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  • Half Nut Repair

    I don't know how to fix the Gulf leak and it looks like there's no shortage of opinions so I'll leave that to the ones that know more than I do about it.

    But I did have a job repairing half nuts on an old lathe and since that hasn't been beaten up recently I'll take whack at it.

    This is the half nuts (what's left of them) in situ on the apron of a 16" South Bend. You can only about make out where the threads once were. Leadscrew is 1-1/8-6 Acme.


    So they're mounted on the cross slide to be bored out. Not shown is the dummy for a leadscrew section to make sure of the spacing and registration. It also had a boss on it to indicate center, though in the event I was loaned a centering microscope which worked nicely. They've been indicated square and centered and a between-centers bar helps with straight.


    After boring they're also counterbored both ends to lock the new thread insert.


    ... to be continued ...
    .
    "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

  • #2
    The new thread is bronze, threaded first and turned on a mandrel to get the outside spool section and keep concentricity. Skipping a few steps including sorting out the tool bit grind for an Everede boring bar with a triangular angled (two directions) insert here are the parts ready to mate up.


    The (de-nutted) half nuts are put together with the new sleeve and lubricated liberally with Loctite sleeve mount.


    And finally when sufficiently cured, sawed apart and trimmed up to go back in service.
    .
    "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

    Comment


    • #3
      Very nice work.

      Comment


      • #4
        Nicely done! But, I have to ask, why a chemical adhesive rather than, say, solder? I'd imagine even a soft plumbing solder would be considerably stronger than the Loctite.

        Doc.
        Doc's Machine. (Probably not what you expect.)

        Comment


        • #5
          I don't have strength comparison numbers between solders and Loctite so can't comment on that directly one way or another. I do use silver solder in some applications when I think it's the best choice.

          In this case it would have taken a lot of heat because of the size of the half nut castings to be sure everything was heated evenly so the fit-up was also even. That is, the two soldering approaches would be to tin surfaces first and then heat everything and get it into position. Or to place the parts in position first and then hope to wick solder end to end and half way round. Either approach seemed problematic.

          The significant force is longitudinal which is why there are flanges on both ends. I can't imagine the rotational frictional force, even with no lubricant would be sufficent to shear the bond and rotate the threaded sleeve sections out of place. Other approaches? Sure. A secure solution for what's required? I'll stake my reputation on it and repair it if the customer ever has a problem.
          .
          "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

          Comment


          • #6
            Beautiful job Jan! The flanges on the ends were clever.

            One advantage I see to using (blue) Loctite is that if you ever wear out the half nut, you can heat it up to 350° with a heat gun and replace the nut.
            Last edited by lazlo; 06-20-2010, 12:10 PM.
            "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

            Comment


            • #7
              I think that people are too skeptical of modern ahesives. Over that area, I doubt you'd get that nut out of the casting withut damaging it even if you wanted to, without the application of heat.
              Peter - novice home machinist, modern motorcycle enthusiast.

              Denford Viceroy 280 Synchro (11 x 24)
              Herbert 0V adapted to R8 by 'Sir John'.
              Monarch 10EE 1942

              Comment


              • #8
                I would have used two screws in each half to hold them in along with the locktite. I am not comfortable using locktite or epoxy in that manner but time will tell as to how well it holds up.
                It's only ink and paper

                Comment


                • #9
                  I have the same lathe (16" South Bend) from the 1920s w/ the same worn out half-nut... I've gotten mine bored out, but the project stalled some years ago (I've got a 15" newer machine now instead of the 10" Atlas). Thanks for the kick in the pants!

                  - Bart
                  Bart Smaalders
                  http://smaalders.net/barts

                  Comment


                  • #10
                    Great looking project, Very interesting job. I especially like the way you set the thing up on your lathe. I learned a lot from the photos.
                    Thanks for sharing
                    _____________________________________________

                    I would rather have tools that I never use, than not have a tool I need.
                    Oregon Coast

                    Comment


                    • #11
                      Nice repair. I'd have glued the part together as well, but probably would have used PC-7 epoxy. I'm not knocking your use of the Loctite product- I don't know it- but I do endorse the epoxy one because I've used that and had good luck with it.

                      For those who are skeptical of epoxying parts together, remember that epoxies are not all the same. The commonly found 5 min ones are great at what they do, quickly securing parts together, but they are not what you might call an industrial adhesive. Some are better than others, and I don't have a recommendation right now of a good 5 min, but there probably is one. Of the slower varieties, I have found a few I like, and they are normally ones that don't cure to a brittle state. PC-7 does cure quite hard, but it's very strong and the bond is tenacious, as long as you leave it undisturbed to cure. A couple of the coffee table epoxies are also in my good books, and I believe that's largely because they remain slightly flexible once cured. That has to help them stay molecularly attached to materials that have a different rate of expansion with heat, and so will remain bonded for a long time. One I use now (because I can easily get it) is called Nu-Lustre-55. The usual disclaimers apply- I don't have stock in the companies, etc., and I don't receive compensation for advertising these products. I'm just a happy user.

                      I share some of the concernes of others regarding pinning or otherwise securing the parts together mechanically. One thing I've often done is drill and tap for one or more bolts, then install those at the time of epoxying. The epoxy gets squished into the bolt threads and leaves the whole assembly as one rigid piece. Even if the epoxy bond failed, the parts of the assembly would remain in alignment.
                      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                      • #12
                        Thanks!

                        Many thanks "TGTool" for the original post and others such as darryl who add helpful and useful details in their postings.

                        This is the best way for me to learn and have half a chance of achieving successful repairs of a similar nature

                        Comment


                        • #13
                          I have done these before as well, not a SB but similar lathes,
                          I'm loath to say how I did it so as not to hijack TG's very informative thread but I did use loctite and some dowel pins, roll pins actually.
                          The final job wasn't far removed from TG's

                          .
                          .

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



                          Comment


                          • #14
                            When I was in my late teens I took a job working for a company developing brushless DC motors. Old-hat today but then it was still developing technology. One of my jobs was building the rotors with rare-earth magnets around the circumference. All sizes from a 60KW traction motor with huge magnets to 100,000+rpm dentist drills. They were just fixed with epoxy on one flat surface and held up just great. They did manage to throw the magnets off one of the dentist drill motors by running it up to full speed and throwing it into full reverse on the drive circuits - it jumped a foot off the bench. Other than that I never heard of a failiure.

                            The adhesive I used for most was an oven-cured grey paste, I don't recall the manufacturer. I guess things must have developed a long way in the 20yrs since.
                            Peter - novice home machinist, modern motorcycle enthusiast.

                            Denford Viceroy 280 Synchro (11 x 24)
                            Herbert 0V adapted to R8 by 'Sir John'.
                            Monarch 10EE 1942

                            Comment


                            • #15
                              I like the boring bar. Looks like a set screw of some sort to adjust the height of the cutting tool? How to you get just the bit to advance, Is it just a standard screw and the half threaded cutting tool holder?

                              Nice job and great pics and description BTW.

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