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Cracked Rotary Table Mount - Fix it?

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  • #16

    The absolute last thing I would do is to apply any significant amount of heat as there is no way of being sure that it will not be distorted when cooled. Irrespective of whether the "weld" can even be done or not.

    Even if it is brazed, bronzed, silver-soldered or cast-iron welded etc. it may well be impossible to restore the table back to reasonable specifications/limits.

    If I recall correctly, there are "cold weld" processes that have been used to repair car engine blocks, cylinder heads etc. I am sure that some here know a lot about this from first-hand experience. There will/may be specialists in your area who do or can do this type of work.

    Putting the original bearing back in and heat-shrinking a ring onto the boss after turning it may be an option. Drilling a hole at the end of the crack - as suggested - will be a good idea.

    That must be one big mother of a rotary table!! How big and heavy is it? How do you get it on an doff the mill table? It must be one big mill as well!!!


    • #17
      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.

      That was my initial reaction too. Locktite makes some really awsome bearing epoxy for loose fits. Its not cheap though. I've got a small bottle of the stuff and it cost 23 bucks. Damn good stuff, though.

      How do you not have a way to machine the ID? Make your own if you don't have a boring head small enough for the job. Make a simple fly cutter, center the spindle over the bearing bore, then use the mill table to set the diameter of the cutter. Just make sure you return your table to the zero posistion before taking the cut!

      If it were my table (and me being a bit of freak when it comes to my tools) I'd machine down the OD and shrink fit a ring, as suggested. Then, I'd scratch the inside clean if needed (to clear a "step" or "ridge" from the crack) and install the bearing with some epoxy. A wee tiny bit left/right/forward/backward of center won't hurt anything at this point, as JC says.


      • #18
        It's Fixed!

        Thank you for all your helpful suggestions. As many suggested, brazing/Silver Soldering wold not be feasible in this case. I took JCHannum's suggestion and modified it a bit. I wasn't comfortable removing all of the gussets - I felt they were providing significant support to the bearing - so I only machined down 5/16" and made a ring out of 1/4" aluminum.

        I didn't have a boring head large enough to machine the outer diameter (it ended up being 3.752") but I did have a trepan that ended up working just fine as long as I took it slow.

        When the bearing hub was machined I carefully measured it and turned a ring out of 1/4" aluminum with an inner hole targeted at .0135 smaller (3.75" x 300F x .000012 in/in F.). I put it in the oven at 350F and after about 15 minutes, took it out and it pressed easily over the hub. The crack drew shut although it remained visible, primarily due to the dark oil that remained in it. (The crack is barely visible in the last photo at the extreme far end of the bearing.) The bearing fit snugly in the resulting hole. I reassembled the table and I can see no horizontal translation as I reverse direction.

        Thanks JC!

        By the way, I DID clean out the base before reassembling it (in case anyone was wondering).

        JC: I have no idea what caused it to crack. It had play in it when I acquired it. But, as you say, it must have been a big OUCH when it happened. Luckily it didn't affect the operation in any other way.

        Old Tiffie: The table weighs 170#. It lives on a standard Bridgeport. I get it up there usually with the help of a friend or with a hoist.

        Again, thanks to all for your excellent assistance.

        Last edited by Professor; 07-31-2008, 12:30 AM.


        • #19
          Originally posted by rotate
          Why is silver soldering not an option?
          Because silver solder and cast iron don't play nice together sometimes.


          • #20
            Nice job! Looks good. Thanks for posting pics of the steps along the way.

            I hadn't pictured the ring being near that big ... just a simple collar was what I had in mind.


            • #21
              If you haven't already I would still drill the end of the crack for precaution.
              Opportunity knocks once, temptation leans on the doorbell.....


              • #22
                Crack-stop hole

                I did drill a 1/16" hole where I imagined the crack ending. I couldn't really tell where it stopped since the shape of the structure at the visible end was complex. So I eyeballed it, drilling just past where I could see it end from the top and the bottom. Of course, the hole I made would then allow the oil to leak out so I drooled a bit of epoxy into it to plug up the leak I created.

                I suppose I should have included a picture of that, too, but forgot to shoot one when it was visible. I get involved with the process and forget to do the the documentation.



                • #23
                  All's well that ends well, and that looks like a proper repair. Good job.

                  Loctite products are excellent for their intended purpose, which are usually thread locking, bearing retention or press fit applications. They are not epoxies, but anaerobic adhesives. They produce a high shear bond, but most do not add mechanical strength. That is, Loctite would prevent the bearing from spinning or pulling out, but would do little to keep the cracked casting from spreading.
                  Jim H.


                  • #24
                    That's a very nice repair. You can probably forget about it now. Good job!