huangyhg

hole position to self?
hello,
i was looking at this print from a supplier yesterday and after reviewing it for a while i came across something i just don't understand.
there is a hole controlled (compound feature control frame) with true position with respect to datums c and a and perpendicularity control with respect to datum a. so i go off and hunt down the location of these datums and i see that datum c is shown to be the center of the hole that's being controlled.
does that make sense to anyone? or is this a mistake?
see attached pdf.
thanks,
mod
is that datum c hanging off of the fcs that is in question. it looks like a "d" instead of "c". if it is not datum c what feature makes datum "c"?
look at the view just above the view that contains the fcf in question and you'll see datum c appended to the axis of the feature.
i really don't know... it looks like they're calling out the axis to be both datum d and datum c....?
....?
the drawing is not per y14.5 in that a centerline alone is not to be used as a datum. this introduces the ambiguity that we see here; which feature is datum c? it looks as if the intention is to define a plane a datum c, then control the hole to that plane and surface a.
good to know you got shoes to wear when you find the floor."fff"> - robert hunter

well then we do not know what "c" is then. there is at least two possible features that can make "c". the "small long pin .100" or the bigger diameter that the small long pin is attached to .155/.133. so i see a light mark up in top right view where there was datum "c" was attached once upon a time. assuming .155/.133 feature centerline is datum "c" then the call out for the fcf in question is correct. it is making sure the .1 center is controlled back to the .155/.133 center. it is not being called out back to itself. it is being called out back to .133/.155 that make datum "c"
that small incomplete datum reference frame is my own sketch... i was simply trying to explain to some other people in my department why this print was incorrect and how it could be remedied.
of course, none of them really know that much about gd&t but think they do, so i've got to do double duty to convince them of anything. that's sort of the reason why i posted here... to gain a little more input about this.
thanks for the replies.
as above c doesn't appear to be properly defined per 14.5, also how can the hole be perpendicular to what they seem to imply c is?
kenat,
i think they're saying that the axis of the hole should be held perpendicular to datum a.
also, it's just occured to me that they were probably trying to call out the axis of the pin on the other side as datum c and then give the hole a position tolerance to the center of that pin (datum c).
so it could all be fixed up nicely if they would just move that datum reference frame from the axis of the pin to its outside surface.
the fcf for the hole appears to say [pos|dia.007|c|a] in the top line. to me this is wrong, the hole appears to be intended to be coaxial to c, not perpendicular to it.
kenat,
position can control coaxiality as well as perpendicularity.
good to know you got shoes to wear when you find the floor."fff"> - robert hunter

does including the perpendicularity tolerance in the fcf function as the only orientation tolerance? or does the first datum callout for true position in fcf always control orientation whether you like it or not?

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