially.

    One more tip,the bushing instructions say to use no lube on assembly,BS,a light coat of way oil on the shaft and sheave bore means you won't have trouble removing them later.
    I just need one more tool,just one!

    Comment


    • #3
      Originally posted by wierdscience
      If all you have is a 24mm shaft an H1 is all you need,it is smaller,lighter and pulls down to a narrower assembled profile(overall width of the assembled bushing and PT componet),Plus it's cheaper and easier to find matching sheaves.
      Thank you so much Wierd -- that's exactly what I needed!!!
      Just put the order in to MSC...
      "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

      Comment


      • #4
        By the way, because brushless servos have a flat torque profile from 0 to 3,000 RPM, I'm going to skip the drama of extending the motor shaft to match the stock shaft on the Bridgeport pancake motor. If anyone's interested in doing a similar Vari-speed conversion without modifying a stock C-face motor, here are some measurements I took today:

        The spindle pulley stack is 4 pulleys, 7.25", 6.25", 5.25", and 4.25" OD.

        I bought the Bridgeport J-Head (just the milling head) without the motor and motor pulleys, but by extrapolating the stock speeds on the Bridgeport motor plate, the motor pulley stack would be 3", 4", 5", and 6".

        Each belt section on the pulley is .625" wide. Standard A-33 V-belt.

        The aluminum head casting is .6265" thick where the motor mounts.

        There's a .125" gap between the bottom of the aluminum head casting and the top of the first spindle pulley.

        A standard NEMA 58C/145C C-face motor has a 2.125" shaft. The AC brushless servo I have has a 55 mm (2.165") shaft.

        So 2.125" (standard motor shaft length) - .6265" (alum head casting) - .125 (clearance for the spindle pulley) - [thickness of your motor plate] = how far your motor shaft will extend into the pulley chamber.

        I made a 3/4" thick motor mount, so my 55 mm motor shaft will extend .6625" into the pulley chamber. Since each pulley stack is .625" thick, that gives .0385" of tolerance. If I need more room to play with, I can drop the motor plate to as thin as 5/16".
        Last edited by lazlo; 06-25-2008, 10:39 PM.
        "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

        Comment


        • #5
          Wish I had known that,in your case the Taper-Loc bushing design would have been a better choice.The H series will work fine,just the taper-locks are a bit neater install and even more compact than the H series.

          See page 3

          http://www.dodgept.com/pdf/catalog/p..._lock_spec.pdf

          Oh and you could have ditched the vee-belt pulley on the quill and went with a poly-rib belt,but to late
          Last edited by wierdscience; 06-25-2008, 10:59 PM.
          I just need one more tool,just one!

          Comment


          • #6
            Doh. I just checked MSC, and they don't seem to carry Taper-Loc bushings. In fact, MSC doesn't appear to carry Dodge at all.

            Do the Taper-Locs need special Dodge sheaves?

            Oh and you could have ditched the vee-belt pulley on the quill and went with a poly-rib belt,but to late
            I thought about doing that, or a timing belt, but then I'd have to replace the spindle pulley stack, and the Bridgy spindle brake is buried in there.
            Last edited by lazlo; 06-25-2008, 11:06 PM.
            "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

            Comment


            • #7
              The Taper-lock sheaves to match the bushing,they are made by Dodge,Martin sprocket ,Fenner and a few others,but not by Browning.

              See it's like this-

              "Taper bushing" is a general descriptive term of the device and it's function.

              "Taper bushing "is the term which Browning uses for their product specificly,the H,P,Q bushings.

              Then there are "QD bushings" which is another type similar to the Browning,but made in a wider variety of sizes and styles.

              Both the QD and Taper bushing styles have a tapered section with a bolt flange.QD's are made by practically everybody in the PT business and follow industry standard specs.Browning taper bushings are pretty much only made by Browning and won't interchange with QD bushings.

              Now we have the "taper lock" bushing.It was originated by Fenner IIRC ,but also mfg by Dodge,TB Woods,Martin,Link Belt etc.

              It has no flange and uses setscrews or bolts which thread into the bushing/bore interface.

              Now that your thourghly confused Some tips on identifiing them.

              Browning Taper bushings usually will have for the H series two threaded holes and two clearance holes in the flange,the P and Q series will have three clearance holes.but only two threaded holes.

              The QD bushings will have three threaded and three clearance holes and will also have a stubby looking taper depending on series.One other feature will be a setscrew in the edge of the flange over the keyway.

              The taper-locks ,well they are unique,no flange and two half blank holes along with one half threaded hole.

              Of course everything revolves around numbers which are usually stamped somewhere on the product,usually on the face.

              It's a good idea to learn the diffrences,it will save you some trouble and money later.
              Last edited by wierdscience; 06-25-2008, 11:23 PM.
              I just need one more tool,just one!

