Thread locking

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Thread locking

Viewing 25 posts - 1 through 25 (of 25 total)
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  • #392682
    andrew lyner
    Participant
      @andrewlyner71257

      I have made a steady rest for my mini lathe which has a max diameter of around 60mm and it uses three long nuts and three M8 screws (phosphor bronze pads on the end). It is quite rigid enough but I want to dissuade the screws from turning whilst it's running. I guess they could tighten or un-tighten as a result of vibration.

      I am looking for a really thick grease or sticky stuff. I remember many years ago using a very soft Nylon compound for keeping magnetic tuning inductor cores in place. It would do the job fine, I think but I can't think where to obtains it.

      I wondered about a nylon grub screw. Any other well known methods for this? Perhaps M8 butterfly nuts to lock the threads?

      Cheers

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      #30691
      andrew lyner
      Participant
        @andrewlyner71257

        How to keep an M8 screw tight into an M8 nut for adjustment.

        #392685
        Bill Phinn
        Participant
          @billphinn90025

          Would a compression spring (such as found on carburettor jet screws) between nut and screw help?

          #392687
          David George 1
          Participant
            @davidgeorge1

            You can use a grub screw at 90 degrees, with a bronze slug in between the grub screw and support screw. I have used a similar thing for ball screw nuts. You assemble the parts with a tap in the support screw hole and when you rotate the tap it cutts the matching thread in to the bronze slug end. When you tighten the grub screw it dosn't damage the support screw.

            David

            #392689
            Pete Rimmer
            Participant
              @peterimmer30576

              I was going to suggest similar – a grub screw and lead pellet.

              #392690
              andrew lyner
              Participant
                @andrewlyner71257

                Cheers for the ideas.
                I fancy the spring solution for a start. I will root around in my springs drawer and see what I've got.

                Andrew

                #392703
                Chris Trice
                Participant
                  @christrice43267

                  What about a second nut on the screws you can tighten against the longer nuts? You could machine knurled brass ones as they only need to be finger tight.

                  #392706
                  Nimble
                  Participant
                    @nimble

                    In the area where the nut will rest, cross drill your 8mm bolt with approx 2mm drill insert some weedline plastic and screw the nut up, this cuts off the excess length and is similar to a nylock nut and readily adjustable.

                     

                    Nimble Neil.

                    Edited By Nimble on 24/01/2019 04:10:02

                    #392712
                    Robert Atkinson 2
                    Participant
                      @robertatkinson2

                      The compound you used before on tuning slugs was probably Rocol Kilopoise 868S (or 868GW). It seems to have been discontinued.**LINK**

                      Robert G8RPI.

                      #392713
                      not done it yet
                      Participant
                        @notdoneityet

                        Do you find your gib adjusting screws coming loose? Or any other fixings on your machine? A simple locknut seems to be adequate? So in agreement with Chris, apart from them needing a spanner, not fingers, for tightening.

                        #392829
                        Pete White
                        Participant
                          @petewhite15172

                          Third vote for keeping it simple, lock nut. smiley

                          #392841
                          ChrisH
                          Participant
                            @chrish

                            You can buy 'nylon' grub screws on the well know auction site quite cheaply, that said, you don't get that many for the price, but they seem to work.

                            #392844
                            Bazyle
                            Participant
                              @bazyle

                              Try putting a bit of fishing line down the hole. Also possibly plumbers ptfe tape.

                              #392856
                              Hopper
                              Participant
                                @hopper

                                For a lathe steady you really want positive location of all three fingers under load so I would go for some kind of positive locking mechanism such as lock nuts or pinch bolts. Otherwise, vibration and load forces plus the movement of the job across the finger tips will manage to move something. And it only takes a tiny amount of slack on those fingers to induce chatter and inaccuracies.

                                A pic of your steady would help, but without seeing it, it would seem that locknuts on the bolts where they stick out of the long nuts would be the obvious solution. Something like my own solution below:

                                dscn1078.jpg

                                Edited By Hopper on 25/01/2019 02:46:08

                                #392877
                                andrew lyner
                                Participant
                                  @andrewlyner71257

                                  @Hopper That looks a nice and meaty piece of kit. I notice it seems to be split in two halves – i guess experience told you that flexibility of use would justify any compromise on strength. My version is much the same shape but uses 8mm plate and M8 nuts. I was thinking that just making the screws 'tighter' would be more convenient than actually locking them but comments from you and other members have convicted me otherwise. I haven't room to put locking nuts 'inside' the circle so I will just use longer screws and lock nuts.

