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Tapered sheave bushings?

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  • #16
    Originally posted by MickeyD
    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.
    Thanks Mike! The 8- and 10-groove V-belts are only $15 each, they're made of cast iron, and they take the low-profile TaperLoc bushing that Wierd recommended. I'm going to order those from McMaster.

    Wierd: if I'm reading the McMaster catalog correctly, the TaperLoc bushings handle a range of bore sizes? McMaster's part number for the bushing specifies 1/2 - 1" bore???

    You guys are a bad influence -- now I'm going to have to take the head apart to get the spindle pulley stack off...
    "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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    • #17
      Ah, I found the answer to my first question about John's numbers: according to Machinery's Handbook, you need to calculate service factor times horsepower -- that makes a lot more sense.

      I found the formula to calculate the horsepower ratings of Poly-V belts on 2419 of the 27th Machinery's Handbook. What you do is calculate the horsepower rating for a single V, and then pick the number of V's to accommodate the horsepower.

      The problem is that I'm getting 1.6 HP per rib, which doesn't sound right. Hmmm....
      "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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      • #18
        I am pretty fond of the Fenner Power Twist belts for anything that sits under tension. You would be surprised how much vibration is induces by an egg shaped traditonal v-belt from forming to the shape of the pulleys around which they are wrapped. I am sure, however, that there is probably a little "give" in a link belt like that though.

        By all means don't give up the brake even if your DC controller lets you do braking. I don't use it much for stopping the mill....I am not in a hurry and there's enough driveline friction in the variable speed heads I am used to that the spindle stops quickly. On the other hand, I don't know how you would ever tighten a drawbar properly without the brake (short of building a power drabar with an impact wrench)

        Paul
        Paul Carpenter
        Mapleton, IL

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        • #19
          Originally posted by lazlo
          Wierd: if I'm reading the McMaster catalog correctly, the TaperLoc bushings handle a range of bore sizes? McMaster's part number for the bushing specifies 1/2 - 1" bore?
          That's one of those things where you call them up ,give them the part number and they ask you what bore size you want in that range,saves catalog space.
          I just need one more tool,just one!

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          • #20
            Robert,
            The service factor came out the table in the Polyvee book and relates to the belt, not the motor.

            .
            .

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



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            • #21
              Originally posted by John Stevenson
              Robert,
              The service factor came out the table in the Polyvee book and relates to the belt, not the motor.
              Now I'm thoroughly confused Machinery's Handbook shows a table of "Design Horsepower" which is Horsepower x Service Factor.

              Does your Poly-V book indicate how many ribs would be needed for 3 horsepower? I'm guessing somewhere in the 8 to 10 rib range, since Mike's bandsaw had 6 ribs for 1.5 HP.

              I'm going to make a little spreadsheet of the Machinery's Handbook Poly-V formulas. The J-Belt horsepower formula has 13 terms in it
              "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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              • #22
                By the way John, I'd rather err on the side of too many ribs in the V-belt, because I want virtually no slip.

                The biggest reason I went with a servo drive is because I've finally collected all the parts to make the servo gear hobber I've been mentioning for awhile. Rather than have a rotary encoder on an outrigger like you did on the Victoria, I'm going to pull the mill spindle quadrature off the servo controller into the gear hobber divider circuit.
                "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                • #23
                  A bunch of searching turned up several belt calculators, but none that calculated Poly-V belts. To complicate matters, "Poly-V" is apparently someone's trademark, so the various vendors call them different names. Machinery's Handbook calls them "V-Ribbed" belts.

                  I called Gates yesterday, and they turned me on to their "DesignFlex" software, which calculates a custom drive configuration given the physical drive requirements (horsepower/torque, service factor, drive ratio, desired RPM's, optimal center distance, ...). The software is a free download, but you have to register.

