9 Replies Latest reply on Jun 4, 2018 2:29 PM by Dan Golthing

    Thread modeling

    Matt Thomas

      Ello all:)

       

      I have a question about thread modeling and the properties found in SW.

       

      I am currently finding a book called the machinsts handbook or something like that because i have never seen how threads are made.

       

      ok, in my book, we are making a cable tension device. It has a hook on each side and then you turn them in to tighten attached cables.

       

      I get to the very end where i need to add the threads, it all makes great sense until the revolutions part. Book wants me to use 11 revs for the spiral helix. I type in 7 and i notice it ias about 3/4ths the way to the back side of the hole. Interesting i think. so i try 11, its flush. Ok, so my question is, does the spiral have to be exactly the same length as the hole that is to be threaded or can the spiral jut out a revolution or two from the back side of the hole? if that is bad pratice, how does one find the exact amount of revs is needed to thread a part? Or do we not thread parts anymore for drawings and just notate them?

       

      thanks

        • Re: Thread modeling
          Dennis Dohogne

          Matt Thomas wrote:

           

          Ello all:)

           

          I have a question about thread modeling and the properties found in SW.

           

          I am currently finding a book called the machinsts handbook or something like that because i have never seen how threads are made.

           

          ok, in my book, we are making a cable tension device. It has a hook on each side and then you turn them in to tighten attached cables.

           

          I get to the very end where i need to add the threads, it all makes great sense until the revolutions part. Book wants me to use 11 revs for the spiral helix. I type in 7 and i notice it ias about 3/4ths the way to the back side of the hole. Interesting i think. so i try 11, its flush. Ok, so my question is, does the spiral have to be exactly the same length as the hole that is to be threaded or can the spiral jut out a revolution or two from the back side of the hole? if that is bad pratice, how does one find the exact amount of revs is needed to thread a part? Or do we not thread parts anymore for drawings and just notate them?

           

          thanks

          Matt,

          It is good that you are referring to the Machinist Handbook.  That a resource we commonly tell people to get their hands on.  But don't just refer to it, read the section on threads so that you understand the terms.  Metric screws are identified by their major diameter and pitch, i.e., an M6X1.0 has a major (outside) diameter of 6mm and the thread pitch is 1.0mm.  That is how far the screw advances on one complete revolution.  It is also the distance between identical points on adjacent threads, such as the peak-peak.  For inch size threads such as 1/4-20 the major diameter is 1/4" (.250") and there are 20 threads per inch (TPI).  All that said, if you want to model threads SWX has some built-in options so read up on that in the Help.  If you really want to model the threads then you will need to understand how to define a helix and there are many options.  For a helix used for a thread most people would define the helix by its pitch (1.0mm for the metric example or 1/20" for the inch example I gave above) and either the number of revolutions or the length.

           

          Now, to read further into your situation.  It sounds like you are describing a turnbuckle for the cable tensioner.  These have left-hand threads on one end and the normal right-hand threads on the other.  However, your last question is really the right answer; you typically do not model the threads, but just note them.  SWX makes that easy too.

          • Re: Thread modeling
            J. Mather

            Matt Thomas wrote:

            .... Ok, so my question is, does the spiral have to be exactly the same length as the hole that is to be threaded or can the spiral jut out a revolution or two from the back side of the hole? 

            It sounds like the book is having you go through the process of modeling the threads.

            This is an excellent method for learning all about thread geometry and nomenclature.

             

            Out on the shop floor the cutting tool would have to enter before the hole and extend beyond the end of the hole (for a through hole) to get a full formed thread.  So yes, extend your Helix at least the width of the 60° cutting tool beyond the end of the hole.

             

            Attach your *.sldprt file here and end all doubt.

             

            Q1.  Why, oh why are you using SolidWorks?


            Hint:

             

            A1.  Because it is much easier to describe geometry with, well, geometry - than it is with mere words.

            Attach your *.sldprt file with each end every question and end all doubt.

             

            Edit: If it is a blind hole you should (almost) never ever tap to the bottom of the hole.  The machinist out on the shop floor will not appreciate your efforts when they break taps bottoming out.  Leave about 1.5 pitch min from the bottom.

              • Re: Thread modeling
                Matt Thomas

                ok, i can attach the part haha. Im guessing off of you post that i should always attach the part im working on?

                 

                Thanks for informing me that with a through hole, that i should extend the spiral a revolution or so beyond. I was worried that i had to do some number crunching to get the EXACT revs like the book did.

                 

                Looks like next class session, if i remember to, i will try out the method with a blind hole to insure that the threads are not all the way to the bottom of the hole.

                 

                Anyone here of a website called praticalMachinist.com?

                 

                thanks again. ill attach the part soon

                  • Re: Thread modeling
                    J. Mather

                    Notice that as the fastener turns it will hit this ledge and dead-stop.

                    That is not correct - the helix needs a couple of more turns to clear the hole.

                    What specification were you given for the thread - should be a code something like 5/16-18 UNC.

                     

                    Full Thread.PNG

                      • Re: Thread modeling
                        Matt Thomas

                        No codes provided or what type of threads it is for. Juat told me to make a helix pattern with a .025 pitch and 11 revs and 0 degree starting point. I tripple checked to make sure i disnt miss anything, such as type of thread or how he came up with the numbers he did. No discussion on threads or charts found in this book.

                         

                        Thank you for the image. Apparently 11 revs was flush but not enough haha. Ok, time for me to calm my frustration and think through this. I will say this, going through theae frustrations is teaching me alot about problem solving and paitence haha, mostly with myself:)

                         

                        Thanks

                          • Re: Thread modeling
                            Dan Golthing

                            why do you have to draw the threads?  It's nice, but for manufacturing you can simply use the hole wizard which will leave a simple hole in the part and then you will call out the threading operation on the part drawing.

                              • Re: Thread modeling
                                Matt Thomas

                                Its an assigment for my class and its the first time us solidworks students have seen it. But instructor did tell us that its complecated to do threads and to just call them out on the drawings

                                  • Re: Thread modeling
                                    Dan Golthing

                                    It's not necessarily complicated.  Especially now that SolidWorks has a built-in thread feature.

                                     

                                    showing threads is a mixed bag.  In some cases, it looks much better and is more distinguished on a drawing, which will help ensure the part is made correctly.  A shop shouldn't miss a thread callout, but they do quite often.

                                     

                                    On the other hand, the threads will slow performance as the assemblies get bigger.