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  • Bridgeport Spindle Preload

    Help! I Just replaced the spindle bearings in my Bridgeport Mill, what a job. When I inquired, at my local bearing store, about replacement ABEC X bearings the guy said “unknownâ€‌, so he made an inquiry to Bridgeport. They started that the ABEC Spindle bearings for this machine are proprietary and manufactured special for The Bridgeport Co only.
    I decided upon ABEX 8, thinking why spend the extra $ for my home shop, and installed the bearings. Based on a guess, and some hear say, I used the same preload spacers and put the spindle back together.
    . When milling, at he beginning and end of the cuts I get chatter. Not a Good situation as no chatter existed with the old bearings. I think I don’t have enough preload.
    What should the preload be, and how do I get the bearings off the spindle shaft without damage to the bearings?
    If someone has had experience, please be so kind as to take a few minutes and respond to this plea for help.
    Thanks

  • #2
    The preload is set by the dimensions of the bearings and the spacers. If your replacements don't match the originals EXACTLY, your preload will be off.

    ------------------
    Leigh W3NLB
    Leigh
    The entire content of this post is copyright by, and is the sole property of, the author. No assignment
    of title nor right of publication shall ensue from presentation of this material on any computer site.

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    • #3
      Based on a guess, and some hear say, I used the same preload spacers and put the spindle back together.


      thats why Bridgeport used to do exchange spindles.........
      not sure maybe your supposed to surface grind the spacers to get it right.

      think you have to work out which one of the spacers to grind to take up the slack.
      but don't go doing it till someone here has verified what i have said ..im only guessing
      all the best.mark

      [This message has been edited by aboard_epsilon (edited 01-31-2006).]

      [This message has been edited by aboard_epsilon (edited 01-31-2006).]

      [This message has been edited by aboard_epsilon (edited 01-31-2006).]

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      • #4
        Never gotten into a Bridgeport spindle. I have, however, designed precision spindles (which is why I have no great desire to get into a Bridgeport spindle).

        The ABEC (Annular Bearing Engineering Committee of the AFBMA) standards are tolerances on certain dimensions of the individual bearing parts - the inner and outer races and the balls. Radial and axial runout of the raceway with respect to the ring ID or OD or side face, etc. They have little to do with the assembled bearing. Most specifically, the ABEC class number says nothing about the internal clearances of the bearing (ie, the "play") - those are specified by the spindle designer. The bearing manufacturer selects bearing components so that his assembled bearings will met the designer's specifications.

        When you buy a replacement bearing from the machine manufacturer (not the bearing manufacturer!), you will automatically get one with the correct tolerances, if the company is on the stick (not all of them are). The clearances are important because (particularly if the designer has used a duplex pair arrangement, as he almost certainly has in a precision spindle) when the bearings are tightened down in their housings, the proper preloads will happen automatically. This is why you can't get just any old bearings from the local Bearings 'R Us and expect them to work like the factory ones. Duplex pairs are designed to be clamped tightly together, with the little arrows marked on the raceways lined up. Rather than clamping them together, the designer may have put in spacers. These spacers are ground to precise lengths, again so that the correct preloads will happen automatically when the bearing are socked down in place. Duplex pairs are matched by the bearing manufacturer, and can't be mixed up with other pairs.

        All this is why I don't recommend that people buy used mills which "only need new spindle bearings" and why I suggest that they keep their old bearings until they actually fall apart. The standard backyard restorer thinks that he might as well replace the bearings while he has the thing apart for painting. It's usually a bad move.

        Unless the data has been published somewhere, there is no way to determine what the designer thought the bearing loads should be except possibly by measuring some dimensions on a good set of bearings and on a properly assembled spindle, something few of us are equipped to do.

        All of which is little help in the present situation. What is the condition of the old bearings? If this happened to be my mill, and if the old bearings weren't totally shot, I'd put them back in.


        _______________

        "if the designer has used a duplex pair arrangement, as he almost certainly has in a precision spindle" - I probably shouldn't say that as it's easy to misinterpret. Duplex pairs are a good way to do spindles but they're not the only way. They're big in ball bearing applications. Lower speed but higher load applications may be better served by tapered rollers, and the principles of duplex bearing design don't hold so well for roller bearings. I emphasize that I don't know what arrangement Bridgeport spindles use(d).


        [This message has been edited by sauer38h (edited 02-01-2006).]

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        • #5
          I make belting at a bearing supply store. My Bridgeport needed spindle bearings. They had a set on the shelf as stock. Been about 6-7 years ago, paid $250 for them, they said normal price was $400. Try asking around at another supply house. I still have the old ones if you need numbers.
          mark costello-Low speed steel

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          • #6
            This is very very bad news. Hopefully, as the day goes on, things will get better.

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            • #7
              JCD,

              Did the new bearings come as a pair? ie, maybe in individual boxes, but sealed together so there is no doubt they are a pair.

              I have replaced one BP and one clone spindle bearings, I purchased the replacements from RHP (original supplier to BP UK), they have worked fine.