                  The software is limited on drive motors, so I specified a 2 HP, NEMA 146 motor with 3450 RPM max. That's 450 RPM faster than my servo is rated, so I modified the desired top-end RPM by 3450/3000 to get the correct final RPM for the Bridgport head: 4,000 RPM. The servo is 2HP continuous, 3 HP intermittent, so I specified a service factor of 1.5. The center-to-center distance on the Bridgeport pulley stacks is 8.25" +/- ~ 10% (the amount you can wiggle the motor plate for belt tension).

                  In any event, after plugging the data for my servo into the Gate's calculator, they come up with a recommendation for a 240J6 belt/sheave, which is a 6 ribbed, J cross-section belt. Notice that they give you a complete parts list of belt, sheaves and bushings, and even tell you the "optimal" belt tension for a new belt and a used belt. Very nice!

                  Thanks Wierd, John and Mike!

                  Mike -- can I come by this afternoon and take a look at those Poly-V sheaves you have? There's beer in it for you

                  Last edited by lazlo; 06-28-2008, 11:45 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


                  • #24
                    I've put on my asbestos suit in case of a serious flaming but I have to ask a retarded question

                    What on earth is a tapered sheave bushing (or any kind of sheave bushing) and what is it for?

                    --Cameron

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                    • #25
                      I didn't know what they were either Cameron -- it's literally a tapered plug with a locking taper that cinches up the sheave onto the motor shaft. Apparently a tapered sheave has a superior fit and less vibration that a conventional straight bore sheave:

                      "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                      • #26
                        True story about poly vee belts.

                        I originally got involved with these working on some conversions for some Taiwanese wood lathes. They had double expanding pulleys to get the speed down for large bowl turning but the drives slipped like crazy so I looked at fitting a 4 stage poly vee drive before the last expanding pulley. This way it was possible to get from 80 up to 4,500 for small work.
                        I contacted the main people in the UK at the time TBA belting and got a design handbook.
                        Brilliant book gives centre distances, power belt load per groove, ratio's etc but the one thing I wanted was missing.
                        As this lathe had fixed centres, I knew the belt length and the centre distance and also knew one set of pulleys but I had to have the other set exact as I had only the tiniest amount of adjustment with an idler roller.

                        The book gave everything but so i rang them up and explained the problem but couldn't get it over to them what i wanted. I knew what I wanted and it meant transposing the formula for the belt length knowing centre distance and both pulleys but I'm crap at algebra .

                        Rang this professor up I know but he was on holiday so I wished I had payed more attention when I was at school.

                        School ????

                        Right laid it all out on a sheet of paper and headed it as follows.

                        " I was born in 1948, the year Aneurin Beven promised the people of the United Kingdom we would be looked after from the cradle to the grave [ a remark about our health service ] so seeing as I never managed to understand algebra when I was at your school from 1959 until 1964 could you please transpose the following formula to give me the values for d' and D'"

                        This was faxed off to my old school.
                        Following day came back the two formula's with the note.
                        "Pay more attention in class !! "

                        .
                        .

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



                        Comment


                        • #27
                          A good fit

                          Originally posted by ckelloug
                          I've put on my asbestos suit in case of a serious flaming but I have to ask a retarded question

                          What on earth is a tapered sheave bushing (or any kind of sheave bushing) and what is it for?

                          --Cameron
                          Hi Cameron.

                          Much as lazlo says.

                          It is really just a variation on the principles of the "ER" series of collets where the "collet" is "pushed" into engagement where-as the "C" and MT (and the like) collets are "pulled" into engagement. The same rules apply to the taper bushing as regards accuracy of concentricity, taper and "round/parallel" as does the ER (or any) collets.

                          There is not or should not be any radial clearances (on diameters) or "slack/back-lash" as might be the case with key-ways either.

                          They are a very elegant and practical solution to positive location/alignment and drive.

                          There are a lot of variations of them in use in many fields.

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                          • #28
                            Originally posted by John Stevenson
                            I contacted the main people in the UK at the time TBA belting and got a design handbook.
                            Brilliant book gives centre distances, power belt load per groove, ratio's etc but the one thing I wanted was missing.
                            One of the members here (I don't know if he wants me to use his name ) pointed me to the EPT/Browning Poly-V design handbook, and a hour of reading and some simple calculations answered several questions.