              Comment


              • #8
                Originally posted by lazlo


                I thought about doing that, or a timing belt, but then I'd have to replace the spindle pulley stack, and the Bridgy spindle brake is buried in there.
                Did one already,the spindle stack is just a keyed bore,the replacement sheave with the addition of a spacer and machined up brake drum is all it takes.
                I just need one more tool,just one!

                Comment


                • #9
                  Sheaves

                  Excellent thread and posts, but could not resist the link:
                  http://en.wikipedia.org/wiki/Bringing_in_the_Sheaves

                  For those (others) that are old enough to remember it, I can still see "Ma and Pa Kettle" in one of their movies singing it - great comedy movies.
                  http://en.wikipedia.org/wiki/Ma_and_Pa_Kettle

                  Comment


                  • #10
                    Originally posted by wierdscience
                    The Taper-lock sheaves to match the bushing,they are made by Dodge,Martin sprocket ,Fenner and a few others,but not by Browning.

                    QD's are made by practically everybody in the PT business and follow industry standard specs.Browning taper bushings are pretty much only made by Browning and won't interchange with QD bushings.

                    It's a good idea to learn the diffrences,it will save you some trouble and money later.
                    Thanks again Wierd. I've got plenty of room inside the Bridgeport head for the flange, and the MSC's 25% off is pretty compelling, so I'm going to stick with the Browning H bushing.

                    Did one already,the spindle stack is just a keyed bore,the replacement sheave with the addition of a spacer and machined up brake drum is all it takes.
                    Yeah, the Bridgey brake was a lame excuse Plus you don't need a mechanical brake when you're driving the head with a servo drive or a VFD -- the DC injection braking will stop the spindle a lot faster than a mechanical brake anyway, and with an external braking resistor you can stop the mill nearly instantaneously. That should be fun with a heavy milling cutter in the spindle

                    So is a Poly-V a lot smoother than a conventional V-belt or a timing belt? I know there's a bit of torque cogging that goes on with a V-Belt as it contracts and expands around the pulley diameter, which is the reason for cogged V-Belts like the Gates PowerTwist belts ...
                    Last edited by lazlo; 06-26-2008, 09:57 AM.
                    "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                    Comment


                    • #11
                      Vee belts get lumpy for starters,they also are less efficent than poly-vee even if it's only a couple percent.

                      Where they pay off is vibration and noise.Poly-vees run smooth,much smoother than vee's.There is a SFPM limit on vee belts also,that is one reason the automotive industry began using them.

                      Plus using the Stevenson-O-matic machining method you can make your own sheaves quick.
                      I just need one more tool,just one!

                      Comment


                      • #12
                        Originally posted by wierdscience
                        Where they pay off is vibration and noise.Poly-vees run smooth,much smoother than vee's.

                        Plus using the Stevenson-O-matic machining method you can make your own sheaves quick.
                        OK, you shamed me into the Poly-V's Wierd. I actually have the Kennametal 40° TopNotch inserts, so turning Poly-V sheaves is no problem.

                        Is there a Poly-V calculator somewhere that I can calculate how wide a belt/sheave I need? My servo is 1.5 KW (just over 2 horsepower) in continuous duty, and servos run at 150% in intermittent duty, so I'm guessing I should make a sheave wide enough for 2.25KW = 3 horsepower.
                        "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                        Comment


                        • #13
                          Need to know max revs and smallest pulley size, plus what section J or L [ J would be best ]

                          Forget it just read 3" and 4,000

                          Service factor = 0.89

                          So number of ribs = power over service factor 3 / 0.89 = 3.37

                          So 4 grooves will handle this.

                          .
                          .

                          Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



                          Comment


                          • #14
                            Originally posted by John Stevenson
                            Forget it just read 3" and 4,000
                            Service factor = 0.89

                            So number of ribs = power over service factor 3 / 0.89 = 3.37
                            So 4 grooves will handle this.
                            Thanks John! A servo is designed/rated to run at ~ 3x rated torque intermittent, so wouldn't the Service Factor be ~ 1.5? A standard NEMA motor (not your typical Chicom treadmill motor) has a service factor of 1.0...

                            Also, don't you need to factor horsepower and especially torque into the belt width? My servo is 1.5 Kw, and 16 Ft/lbs (21.6 Nm) maximum torque (!), so I would think you'd need a wide Poly-V to keep it from slipping under worse-case conditions?
                            Last edited by lazlo; 06-27-2008, 10:58 AM.
                            "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                            Comment


                            • #15
                              I dug around in my junk box and found an old set of pulleys that came off of a 1.5hp table saw. It was setup for a 1 to 1 drive and the pulley was a six groove approximately 15mm wide (no idea where the original belt is). If you look at page 1028 in the online mcmaster catalog, they list a 10 groove j section belt and bushing style pulleys that should easily handle the load. Also, from looking at the way they were made, they should be pretty simple to make since you have the inserts.

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