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Bridgeport Spindle Preload

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  • #46

    That’s wonderful news, at least so far.
    The MM207…. is the bearing I am using as a replacement. According to the bearing supply people; MM207 is a single row radial contact bearing. But that is just what they tell me and what I can determine from looking at, and measuring the bearings. Now if someone can share a document from a bearing manufacturer, that may tell us what type bearing the MM207 is, then we may all know, from a document, not just what some bearing supply person says during conversation what the bearing really is.
    I guess the other thing is… it may be that Bridgeport has, or had, more than one design and, some spindles use angular contact bearings. When we gat more info. We will be able to make a reasonable assumption. Thanks for your help.


    • #47
      The thing to remember is this,machinery mfgs will have a bearing custom made and many times leave the stock industry standard number stamped on the races.I see it everyday.The last example was Friday afternoon,Customer came in and had a common 6250-2rsc3 bearing,or so it looked as that's what was marked.I have learned to take the bearing out of the box and compare it with calipers before signing off on it.The bearing proved to have a 1" id which is slightly less common than the number on his unit.The correct number was 6205-2rsc3x1 meaning a special 1" bore.The mfg used that bearing and didn't have the race stamped to reflect the presence of a non-standard bore.

      If you look at the crossectional picture I posted you should see the profile of the angular contact bearings,notice that it isn't a symetrical crossection.If your original bearings have that crossection then they are angular contact bearings.If the crossection is symetrical then you have radial ball bearings and the point is mute.

      Understand thou that even if you have angular contact bearings they may have not been the commonly stocked type that have flush ground races which are made to be mounted in pairs.You may have single mount type which are offset ground which would explain why you have end play after replacing them.
      I think that's why you have .008" end play like you mention.

      I hope you don't take all this the wrong way,I'm only trying to help.It's one of the frustrating things about the internet,if we were nieghbors I would walk over and help you fix the darn thing and we would be done in a half hour.

      Actually,B-port is at fault here,if they had just used tapered roller bearings from the beginning we wouldn't be having this discussion

      [This message has been edited by wierdscience (edited 02-05-2006).]
      I just need one more tool,just one!


      • #48

        I appreciate the information. At this point I still only have one mission, that being to fix my Bridgeport. But, if the bearing supplies did sell me the wrong bearing, I would like conformation in the form of some documentation so can go after them with vengeance and get a refund. I am not going to ask for a refund and end up with egg all over my face because of hearsay or inaccurate information. So far, I think, just I think, the replacement bearings may be correst, and just need the preload set. But maybe we will get more info.


        • #49
          I think wierdscience has hit the nail on the head with the last posting. There are some other unique bearings in the Bridgeport much for using off the shelf stuff. The knee elevation shaft bearing in mine carries a standard Fafnir part number but has a raised hub that the "equivalent replacement" from my local bearing distributor did not. The table axis bearings were found to be different width than the basic part of their part number would suggest, also.

          In short, it looks like MM207 is not nearly enough information to get the right bearing.

          As I mentioned before, my spindle bearings are Fafnir branded, but are not original as mine are sealed. Here is a listing of letter code designations:

          The first part of the designation M207 really onlys serves to define class and inner and outer dimensions. You could get a bunch of different bearings that were M207's.

          I could break down the rest, but they define what I have as a matched pair in back to back arrangement, having a nylon ball carrier, etc. THEN...there is this FA52730 number on the end that is not described specifically anywhere. A document I happend to stumble on elsewhere on the site suggested that trailing numbers define "special stuff"...which could, indeed make them proprietary...sigh. They do have "thrust" imprinted on one side, which does suggest that they are a bearing of some sort designed for specific "side" load...something that is not the case with a common M207

          I dare say that unless you want to have to fiddle with finding out correct preload for the bearings you have(if they were radial and designed to carry a pre-load) and machining spacers to accomodate that, you may do well to find some that are sold as exact replacements. The fact that mine have different race widths and yours do not suggests they are at least different from mine.

          I was going to take pictures of my spindle parts including the bottom spindle "shield" designed to prevent contamination from the business end. It has a raised section that provides up force on the center race only. That coupled with the spacer and nut that bear only on the inner race from the other end, and the fact that my inner race is narrower than the outer, there is some pre-load or bias on the inner race, provided by the spindle "system". I think we have probably annoyed some folks enough with all the conjecture, so I won't take the pictures and post them unless someone feels they can tell what is going on by seeing them.

          In my case, I still have to figure out what direction they go in...the diagrams from NTN don't relate to what I can see with the seals pulled. Mine look the same from both sides, but I can;t really tell due to the ball carrier obscuring the view on one side.

          good luck
          Paul Carpenter
          Mapleton, IL


          • #50
            <font face="Verdana, Arial" size="2">Originally posted by pcarpenter:
            Here is a listing of letter code designations:

            It's much worse than you think. Did you note in that document, on page 4, this line -

            "DB Duplex back-to-back. Used with angular contact and precision spindle type bearing. Stamped on box only."

            That's one type of duplex bearing - used in matched pairs. Note that the bearing is NOT marked with anything to tell you that. In other words, you can't tell from looking at the numbers marked on a Timkin or Fafnir bearing if it's part of a matched pair.


