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  • POS Bridgeport spindle motor

    Well after doing countless literally hundreds of Bridgy motor shaft repairs mine has started making ominous noises as it goes thru the range.

    Anyone know anyone who does a decent repair I can't do it because the mill will be in pieces

    No joking aside I'm seriously thinking about doing a transplant and swapping the 1 1/2 HP motor for a 3 HP and getting rid of the sheave drive and fitting a single speed poly vee drive with VFD

    Got a brand new VFD but it's 440v in, 440 volt out which is no problem as the mill is 440 volt anyway.
    The rewind people will literally give me a 3HP motor just to get me back running so all it's going to take is two pulleys and a belt.

    If I fit a 1425 rev motor [ standard here for 50 Hz ] and run 1:1 that will give me 3,000 revs at 100 Hz and 430 revs at 15 Hz

    Sound OK ?
    .

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




  • #2
    my 2 cents

    I think 435 rpms is high for a low speed. Not sure what work you do with your mill, but i love the fact i can slow mine down to about 5 rpms. I have a variable speed and a VFD. Can you get a variable speed instead of the one pulley?

    Also my electrician told me to keep the minimum setting for the VFD at 5%.

    1. Your motor could be on and you would not know it if you settings go to 0

    2. The VFD will still be working, causing heat and maybe damage.

    Rob

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    • #3
      Go for it John, you'll wonder why it took you so long to go down that route. However at extremely low RPM the motors typically run out of grunt, so you may find you'll still have to sometimes take the mechanical route and swap pulleys or whatever your particular magnificent example of engineering excellence that you hold in such high esteem uses. While I have VFDs on all my machines, I've really only experienced this situation with my lathe, where I will very occasionally flick in the back gear and crank the motor RPM back up to useful output. I can certainly see the scenario with a mill however, it's just that mine is so miniscule I haven't yet needed to use the back gear on it.

      Pete

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      • #4
        Remember the Bridgy has a low range on it as well I won't be loosing this.
        .

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



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        • #5
          Do it.. but... with a 3hp motor, your POS bridgy will be a gutless wonder at less than 10hz . Bite bullet and put a 5hp motor on it, direct "in line" with the spindle. Then at 10hz and up to maybe 150hz (if your motor can take it) , you still have about 1hp.

          Yes, you can muck around and use the back gear, but....

          I run 2hp on a step belt (turned down the shaft on a POS varispeed motor - rated at 3 for less than 20 minutes). It's "ok" for most work, and I could change belts (or wind the varispeed down on my other head), but I usually can't be bothered


          Oh.. yes.. dump the sheeve and you'll gain about 30%, so maybe 3hp won't be all that bad. The reason BP went from 1 (step belt) to 1.5 (varispeed) was due to the varispeed losses, and due to a lot of customer bitching then 2, followed by a "uprate" of the 2 to 3...
          Last edited by lakeside53; 03-16-2011, 08:37 PM.

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          • #6
            Are you sure that the vari-drive bushing are OK? My bridgy come to me with a clattering head. Replacing the glue-in plastic bushings made a world of difference. The cost was about $65.
            Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
            ~Practitioner of the Electromechanical Arts~

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            • #7
              Whats so special about these bushings that you have to buy them ..
              cant you make them on the lathe .

              all the best.markj

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              • #8
                John
                Did the same with the cnc bridge about 3 years ago.
                Tooth belt drive with the slowest at 10 HZ approx 300 rpm
                and I left the back /slow gear out and instead I set it up so that
                when I put in in back gear It locked the spindle to make tool changes easy...
                just a though
                eddie
                please visit my webpage:
                http://motorworks88.webs.com/

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                • #9
                  Why not use this as an excuse to replace it..

                  Least then we will be spared the acronym POS Bridgeport... They do well what they were originally designed to do..
                  Precision takes time.

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                  • #10
                    Mill

                    John -
                    I have 2 CNC Milltronics mills with Bridgeport heads and 3 hp motors. They came with VFDs. They have 1 to 1 pulleys with a timing belt. I've been running one for over 10 years with no problems and no maintainence like there is with a variable pulley drive. They are very quiet like a step pulley and with the low range you can go down to nothing on rpm. I have made some pretty heavy cuts with mine over the years and am not lacking for power. The only diff is mine is 60 Hertz, 220 single phase. I would get rid of the sheave drive in a heartbeat. I've run about every manual Bridgeport ever made including 1,2 and 3 head hydraulic trace mills and the main thing I always hated was a clackety variable pulley drive.
                    Kansas City area

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                    • #11
                      Getting down to the correct speed for slitting saws (without stalling the spindle) can be a challenge with a VFD.

                      Phil

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                      • #12
                        At 15Hz on the VFD and in back gear it will be doing about 40 to 50 revs which is as low as I go now for the odd boring job so low speed isn't an issue.

                        I liked Toolguys reply and when I get a chance to pull this, really need a slow day, I'll go along these lines.

                        Replacing it is not going to happen , much as I hate the damn thing.
                        Too much work to get it out, at least three big machines to move first but more to the point this machine was about every conceivable extra that I would have to source for it's replacement.

                        It wasn't bought by choice but was in the right place at the right time.

                        If I had to buy one today I'd buy the step speed model and fit a VFD, the varispeed only came about as a means of having variable speed.
                        .

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



                        Comment


                        • #13
                          Originally posted by John Stevenson
                          At 15Hz on the VFD and in back gear it will be doing about 40 to 50 revs which is as low as I go now for the odd boring job so low speed isn't an issue.

                          I liked Toolguys reply and when I get a chance to pull this, really need a slow day, I'll go along these lines.

                          Replacing it is not going to happen , much as I hate the damn thing.
                          Too much work to get it out, at least three big machines to move first but more to the point this machine was about every conceivable extra that I would have to source for it's replacement.

                          It wasn't bought by choice but was in the right place at the right time.

                          If I had to buy one today I'd buy the step speed model and fit a VFD, the varispeed only came about as a means of having variable speed.
                          John

                          I fitted my Elliott mill with a VFD when I first got it, it has a 3 hp motor & stepped pulleys, I don't think I've moved the belt since first setting it up & it does everything I need. OK it doesn't do as much work as your POSB. It is a 2-speed motor and I do use the low speed sometimes, though it's only rated at 2hp on low speed. I'm sure a 5hp motor would be fine if you get the ratio right.

                          Tim

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                          • #14
                            Originally posted by aboard_epsilon
                            Whats so special about these bushings that you have to buy them ..
                            cant you make them on the lathe .

                            all the best.markj
                            They are made of a very hard plastic and less than a hundred thou thick with a somewhat thicker flange. There is also a plastic key that runs in a slot in the shaft. Both of these are glued into place while being sized by temporary precision(?) bushings, the glue and bushings being part of the kit.

                            I speculate that the plastic, hard as it is, still has a little compliance and lubricity as the sheave rumbles around the shaft. A similar bronze or lesser grade plastic bushing would rapidly deteriorate.

                            A hokey setup, someday I may contemplate an alternate arrangement, but I just replaced the bushings on my mill recently and it is working well enough.
                            Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                            ~Practitioner of the Electromechanical Arts~

                            Comment


                            • #15
                              John,

                              Many years ago I first bought the replacement bushes, but didn't like the look of them (very thin wall, no glue or instructions or internet in those days) and didn't know how to hold them in place. I since found out you can glue them in place with a dummy shaft, or something like that. Anyway, I ended up buying new pulleys from BP, they work like new and are easy to fit, and I still have the old sheaves to repair in the future if required.
                              Last edited by Peter S; 03-17-2011, 06:56 AM.

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