【转帖】runout to threads. possible

yang686526

runout to threads. possible??
questions for gd&t'ers: can runout or
total runout be applied to threads (external or internal). my gd&t books only shows examples to circular surfaces o.d.'s
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since runout is usually checked by a dial indicator in one full rotation, and since the thread callout applies to the pitch diameter unless otherwise specified, it doesn't sound like a good way to go. consider postitonal tolerance instead, and consider what your circular datum surface is that you need to check the thread to. often the postitonal tolerance is modified as applying to the major diameter (external) rather than the pd. use the pd if your using thread checking gages.
why would any one wants to use the thread as a reference feature. usually threads (even the 3a and 3b classes) have tolerances that are probably larger then the run out requirements. this requirement will complicate the threading process and it will be much more expensive then just check it by gages.
from my experience, inexperienced engineers and designers are tempted to use threads for centring two parts. this is a bad approach. the better is to add a short accurate cylindrical part to the threaded part and use a loose (2a, 2b or even 1a ,1b class) thread. the cylindrical part will be used for centering and the loose thread for connection.
i'm with israelkk ... why would you want to?  the errors in the thread faces would make take it outside of any value you would expect.
jim sykes, p.eng, gdtp-s
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i do the same as israelkk. use a dia for centering, where you can use runout if needed, then the thread for holding.
i would never use runout on threads.
chris
systems analyst, i.s.
solidworks 06 4.1/pdmworks 06
autocad 06
both circular and total runout can be applied on small cylindrical features that share the same axis and should be checked not on cmm but with a divider head or chuck and digital indicator on a base.
it is not good practice to reflect threads since the areas of contact are so small that whatever result one obtains would only achieve about a 70% confidence.
even if one uses a flat contact on the indicator, it is difficult to check and i am talking about an od thread.
don't even think about applying on internal threads. it won't work.
hope this helps.
who said anything about using the thread as a reference feature? not knowing what the design looks like, we wanted to have the thread datumed to and adjacent feature---functional, circular, and on the same axis.
i would not want touse a thread as a referance simply for the fact that threads will have more than one precise diameter, would not be a place from which you could take precise measurements and all this could be cause for considerable inacuracy and problems in the shop. try using a simpler point as a control referance.
ok, the op asks if runout can be applied to a thread, not referenced from a thread.
i am in agreement with others here that positional tolerance would be a much better control.
a great use of experience answered my question. thanks guys. i knew
that runout or total runout cannot be used on a threaded integral stud.
or an internal thread say 2 1/4 size in a circular part. i work with some old
school prints and co-workers who may have heard or read gd & t and
misinterpret. how to tell them the truth. why bother. a precession arbor
is what the shop uses to check this. i would stick to true position and perpendicularity to a
datum if need be. for future experience with another company.
good luck.
i'm going to runout of this thread now.
chris
systems analyst, i.s.
solidworks 06 4.1/pdmworks 06
autocad 06