Bolts or studs

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Bolts or studs

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  • #499835
    BOB BLACKSHAW 1
    Participant
      @bobblackshaw1

      I've part made A A Raymans high speed marine engine at 2/3rds from the drawing. I've noticed and on other steam engines that studs and nuts are used on the cylinder and valve chest,Is this for a authentic look or some other reason .All the engines I've made I have used bolts, as for the studs are they usually cut down from bolts or is studding for 2mm any good as I brought some a few years ago and it is rubbish, or are they generally made on the lathe.

      I'm sitting at home lethargic after my operation, sorry if this is a dumb question.

      Bob

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      #27681
      BOB BLACKSHAW 1
      Participant
        @bobblackshaw1
        #499836
        JasonB
        Moderator
          @jasonb

          It's for looks as studs would have been used on the full size though as this is not based on a full size engine you can do what you like, if it were being used to power a model boat then cap heads would be more practical if it was performance and ease of maintainace you were after.

          I usually thread my own rod leaving a plain middle section unless whatever is being retained is quite thin in which case I cheat and thread it all the way

          Edited By JasonB on 06/10/2020 10:22:39

          #499840
          colin hawes
          Participant
            @colinhawes85982

            Studs are preferable in my opinion to reduce the risk of wear and other damage to critical threads when carrying out maintenance. Colin

            #499842
            BOB BLACKSHAW 1
            Participant
              @bobblackshaw1

              Thanks for the replies.

              That is a great looking traction engine you made Colin is it a working model.

              Bob

              #499846
              Howard Lewis
              Participant
                @howardlewis46836

                +1 for studs, and nuts,

                Apart from the "look", if a thread wears or strips, the stud or nut can be replaced.

                With bolts or setscrews it is the thread in the casting that would be damaged.

                Howard

                #499855
                john halfpenny
                Participant
                  @johnhalfpenny52803

                  I understood there are three(ish) practical reasons in real life:

                  No wear on the stud/casting threads, and easy replaceability of the stud.

                  No risk of bottoming out the bolt in the threaded hole.

                  Consistent nut torque, owing to the unvariable thread length engaged between stud and nut (40% being thread friction)

                  #499886
                  Tony Martyr
                  Participant
                    @tonymartyr14488

                    In traditional marine work it was easier to lock a nut on a stud, by split-pin or lock nut, than to lock a bolt which needed tab washers or wire-locking of the whole ring of bolts.

                    In more modern marine diesel work it is the need to have equal torque setting that is important and that is easier with nuts on studs.

                    Tony

                    #499974
                    Tim Stevens
                    Participant
                      @timstevens64731

                      Tony Martyr: I have seen this argument before, but I'm not sure it makes a lot of sense. Of course, you can lock a nut on the drilled stud, and of course, a bolt can come unscrewed. But what stops the stud, with its attached locked nut, twirling round and unscrewing?

                      And I'm not sure about the 'consistent torque' argument of J Halfpenny – the thread engagement is going to be the same either way, surely?

                      But then, look at a modern engine – big ends etc with no locking wire, no shakeproof nonsense, no tab washers. Just properly engineered and correctly torqued.

                      funny old world – Tim

                      #499977
                      Nigel Graham 2
                      Participant
                        @nigelgraham2

                        A nut could shake loose on a stud as it has only a small friction area additionally to the thread.

                        With a stud, there is not only the friction of the nut against the flange or cylinder-head, but probably a lot of extra friction on the stud surfaces in the through-hole and gasket, often a slightly longer thread than in the nut, and the stud is often wound down to the thread run-out.

                        #500031
                        Tim Stevens
                        Participant
                          @timstevens64731

                          Nigel 2: The flat contact area of a nut can readily be increased by using a flanged nut, especially if the flange is undercut slightly so that the outer edge bears hard, increasing the friction torque.
                          Winding a stud down to the run-out is not always a sound idea, as it tends to raise a burr around the stud, preventing the adjacent face from sitting firm, and reducing the even squash of the gasket. You can avoid the problem by counterboring the stud-hole (or countersinking) but this reduces the advantages you list for studs. Or by relying on the stud bottoming in the hole, which requires careful drilling, a bottoming tap, and rigorous cleaning of swarf, both new and in service.

                          In reality, the problems solved and created by the various options are interlinked, and there is no 'one size fits all' answer.

                          Cheers, Tim

                          #500043
                          Tim Stevens
                          Participant
                            @timstevens64731

                            PS has anyone a reason why accidental double posting happens?

                            Tim

                            #500053
                            colin hawes
                            Participant
                              @colinhawes85982

                              Bob , thanks for the comment about my traction engine model; It is a working on compressed air model and has been shown at the now discontinued Brighton model world exhibitions several times during construction. It still has some pipework to be done but I have tested the boiler to twice working pressure successfully. Colin

                              #500054
                              Vic
                              Participant
                                @vic
                                Posted by Howard Lewis on 06/10/2020 10:54:31:

                                +1 for studs, and nuts,

                                Apart from the "look", if a thread wears or strips, the stud or nut can be replaced.

                                With bolts or setscrews it is the thread in the casting that would be damaged.

                                Howard

                                Very good point Howard. wink

                                #501013
                                Gavin Carmichael
                                Participant
                                  @gavincarmichael52429

                                  I always thought the whole point of using studs was that they act as a precise locating dowel and should be either a reamed fit or very close to it to prevent lateral movement. Whilst we probably tend to think of circular cylinder covers in relation to model engineering that usually have machined locating spigots there are many instances of rectangular covers with shaft bearings in them where this precision is necessary.

                                  Additionally the plain portion should always be slightly larger in diameter than the threads to avoid thread damage when removing and replacing parts as has been mentioned in previous replies. The same argument can be used in the bolts versus set screws debate with the plain portion of the bolt acting as a locating dowel if all has been made correctly.

                                  We should also distinguish between standard bolts and fitted bolts, the latter being both dowels and very tight fits with round heads for driving into place so that there is no need to use 2 spanners.

                                  #501022
                                  colin vercoe
                                  Participant
                                    @colinvercoe57719

                                    When making studs two thread gauges are used, the end that is fixed is made slightly larger than the nut end so that it fits better into the component and locks, this allows removal of the nut without the stud coming out.

                                    #501058
                                    MadMike
                                    Participant
                                      @madmike

                                      Colin I think you are almost correct, however, and I am surprised that nobody has mentioned it, studs should ideally have two different thread pitches. The coarse one going into the casting or other major component. the end that accepts the nut should be a fine pitch thread e.g. BSW thread into a casting and BSF for the nut. This allows the stud to be secured into, say a casting and tightened down. When the nut is fitted this arrangement allows the fine thread to become the one that applies tightening torque and clamping pressure. So far so good, however when it becomes necessary to dismantle the assembly the differing thread piches will seldom operate together, which allows the nut to be removed without loosening the stud in a casting. Anybody who has ever dismantled a British motorbike will know that in 99% of cases undoing the cylinder head nuts does not loosen the studs.

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