                            Originally posted by lazlo
                            I found the formula to calculate the horsepower ratings of Poly-V belts on 2419 of the 27th Machinery's Handbook. What you do is calculate the horsepower rating for a single V, and then pick the number of V's to accommodate the horsepower.

                            The problem is that I'm getting 1.6 HP per rib, which doesn't sound right.
                            So it turns out that my calculation was correct. Poly-V belts are fascinating little beasties!

                            It turns out that the horsepower rating on a Poly-V belt is proportional to the belt friction. You can create that friction either with a wide belt (more V's), or with a bigger pulley, which has more belt in contact with the sheave.

                            When I calculated the 1.6 HP per rib, I was using the 7.25" of the stock Bridgeport conventional V-Belt sheave. That's a giant sheave in the Poly-V world.

                            So when I was running the Gates DesignPro calculator, I kept trying to force the sheave diameter to what you'd expect in a conventional V-Belt (5 - 7"), and the software kept telling me to use a 3 or 4 ribbed V-Belt. 3 V-Ribs on a 6" sheave at ~ 1 HP per rib = 3 HP, which is the servo rating at the 150% (intermittent) rating.

                            So 4 ribs with a 6" pulley has the same horsepower rating as 6 ribs with a 3" pulley. The friction generated isn't linear, so you either have to use Gates/Browning's tables, or calculate the horsepower rating according to the Machinery's Handbook formula.

                            Now here's where things get interesting: this is a servo retrofit, and as Macona pointed out on his 10EE retrofit, servos have full torque all the way down to 0 RPM. Poly-V belts are really intended for high speed operation, since a lot of the belt friction (and therefore, horsepower rating) is from centrifugal tension. In other words, the motor is pulling the belt around the sheaves at 3,00 feet/min, which generates an immense amount of friction.

                            At low speeds, say 250 RPM for a big flycutter or facemill, the centrifugal friction drops way off, so there are exception tables with minimum sheave sizes for low RPM. For a 3 HP motor at 575 RPM, Gates indicates a minimum sheave size of 4.8" on the driver sheave.

                            So for a machine tool (lathe or mill), you really want the largest Poly-V you can fit into the spindle. Plug that sheave size into the Machinery's Handbook formula, or look it up in the Gates/Browning tables, or run DesignPro, and it will recommend a pretty narrow Poly-V belt (3 or 4 sheaves).

                            The other upside to the big sheave, narrow Poly-V belt configuration is that the bigger the sheave, the less belt tension required, so it's a lot less stress on the motor and pulley stack bearings. And the biggest upside: the noise of the Poly-V system (which is really quiet to begin with) is inversely proportional to the sheave size, so the bigger sheaves are quieter.

                            So I ended up with a configuration of a 5.3" driven sheave, a 4.0" driven sheave, and a 4-ribbed Poly-V belt. Gates DesignPro tells me that system is rated for 4.3 HP, which is healthy safety factor over the servo's max output.

                            One last comment: the Poly-V sheaves are surprisingly cheap. The powdered metal Gates sheaves are ~ $30 for a 5" sheave at McMaster, and E.B. Atmus in Springfield, MA has them for at least 15% cheaper than McMaster:

                            http://www.ebatmus.com/index.html

                            If this is painfully boring, someone say so and I'll just post some pictures when I'm finished with the servo retrofit
                            Last edited by lazlo; 06-29-2008, 10:25 PM.
                            "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                            • #29
                              The scary thing is how interesting this is. I had never worked through the calculations before so I had no idea how efficient these belts were, all I had was seat of the pants experience with them.. Someday I need to change the belts out on my Colchester lathe, so if I can find a belt that is close to the right size, I will switch it from tripple v belts to a single poly belt. That could be an interesting upgrade...

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                              • #30
                                Originally posted by lazlo
                                If this is painfully boring, someone say so and I'll just post some pictures when I'm finished with the servo retrofit
                                On the contrary, all this is very interesting. Does that mean you won't post pictures?
                                .
                                "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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