              But I stress that they were supplied as a paired package of bearings.

              Also, there are several ways you can install these bearings (back to back, face to face, tandem)....do you have them "back to back"?

              Back to back has the largest diameter of the taper on the outer race facing outwards. There should be diagrams showing this on the Fafnir website.

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              • #8
                The spindle bearings are Conrad type (single row radial) and after doing a considerable amount of research, including conformation from Bridgeport, Conrad type bearings are the correct bearings for this spindle.
                The problem now boils down to just one thing: ignorance on my part, or just not knowing what the correct preload is for the application. As far as Bridgeport is concerned the bearing preload in propriety, and they just aren’t telling. The field service person I talked with doesn’t know, as he doesn’t rebuild spindles “in the fieldâ€‌.
                I did find preloading specification from the bearing manufacturer, but the preload is in pounds of force. I need a dimension in inches, or more precisely, parts of an inch so that I can adjust the preload. I sure heed help from someone.

                Comment


                • #9
                  There is a person on the (ahem) Practical Machinist board with a cool screen name of Mr. Bridgeport, wonder if he would know? Also Yahoo groups has a Bridgeport forum. Flame suit on and Scotty beam me up.
                  mark costello-Low speed steel

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                  • #10
                    Sorry but I dont know, but if you visit my yahoo group http://groups.yahoo.com/group/bridgeport_mill there are some machine rebuilders there who may help. JRouche

                    I just did a search at the bridgeport site for "bearing preload" and there was quite a few results, maybe something already posted to help you...

                    [This message has been edited by JRouche (edited 02-01-2006).]
                    My old yahoo group. Bridgeport Mill Group

                    https://groups.yahoo.com/neo/groups/...port_mill/info

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                    • #11
                      I replaced my Bridgeport bearings with 2 single bearings rather than a matched pair - and I used Abec 7 not 9. The result - absolutely no problems what so ever in the home workshop. IMHO there's more bulls**t about bearings and the pursuit of unnecessary precision in the home workshop than probably any other area. I was quite willing to have to regrind the spacers but it wasn't needed.
                      Think of it this way. The machine is probably 20-30 years old, the bearings have probably been running way out of original specification for the whole of your ownership. "Chasing the dragon" of the last tenth of a thou of precison will quadruple the cost and 99 times out of 100 you won't notice it. That however assumes that machines are for using, not just repainting and admiring - and don't we all know that's some people's angle.

                      Charles

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                      • #12
                        Charles, I will have to agree; sometimes we are more than willing to spend Megabucks on parts that may last long after our lifetimes.

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                        • #13
                          I have taken the spindles out of three B-port mills and replaced the bearings with Tinken precision tapered roller bearings for $150 less than the angular contact ball units.
                          They work very well,will run just as fast,carry four times the load and offer the same runout.

                          The only modification required is to either machine down the spacers or make new ones.Either way the ones I did required about .100" to be removed.

                          Spacers aren't rocket science either,machine the OD,ID and part off .020" over length.You will need access to a surface grinder,but that's no biggy either.Grind parallel,rotate 90*dust off at same setting,rotate another 90* dust off at same setting grind both spacers at the same time they will be perfect.
                          I just need one more tool,just one!

                          Comment


                          • #14
                            JCD emailed me with an appeal to discuss his his problem. I thought he was being well advised here so I only followed the discussion. However, since he asked me to weigh in:

                            My Email text to JCD follows:

                            A wide variety of periodic phenomina have been refered to as "chatter". Here's is the procedure for determining whether an angular contact bearing pair has the correct preload.

                            Mount a mag base on the extended quill.near the retainer nut. Mount a 0.0001" dial test indicator to the mag base so the contact is registering motion of the spindle collet taper. Rotete the spindle by hand to see if the collet taper runs within 0.0003". If it's OK accept it and move on.

                            Move the indicator and install your largest clunkiest end mill or shell mill adaptor. Restore the indicator to register the OD of the spindle. Draw a circle around the contact point with a felt tip pen for repeatable positioning. Shake the spindle by hand strongly attempting to force the spindle sideways. You will see a few tenths of deflection but when you relax the spindle should go back to zero (if the circle is centered under the contact point). Move the indicator so it registers on the spindle end and repeat, shaking vertically. If the indicator registers any free motion at all there is something seriously wrong.

                            Remove the mag base and indicator. Stick a small meat thermometer to the lower end of the quill with modeling clay. Set the spindle to high speed and run the spindle full out for a half hour. The spindle should warm up about 10 to 20 degrees F as measured by the thermometer. This is similar to the final check in the most sensitive and accurate machine tool spindles: the temperature control is disabled and the machine run at high speed for some time while the observer looks for a range of temperature rise. If the spindle does not warm up that's in indication of insufficient preload. If the spindle warms up over 20 degrees at thermal equalibrium the preload may be a bit too snug. Over 30 degrees definitely too snug.