                                  Andrew

                                  #392898
                                  not done it yet
                                  Participant
                                    @notdoneityet

                                    Andrew,

                                    I don’t think anyone would try to fit locking nuts inside the circle. Takes up valuable working space.

                                    Two halves fairly well maximises the size of bar that can be accommodated while allowing easy vertical placement or removal of the worpiece ( think here of heavy commercial operations, not us hobbyists). The steady is there to support the workpiece, not force it into another position. While rigidity is a good design feature, the bar is still basically supported on only two points… If the steady points were not adjusted to the correct relationship with the workpiece and chuck, something would have to give – strain at the steady or the workpiece moving (loosening) in the chuck jaws.

                                    #392907
                                    Hopper
                                    Participant
                                      @hopper

                                      Yes, a little bit too "meaty" if anything. Cut from a piece of 1" steel plate with a plasma cutter that was not really up to the job. Never again. Took a lot of finishing work. The "flip top" adds convenience with no loss of strength apparent. Seems to be the way most commercial steadies are made in this size range.

                                      But it is much more sturdy than the standard Myford steady, which has a tendency for the slotted brass fingers to move under heavy load, such as pictured parting off 2" steel bar. Myfords puny 1/4" BSF pinch bolts on the brass fingers are no match for the 7/16" grade 8 bolts used in this design. (Specially for those of us who tend to "push" our machine tools beyond what the chaps in the drawing office ever dreamed of. laugh )

                                      #393026
                                      Howard Lewis
                                      Participant
                                        @howardlewis46836

                                        My vote would go for an adjuster capable of being held by a spanner or an Allen key, with a locknut on the outside.

                                        A member of the "If in doubt, build a brick mausoleum" brigade..

                                        (Having set the adjuster, hold to prevent rotation, and tighten lockinut. Even then, backlash in the thread is likely to produce a change of setting).

                                        Failing that +1 for fine fishing line in the hole before inserting the screwed adjuster. Locks the adjuster, and easy to replace the locking medium when it wears/fails.

                                        Howard

                                        #393039
                                        Paul Lousick
                                        Participant
                                          @paullousick59116

                                          Like all screws, there is slop in the thread and the clamping force on the bolts will push it in the outer direction. Having the nut on the outside, pulls the bolt in the same didection when it is locked-up.

                                          If on the inside, the bolt will be pushed towards the inside, making it difficult to set the distance from the part being turned.

                                          Paul.

                                          #393040
                                          Neil Lickfold
                                          Participant
                                            @neillickfold44316

                                            A drilled hole with a piece of weed wacker nylon, works very well as a mechanism for keeping a screw or a nut from loosening off. An alternate to the nylock nut. A Ø2.6mm hole is plenty of clearance for the 2.5mm line X 3 to 4 mm deep. Make the nylon about 1/2 of the thread height. It will squash up and make the screw tight to turn.

                                            #405492
                                            Harry Crowther
                                            Participant
                                              @harrycrowther39896

                                              I would use longer screws and lock nuts. I read on the Accu website that left handed screws can be used to create deliberate incompatibility to counteract the screws working loose with rotation.

                                              #405499
                                              Plasma
                                              Participant
                                                @plasma

                                                Not sure if kilopoise is unavailable but I have a large tin of it bought to use in shock absorbers for a model tank. Only used a thimble full so plenty left.

                                                It's the stuff they use to make the movement of camera threads, etc. Smooth and silky.

                                                Not sure what it would be like for the application you have in mind.

                                                Best regards Mick

                                                #405526
                                                andrew lyner
                                                Participant
                                                  @andrewlyner71257

                                                  I decided to use simple locknuts and it seems they only need be done up finger tight to keep the bronze domes in contact. The clamp works a treat; very firm and stops the pieces from wobbling even under a heavy cutting load. Once I get the three screws set right, there is no serious movement but the pads just wear a shallow groove – no problem.

                                                  PS I really could have done with some of your gunk a few years ago when I had a zoom lens that would move itself whenever it was on a slope. My heaviest grease was no use at all!.

                                                  It was cheap and I threw it out, iirc.

                                                  #405546
                                                  not done it yet
                                                  Participant
                                                    @notdoneityet

                                                    It was cheap and I threw it out, iirc.

                                                    The grease or the lens?

                                                    #405565
                                                    andrew lyner
                                                    Participant
                                                      @andrewlyner71257

                                                      I still have a large supply of lubricants but I have moved up in optical quality.

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