10 Replies Latest reply on Feb 12, 2018 2:25 PM by Gabriel Guzman

    Maximum Material Condition

    Gabriel Guzman

      Hi, Id like to request some help applying GD&T to my drawing, heres a picture for reference.

      Im trying to find a way to assign a bidirectional positional tolerance for the .117 ID (Datum C). Its relationship to OD .619 will not change, Im going to assign it a static tolerance. But when I dimension its relationship to the linear dimension .792 Id like to find a way to express that if the linear dimension .792 is at its smallest size, for example .785 it will have no positional tolerance, but as it gets bigger up to .792 it will gain tolerance. In this way I will be able to control its mating function with the nut that will go over OD .619 and the spring pin that will be installed in ID .117. Im sorry for the lengthy question, but thank you very much in advance for anyone who can help.

        • Re: Maximum Material Condition
          Dan Pihlaja

          Gabriel Guzman wrote:

           

          Hi, Id like to request some help applying GD&T to my drawing, heres a picture for reference.

          Im trying to find a way to assign a bidirectional positional tolerance for the .117 ID (Datum C). Its relationship to OD .619 will not change, Im going to assign it a static tolerance. But when I dimension its relationship to the linear dimension .792 Id like to find a way to express that if the linear dimension .792 is at its smallest size, for example .785 it will have no positional tolerance, but as it gets bigger up to .792 it will gain tolerance. In this way I will be able to control its mating function with the nut that will go over OD .619 and the spring pin that will be installed in ID .117. Im sorry for the lengthy question, but thank you very much in advance for anyone who can help.

          Are you trying to imply that the .117 hole will always be assigned to the halfway point of the .792 dimension?

          This location (IMO) should be driven from the thickness of the nut.

          Instead of doing that, why don't you add a dimension from the right side of the .792 dimension to the centerline of the hole?

           

          Then the location of the hole won't be dependent on the length of the .619 diameter.  Now, you can either add a tolerance to the dimension, or add the horizontal position tolerance and make the dimension basic.

            • Re: Maximum Material Condition
              Gabriel Guzman

              Hey Dan, thank you very much for helping me out. If you don't mind, can I ask, what do you mean driven by the nut? Like if the dimension should be indicated by the fabricated nut? I think that makes sense, but how does that work? Thank you.

                • Re: Maximum Material Condition
                  Dan Pihlaja

                  I didn't mean directly driven by the nut....I meant that what matters is that the nut can be installed.  I guess I don't really know your scenario, but you are trying to specify a relationship between the .792 dimension and the hole placement.  I am not sure that you need to do that.

                   

                  My assumption is that you want to position the hole so that, the nut can always be installed without running into the right shoulder or sticking off the end of the .916 .619 diameter.

                   

                  You should be able to do that without referencing the .792 dimension directly.

                   

                  Does the spring pin go through the nut as well, or does the nut sit to the right of the spring pin?

                    • Re: Maximum Material Condition
                      Gabriel Guzman

                      Good question Dan,

                       

                      The nut covers the OD .619 completely, so yes, the spring pin goes through the nut and the part that is being discussed completely. And yes again, what you said is correct, I just want to make that everything will assembly no matter how far from the tolerances they reach, but of course giving as much tolerance as possible.

                        • Re: Maximum Material Condition
                          Dan Pihlaja

                          Gabriel Guzman wrote:

                           

                          Good question Dan,

                           

                          The nut covers the OD .619 completely, so yes, the spring pin goes through the nut and the part that is being discussed completely. And yes again, what you said is correct, I just want to make that everything will assembly no matter how far from the tolerances they reach, but of course giving as much tolerance as possible.

                           

                          So then, what are the tolerances on the thickness of the nut and the distance from the hole in the nut to one side of the nut?

                            • Re: Maximum Material Condition
                              Gabriel Guzman

                              For the thickness of the nut its .792 +/- .003 and the positional tolerance zone for the center is for the moment .003.

                              Thanks a lot Dan, sorry for the hassle.

                                • Re: Maximum Material Condition
                                  Dan Pihlaja

                                  Gabriel Guzman wrote:

                                   

                                  For the thickness of the nut its .792 +/- .003 and the positional tolerance zone for the center is for the moment .003.

                                  Thanks a lot Dan, sorry for the hassle.

                                  Well then, you are already going to have problems with your nut sticking off the end of your .619 diameter.

                                  The nut has a limits of .795" - .789".  Therefore, if you don't want the nut sticking off the end, then you will have to make the .619 diameter at least .795" long.  That would be your minimum.

                                  I don't know your manufacturing process or the material involved, but lets assume that it is steel and you are turning this on a lathe.

                                   

                                  Then I would make the .619 diameter a nominal length of .803" and maybe give it a tolerance +/-.003"  (you could go tighter very easily [with the assumptions above], but this should be easy to hit). This would make the .619 diameter limits of .806" - .800"  (Other manufacturing process and other material would mean that this could be drastically different).

                                   

                                  Then I would give your hole a dimension from either the right side or the left side of the .619 diameter and give it a position tolerance (either using a datum and frame or with simple linear tolerances on the dimension) of +\- .002".

                                   

                                  This should give you a minimum of .003" of gap between the end of the nut and sidewall (same for the end of the nut and the end of the shaft).

                                   

                                  Again, I don't know your application/material/manufacturing processes, so keep this in mind.

                      • Re: Maximum Material Condition
                        Kevin Chandler

                        Hello,

                         

                        Several items:

                        • Since .619 isn't held except by size, its shape & axis will float within this envelope.
                          • It's on the B datum but its form is not held to it.
                          • What affect this has may not matter.
                          • But since it isn't referenced, the .117 hole will not necessarily be tied to it.
                        • You state the .117 positional relative to the central axis doesn't matter, but the positional tolerance is circular by default.
                          • You'll need to specify different tolerance for vertical vs horizontal if this is what you require (Doable, but as sketched is circular).
                        • MMC variance of the .117 positional tolerance is the hole's material condition.

                         

                        What you need is "datum shift": https://www.quora.com/What-is-Datum-shift-in-GD-T

                        You'll need to create a datum on one end of your .792 dim, but review this video, it should get you started down the path I think you wish to travel.

                         

                        Cheers,

                         

                        Kevin

                        • Re: Maximum Material Condition
                          M. B.

                          Take a look at composite tolerance.  You'll probably need additional datums to use correctly depending on how the mating part is controlled.