            • #51
              Maybe you have the right bearings
              but you don't know what the previous owner of the machine did to the spacers.
              all the best.mark


              • #52
                Well I tried to stay out, and don't want to ad fire to the discussion, but know this.
                My records match Spindoctor with 2MM207WICRDUL being the BP replacement bearing (S)
                207 is nothing more than the SIZE of the bearing.
                The 2 M's in front are critical as they say it is an angular contact bearing. This may be spec'd as 2M, or MM or 2mm (from various Mfgs). It means Angular Contact made to ABEC-7 specs
                The WI means Counterbored outer ring
                the CR means Composition Retainer
                The DUL means (D)Double bearing mounted (preloaded) (U) for universal(DT,DB,DF) - either Tandem, or Back to Back, Or Front to Front
                and (L) for Light preload ( thats about 30 pounds! according to Barden).

                My only other comment is when you buy Spindle bearings properly...They will ALWAYS be boxed together from the factory.
                If loose or seperate...forget it
                I actually had a supply house use masking tape on two boxes to get a higher matched pair price..chuckle

                [This message has been edited by Rich Carlstedt (edited 02-05-2006).]
                Green Bay, WI


                • #53
                  Man, what a mess!

                  I finally learn that "Conrad" (a name/term I have never heard of) means a "deep groove ball bearing" Americans like using these Generic terms to confuse us (and yourselves )? I thought it must have been the name of a previously unknown manufacturer of high quality spindle bearings, including angular contact...

                  If JCD has a couple of single row radial ball bearings, albeit precision type (yes they are available, and expensive), then it is not going to work.


                  The top spindle nut on a BP may have a lock tab, but on others (eg Holke) there is no locking thing, you just do it up tight. Not adjustable! No preload adjustment!!

                  [This message has been edited by Peter S (edited 02-05-2006).]


                  • #54
                    Yes, Conrads' are great precision spindle bearings IF you have only radial loads. but thrust loads from an endmill would not be handled
                    Green Bay, WI


                    • #55
                      <font face="Verdana, Arial" size="2">Originally posted by Rich Carlstedt:
                      The 2 M's in front are critical as they say it is an angular contact bearing.</font>
                      According to the document so helpfully linked by pcarpenter, the MM means ABEC 7. The WI means angular contact, low shoulder on outer ring. And the DUL means a duplex pair, not just any double bearing.

                      Duplex pairs have to be bought as pairs, not too surprisingly.


                      • #56
                        I spent some time this afternoon looking at the correct locations of the parts of my spindle and quill through actual experimentation *and* looking at the two different manuals I have. The bearings do just "clamp" into place on the spindle as a stack of bearings and spacers in a proper order, on the spindle. This clamps only on the inner race of each bearing. Install them, tighten the nut, you are done with that part.

                        I also dropped all of the spacers and bearings into the cavity they occupy in the quill and verified that the quill "cap" screws in to a final resting place that is different than if the bearings and spacers are not in place. The quill "cap" does make contact with the outer race of the main bearings and "clamps" the stack of main bearing-outer spacer-main bearing in place inside the quill. The fact that the inner spacer is a few thousandths shorter than the outer spacer *and that the inner race of the bearing pair is narrower than the outer race* should establish some form of pre-load. In effect, the difference between inside and outside creates a pre-load merely by pulling the whole works together until the inner *and* outer spacers are both clamped in place.

                        If, the inner race on your replacement bearing was flush ground with the outer race, as described by Wierd, then the amount of pre-load created would be different than in the original implementation (assuming my spindle and spacers are "right"). Indeed, as several said before, the pre-load appears to be established by bearing and spacer dimensions (differences), so changing bearing dimensions from the original is guaranteeing failure unless you change the dimensions of the spacers to go with it. Just how to do that to meet the requirements of the bearings you have is unknown.

                        Documentation I ran into yesterday stated the obvious-- that running bearings "loose" will mean shorter life. Too much pre-load would be bad too.

                        Carefully check the inner and outer race widths on the originals and on the replacements. If they do not agree...take them back. They sold you the wrong thing and that should not cost *you*. The problem was not with varying the bearing class...but with the fact that the bearings are actually different in dimension.

                        I have gone to taking a caliper and the old bearing to the supply house for just that reason. All those extra numbers and letters on the bearing often mean something important and I have found that even the distributor doesn't pay attention to that sometimes. Good luck!
                        Paul Carpenter
                        Mapleton, IL


                        • #57
                          <font face="Verdana, Arial" size="2">Originally posted by Peter S:
                          I finally learn that "Conrad" (a name/term I have never heard of) means a "deep groove ball bearing" Americans like using these Generic terms to confuse us </font>
                          A whole mess of people don't seem to know it. "Conrad" and "deep groove" are often used as synonyms, but that's sloppy. Conrad really refers to the way the balls are loaded when the bearing is assembled. In principle you could have conrad bearings which don't have deep grooves, and deep groove bearings which aren't loaded the conrad way.

                          And it's not just an Americanism. Conrad got his American patent in 1906, but his British patent was granted three years earlier.


                          • #58
                            <font face="Verdana, Arial" size="2">Originally posted by pcarpenter:
                            The bearings do just "clamp" into place on the spindle as a stack of bearings and spacers in a proper order, on the spindle.</font>
                            Yes, all that is the most common reason why a designer specs duplex bearings in an application like this. Sock 'em up tight and you don't have to rely on the assemblers to do any fancy adjustments. The correct loads appear all by themselves.