                            Use a screwdriver as a stethoscope to listen to the bearings: you should hear a soft whir. If you hear any tickings or grumbling you have a problem with dirty assembly.

                            As for the chatter you describe: (you don't mention material, cutter details, machine settings, spindle extension etc) it may be an artifact of spindle endplay or it may be the behavior of a properly set preload. The old bearings may have loosened up enough to damp out this phenomenon whereas the new because they are rigid may not. The same phenomena may have different interpretations depending on context.

                            Spindle work is tricky. It's not like changing out wheel bearings because you have to be so careful of cleanliness, parts handling, deburring withhout affecting geometery and dimension, installing the bearings so the burnish marks align and all the rest. I always shudder when people have a "chatter" problem who blithly blame it on "sloppy" spindle bearings. There are so many more quite simple causes for the problem. Few seem willing to conduct a few simple diagnostic tests before tearing into the spindle. On the strength of an assumption or what "some guy" told them, a naife will take apart a precision machine tool spindle (often using rough methods) and only then ask questions and get concerned about bearing Classes. of fit, suitable sources etc.

                            I'm not suggesting the inexperienced can't do good spindle work. I am suggesting they often bite off more than they can chew thanks to little or no research, blithe assunptions, giving credence to the advice of someone who means well but is ignorant, inadequate tools and equipment, and lack of the excrutiating care necessary for spindle work.

                            The circularity of a spindle axis is about 20 times more accurate than that necessary in an asle bearing and 10 times more accurate in an induction motor bearing. The class of workmanship and the cleanliness and ove- the-top care employed in spindle work has to reflect this accuracy.

                            End of text. Adding JCD write: "The spindle bearings are Conrad type (single row radial) and after doing a considerable amount of research, including conformation from Bridgeport, Conrad type bearings are the correct bearings for this spindle." Bridgeport spindle bearings are NOT conrad type but an angualar contact matched pair.

                            If you installed conrad (actually "radial) bearings (this term refers to non-filling groove ball bearings whose inner race is eccentrically displaced for filling: conrad - concentric radial) there is your problem. If you have indeed installed radial bearings it will be immediarely apparent in the axial shake test. You'll see anywhere from 0.005 to 0.020" end play when there should be none.

                            Radial (conrad) bearings can be made to high class numbers and their accuracy and circularity can be held to as close a tolerence as the finest of angular contact bearings. They are made with built-in internal clearance and so have no intrinsic control over axial motion. They are commonly used as "float" bearings to support the driven end of the spindle -indeed there is a raidal or double row flow bearing at the spline end of your spindle. It's not uncommon for a radial bearing to have 0.0008" assenbled radial clearance and 0.012 axial motion. Thus they cannot be used in the business end of the spindle. I cannot imagine anyone knowledgeable at Bridgeport using "conrad" is connection with spindle bearings.

                            I strongly suggest you look up "angular contact bearings" and clarify some concepts.

                            http://www.ntnamerica.com/Knowledge/...ng_AngCont.htm

                            Look at the ourter race of your old bearings. If one side of the outer race is much thinner that the other (look at the cross sections in the link) that's a sure identifier for an angular contact bearing.

                            The identifying number for angular contact bearings suitable for spindles is a long affair with many designators. Each designator has to be de-coded to determine if you have a correct cross match with the original spindle bearings.

                            Many bearing manufacturers offer off-the-shelf precision angular contact bearings suitable for immediate installation in a turret mill spindle. There's no point to paying a $150 premium for the manufacturer to run the same set of bearings in and out of his inventory if you could purchase from the local bearing supply house and get quicker service.

                            JCD, without looking at the whole bearing and its number its hard to say what you have but when you said "conrad" it set off all kinds of alarm bells. If have indeed installed plain radial ball bearing in your BP spindle you've been led to a bad conclusion and your bearing supplier needs to have his a$$ kicked - very hard. There is no remedy but to obtain the correct bearings and install them.

                            Edited to insert the word "radial" as appriate. It kept slipping away from me last night.

                            [This message has been edited by Forrest Addy (edited 02-02-2006).]

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                            • #15
                              <font face="Verdana, Arial" size="2">Originally posted by Forrest Addy:
                              They are made with built-in internal clearance and so have no intrinsic control over axial motion. They are commonly used as "float" bearings to support the driven end of the spindle -indeed there is a conrad or double row flow bearing at the spline end of your spindle. It's not uncommon for a conrad bearing to have 0.0008" assenbled radial clearance and 0.012 axial motion. Thus they cannot be used in the business end to the spindle.</font>
                              That's not actually so, if the luxury of pairs of bearings is available. Conrad bearings with even greater clearances start to have the axial load capacity of angular contact bearings, and the excess play can be taken out by loading them axially - which is what the "duplex" arrangement is all about. But so as to avoid muddying the waters, if the Bridgeport spindle doesn't use duplex pairs, I'll say no more about them.

                              [This message has been edited by sauer38h (edited 02-02-2006).]

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