【转帖】specifying gdt on a hex machined nu

yang686526

specifying gd&t on a hex machined nut
hello, i am trying to define gd&t on machined hole inside a hex shape.
nut is forged and then machined. inside machined hole has to with in .005" of outer hex shape.
thank you !
iso 4759-1 tolerances for fasteners 鈥?part 1: bolts, screws, studs and nuts 鈥?product grades a, b and c section 4.2.1.2 tolerance of position appears to be directly suited.  it shows the pitch diameter dfff"> is datum afff">.  the width across flats sfff"> has a true position tolerance tfff"> (at maximum material condition) with respect to afff"> (also at maximum material condition).  the magnitude of tfff"> varies with the magnitude of dfff">.
regards,
cory
bmdesign,
   not enough information.
   what are you trying to accomplish?
                             jhg
if i understand what sm design is saying, he wants to use the forged hex as a datum to locate the internal hole. nothing said about a thread. corypad's reference seems to be just the opposite.
question: are you using the forged hex as is, or is it too being machined?
one way might be to clamp the hex in v's as an equalizing datum, asme y14.5-1994 figure 4-38 (page 78)as is often done with castings. it then becomes a b-c datum for locating the internal hole positioned with respect to datums a and b-c.
the original post is unclear at best.  what is the word "define" supposed to mean?  applying gd&t requirements to a drawing?  measuring them in a lab?
the word "nut" is used, implying an internal thread.  the thread is the datum for fasteners, with other dimensions referring to it.
regards,
cory
yes, sorry,  it probably is a threaded hole since he call the part a nut. it is a good and normal practice to think of the thread as always the datum, but if you are going to tap a piece of hex stock, which comes first? what do you use as a datum to locate and tap the hole?
thank you for the replies & sorry about not giving enough information.
-nut is forged in hex shape, and forged hex shape is not machined after.
-based on these hex flats, threaded hole in the center need to be machined.
checkerron, you are right i want to use the forged hex as a datum to locate the internal hole. also i did check the fig.4-38 in asme y14.5m-1994, but did not understand much...
corypad, it is 28mm threaded forged nut. each nut is forged and internal hole and thread and chamfer is machined. i beleive our supplier is machining it on milling machine, because of that hole is accentric. to control that i have to specify the tolerance.
i am still not clear how will the datum be defined with the outer hex.
the gd&t on the drawing is to show someone how to measure the part after manufacturing to show compliance to the requirements.  it is not used to tell someone how to make the part.
i believe my reference is the exact one you need to measure your part for an accurate relationship between threaded hole and outer hexagon.
regards,
cory
you are right cory, forged hex surfaces need to be defined datums first, and threaded hole will reference to the datums.
while it isn't used to tell how to make the part, gd&t is used to tell how accurate to make the part.
ewh,
i believe the purpose of y14.5 is to define the method for defining and inspecting the required accuracy of the part definition.  accuracy is another thing.