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  • LF help selecting steel for special bolt

    Hi folks. New to the list, and new to machining in general. Finding this site chock full of great info.

    I recently purchased a used 10x18 Busy Bee B2227L chinese lathe and there are a couple of special bolts on it that are used to fasten the compound slide together that are both stripped.

    Photo here: https://imgur.com/a/1x0SS

    It is an M6x1x25 bolt with a large diameter round head, having two flat sides to keep it from turning when installed.

    I checked and the lead time for purchasing new ones is minimum 12 weeks and they want $6 for each one. I neither want to wait that long nor spend that amount on them so I thought I'd just make a couple on the lathe (I have temporarily held the CS together with some regular bolts). I initially thought I could start with an M6 bolt, but the head on a standard bolt is not big enough. I'm an uber novice at this kind of thing, though, so I don't know what kind of steel I should use to make one from scratch. I was thinking that regular mild steel would not be strong enough, so then I started thinking about using drill rod. I really don't know what to use, though, so I was wondering if you guys could suggest something. I have access to a local Metal Supermarkets for supplies, but that's about it.

    Thanks in advance.

  • #2
    The tensile strength of most steels is close to the same. Mild steel will be the same as drill rod. It'll be fine.

    Comment


    • #3
      Originally posted by Forestgnome View Post
      The tensile strength of most steels is close to the same. Mild steel will be the same as drill rod. It'll be fine.
      I agree with Forest. Most stress on the CS is vertical downward. Could you use a 1/4-28 instead of metric? Might be easier for you to find and modify to fit?

      Dan L
      “All political power comes from the barrel of a gun. The communist party must command all the guns, that way, no guns can ever be used to command the party.” (Problems of War and Strategy, Nov 6 1938, published in “Selected Works of Mao Zedong,” 1965)

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      • #4
        Originally posted by Danl View Post
        I agree with Forest. Most stress on the CS is vertical downward. Could you use a 1/4-28 instead of metric? Might be easier for you to find and modify to fit?

        Dan L
        A 1/4" bolt will definitely fit as I'm currently using a modified knock-down furniture bolt with that thread. The head on it is very thin, though, so I won't use that solution for the long run. The head on a standard 1/4" bolt is going to be 7/16 across flats IIRC, though, so it won't be big enough. The original bolt head is 14.7 mm (0.578") diameter and 11.9 mm (0.468") across the flats.

        Given what the two of you have said about tensile strength I guess I'll just go ahead and make one from some mild steel rod I have here.

        Thanks!

        Comment


        • #5
          Could you use a 1/4-28 instead of metric? Might be easier for you to find and modify to fit?
          You could do that but I suggest you keep to only one family of threads on the machine.

          As for making the bolt I suggest a two piece approach, begin with a length of metric threaded bar and a chunk of steel just to make the head.

          Comment


          • #6
            Could use stock standard imperial 1/4 x20 or possibly 5/16 x 18 carriage bolt, with appropriate grinding to fit carriage slot.

            While Canada has been officially "metrified" obtaining real metric bolts etc is still a major PITA. To get decent bolt stock 10-9 or 12-9 you have to order through Fastenall out of Indianapolis, In.
            Last edited by bob_s; 11-29-2016, 03:13 PM.

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            • #7
              look for a T-bolt and grind the head if necessary.

              http://www.mscdirect.com page 1337

              Or find a t-nut that is close and locktite or weld it to stud.

              Comment


              • #8
                Originally posted by The Artful Bodger View Post
                You could do that but I suggest you keep to only one family of threads on the machine.

                As for making the bolt I suggest a two piece approach, begin with a length of metric threaded bar and a chunk of steel just to make the head.
                Interesting. So the head could just be a small block of steel that is drilled and tapped M6? Just use some red locktite to keep them from coming apart? That would certainly be a quick and easy solution.

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                • #9
                  If it were me, I'd do a quick&dirty fix: Cut the head off the stripped bolts, drill and tap them to whatever (M6x1 if you want to use the original nuts), loctite in a length of threaded rod. Better yet, lop the head off a cap screw and use that instead of threaded rod (better type of steel).

                  Comment


                  • #10
                    Yes, something like that however you may find you need the rounded ends to the block to get it in to where it goes. In which case put two or three nuts on the thread then you can hold it in your 3 jaw and easily turn to a shape like the original.

                    Comment


                    • #11
                      Originally posted by adatesman View Post
                      If it were me, I'd do a quick&dirty fix: Cut the head off the stripped bolts, drill and tap them to whatever (M6x1 if you want to use the original nuts), loctite in a length of threaded rod. Better yet, lop the head off a cap screw and use that instead of threaded rod (better type of steel).
                      Interesting idea. The head on the original is 4mm thick, so that would mean only 4 full threads through it if I go M6x1. Enough?

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                      • #12
                        A variation on the threaded rod and block two part solution is to use some good grade 8 metric allen cap screw bolts. Then using your lathe make up thick washers with the counter bore sized cut to be a thou under the bolt's head diameter. Press in place and nothing you do will move them after that.

                        On the better cap screws you'll find that the outside has a slight straight knurl and that there is a small short shoulder just by the corner. If you make it so the smooth smaller shoulder "just" fits your counter bore you'll find that pushing them home on the slightly fatter knurled portion works like a treat. Then file the flat needed. If thickness matters and the cap screw heads are too long then make the washers so they are a closer fit and machine off the protruding portion of the heads once fitted. But to my eyes it looks like the washer will be thick enough to hold MOST of the head.

                        Using the grade 8 screws will aid in avoiding the stripping issue in the future. It's also a sign that the previous owner went all gorilla on the nuts. Don't go crazy on that stuff. And grease the thread so it doesn't gall and start that sort of stripping.

                        There's another issue at hand here too. The fact that the screws did strip out in use suggests that if you could go up a size to 8mm that it might prove worthwhile.

                        Comment


                        • #13
                          Originally posted by bob_s View Post
                          Could use stock standard imperial 1/4 x20 or possibly 5/16 x 18 carriage bolt, with appropriate grinding to fit carriage slot.

                          While Canada has been officially "metrified" obtaining real metric bolts etc is still a major PITA. To get decent bolt stock 10-9 or 12-9 you have to order through Fastenall out of Indianapolis, In.
                          Yeah, here in Edmonton, "regular" shops like canadian tire or home depot have a fairly limited selection of metric stuff. So I go to places like Edmonton Nut & Bolt, The Bolt Supply House Ltd (semi-annoying as you have to buy at least $5 to pay with anything but cash, also not a great selection of metric stuff), or Gregg Distributors (good selection of metric stuff, including threaded rod).

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                          • #14
                            Originally posted by SLeeping Dog View Post
                            Interesting idea. The head on the original is 4mm thick, so that would mean only 4 full threads through it if I go M6x1. Enough?
                            How many threads are in a typical M6x1 nut?
                            Last edited by adatesman; 11-29-2016, 04:12 PM.

                            Comment


                            • #15
                              You could start with a larger bolt with the head large enough to turn the head you have. 3/8 " or 1/2" should have a large enough head. Turn down the shank , rethread, and then turn the head to specs. I have done this often with discarded bolts. Grade 5 and 8 turn ok with hss if you slow it down a bit and use cutting oil.

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