【转帖】gdt suggestions needed

yang686526

gd&t suggestions needed
i have a situation that i need some help with - here's the background:
a) i am not by any means well versed in gd&t
b) even if i knew gd&t inside and out, there are other groups within my company (qa) that either don't know gd&t or don't have the equipment to inspect drawings that contain gd&t
c) i have a part drawing that, in my opinion, is desperately in need of gd&t, if only on a portion of the part
the part shape is essentially shaped like a block "c", (see attached) and i need to control the two indicated surfaces such that they are on the same plane (within a certain tolerance, of course).  my initial thought is to use datum targets to define a datum on these two surfaces but i don't know if this is the best way to do this, especially given fact b, above.  all suggestions are welcome, including telling me to get training in gd&t!!!  that is part of my long term plan but doesn't address the need to clarify this part drawing, which is immediate.
thanks in advance.
profile!
make one surface a datum and assign profile to the other
-or-
assign both same profile relative to an outside set of datums.
tick,
thanks for the suggestion.  does the attached pdf reflect what you meant in the way of a profile control?
exactly
dgowans,
the requirement for the two surfaces to be coplanar to each other should be controlled using surface profile.  but if you are only concerned about the coplanarity of the surfaces, and not their location and orientation relative to other features, then datums are not necessary.  the callout would look something like this:
spf|.02
2 surfaces
there should be arrows pointing from the feature control frame to each of the two surfaces.
this coplanarity can be inspected using a surface plate and dial indicator:
-place the part on the plate with the considered surfaces facing up
-level the part so that the two surfaces are as parallel to the plate as possible (use 3 jacking screws or something similar)
-sweep the indicator over both surfaces, covering as much of the surfaces as possible
-the total indicator reading (difference between highest and lowest readings) is the actual value for the surface profile
-the leveling of the part can be optimized to get the best (smallest) actual value
i can point you to some good resources for gd&t books and training.  get in touch with me through the contact information on my web site if you are interested.
evan janeshewski
axymetrix quality engineering inc.
tick, evan
thanks to you both - very helpful.