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Cracked Rotary Table Mount - Fix it?

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  • Cracked Rotary Table Mount - Fix it?

    I have a 15" Bridgeport rotary table that exhibits some lateral play when the direction of rotation is reversed. I disassembled it and found the casting that holds the table bearing to be cracked.

    I don't have a way of supplying enough heat to braze it back together (nor a good way of remachining the diameter afterward to closely fit the bearing). Any suggestions as to how I could stabilize the crack to hold the bearing securely?

    Thanks in advance,

    Larry



  • #2
    If there is sufficient clearance, perhaps a steel ring around the outside of the bearing boss?

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    • #3
      Ouch. How did they do that?

      Mount the table on the mill, and using a boring set up bassackwards, machine the OD of the first step of the boss to remove the cast gussets and clean up the casting to some measurable diameter.

      Turn up a steel ring with an ID under the OD and shrink fit it to the boss. The home oven can be used to heat the ring sufficiently to get a significant shrink. Look up shrinks in Machinery's Hand book to determine sizing the ring.
      Jim H.

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      • #4
        A Cold solution

        After drilling the end of the crack and suitable surface preparation , layup carbon fibre and epoxy around the the outside of the central boss. Lay the tows of carbon fibre around in a complete circle around the bearing boss to use the tensile strength of the carbon to prevent the crack opening. As always YMMV

        Derek

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        • #5
          Why is silver soldering not an option?

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          • #6
            Originally posted by rotate
            Why is silver soldering not an option?
            The table still has to be raised to red heat for silver solder to work. That coupled with the fact that the crack is probably oil soaked, makes any braze type repair problematic unless proper cleaning and V-ing out of the cracked area is done.

            If the heat shrink sleeve is used, it would be a good idea to drill the bottom of the crack to help stop further propogation.
            Jim H.

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            • #7
              yeabut..... on the shrinking ring approach.... If the internal bearing surface has a small step at the crack when the machining is done, the ring will just stabilze that step. It needs to be held in alignment during the machining somehow... but I am not clear on how that could be done.

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              • #8
                Originally posted by Bruce Griffing
                yeabut..... on the shrinking ring approach.... If the internal bearing surface has a small step at the crack when the machining is done, the ring will just stabilze that step. It needs to be held in alignment during the machining somehow... but I am not clear on how that could be done.
                Install the bearing. It is a rotary table, any minor inaccuracy at that point has little, if any, effect on the outcome.
                Jim H.

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                • #9
                  Well - maybe this is just a theoretical problem, but installing the bearing may just open the crack rather than stabilize the step. If the bearing surface is slightly sprung, it is not clear to me that installing the bearing will help.

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                  • #10
                    intall the bearing with epoxy or locktite and forget about it.

                    it'll take up the slop. and you'll never stress it enough to grow that crack any more.

                    Comment


                    • #11
                      Originally posted by JCHannum
                      Ouch. How did they do that?

                      Mount the table on the mill, and using a boring set up bassackwards, machine the OD of the first step of the boss to remove the cast gussets and clean up the casting to some measurable diameter.

                      Turn up a steel ring with an ID under the OD and shrink fit it to the boss. The home oven can be used to heat the ring sufficiently to get a significant shrink. Look up shrinks in Machinery's Hand book to determine sizing the ring.

                      I think that's a superb idea. It would require some precise machine work but it should be a trouble-free repair.

                      I bought a "G" Scale (Taiwanese) model of an American Diesel freight locomotove and upon running it, discovered that all of the wheels wobbled in an annoying manner. The dealer refused to make good in the problem. When I disassembled both trucks I discovered that the plastic wheel mounts were cracked on each side where the short axles pressed in. After removing the pressed-in wheels, I machined aluminum collars sliightly undersized and pressed them onto the wheel mounts with a vise. This drew the cracks together so that the wheels ran straight after they were pressed back into the plastic axle mounts. That was about 7 years ago and the locomotive is sitll running on my layout.

                      Using a collar on the Bridgeport mount should bring the bearing hole back to original size. Once a ring is shrinked onto the machined area, it should be a permanent repair. Great idea!

                      Comment


                      • #12
                        This is not a jillion RPM jet turbine, it is at most a 1 RPM rotary table. If the bearing mount becomes deformed, it can be cleaned up with a boring bar. The worm engagement is adjustable, so the bearing mount can be somewhat off center of the original location with no effect, it need only be parallel to the table and at the proper height.

                        The entire boss could be machined away and a complete replacement made that would bolt in place from the bottom.
                        Jim H.

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                        • #13
                          Wouldn't the crack self align upon closing due to the grain structure of the iron.

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                          • #14
                            Re: Bearing stabilization

                            Originally posted by dsergison
                            intall the bearing with epoxy or locktite and forget about it.

                            it'll take up the slop. and you'll never stress it enough to grow that crack any more.
                            I have used Loctite's bearing seating compound before and it would do a fine job on this type of problem. It adheres the outer race to the pocket to prevent rotation in oversized pockets. It should stick that race firmly enough to keep the crack from opening. And, unlike epoxy, you can heat it and it will let go if you need to take the bearing out in the future.
                            Jim (KB4IVH)

                            Only fools abuse their tools.

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                            • #15
                              http://www.locknstitch.com/

                              A proven crack repair option that works, many engines etc have been saved with this one............
                              Last edited by hardtail; 07-30-2008, 08:25 PM.
                              Opportunity knocks once, temptation leans on the doorbell.....

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