【转帖】counterbore

yang686526

counterbore
hi everyone. i submitted this question august 28 and only had one
response. let me reword the question. figure 5-37 in the standard for
positioning a through hole and a counterbore hole with one positional
control. the question is, does the through hole and the cbore hole have
two different zones with the same tolerance size where the cbore hole
can tilt or shift in a different direction than the through hole, or
the two diameters must have one axis within one zone for the length of
both features?
check out our whitepaper library.
please ignore the august 28th date. it was from a different memo. i do not know how to delete the statement.
gary,
perhaps the committee violated one of its fundamental rules here in specifying a manufacturing process.  perhaps the proper way would have been to specify the diameters individually with the tolerancing as required to provide the proper clearnaces for the head and the body of the screw.
but as far as the example goes, i would have to go with a single tolerance zone for both features simultaneously.
they are two individual features therefore an axis can be constructed for each feature independently.  
  the axes of the two features must fall within the same tolerance zone but they are independent of each other. reading 5.7(a) on page 135 it says "identical diameter tolerance zones for hole and counterbore are coaxially located at true position relative to the specified datums". this is a clear indicator that the tolerance zones, although identical, are separate.
ringman,
i don't see where there is a manufacturing process specified. what am i missing?
powerhound
production supervisor
inventor 2008
mastercam x2
smartcam 11.1
ssg, u.s. army
taji, iraq oif ii
i have always thought that cbore was manufacturing process which required the use of a counterbore (tool) .  would that not be specifying the process rather than the geometric definition?
i would make one callout for the hole and cbore, and one fcf for it. treat them as one. it would be up to the machine shop if they want to machine them separate, but within the tol indicated.
chris
solidworks 07 4.0/pdmworks 07
autocad 06
i agree that we have 2 features with the same tolerance and are independent of each other.
dave d.
my understanding was as majority of posters and as detailed by power hound.
that said this often seems to be overlooked by others, many assume the cbore & hole are automatically co-axial, this includes people that prepare standard hole charts etc.
my checker actually went through a hole chart we'd been using and made this correction.  of course now i'm not sure they match standard c'bore tools, sometimes you can't win!
kenat, probably the least qualified checker you'll ever meet...
ringman,
  counterbore is what the feature is called, like countersink or counterdrill. the tool and the process may share the same name, but the feature is what is being referred to in the standard. they don't care how you apply the counterbore, it just needs to be there. on a cnc mill, i never use a counterbore tool to apply a counterbore, i interpolate the larger diameter with an end mill.
powerhound
production supervisor
inventor 2008
mastercam x2
smartcam 11.1
ssg, u.s. army
taji, iraq oif ii
as of this date, it is 5 to 1 in favor two separate axes.
it is my opinion, one axis for the length of both features:
1. figure 5-37 states 0.25 positional tolerance zone for hole and counterbore.  not zones.
2. it does not make sense to have two axis going in two directions.
3. i think it implies one tool and one axis the total length of both features.
4. if the workpiece cost thousands and the two features were machined separately at different angles within the 0.25 zones with no assembly there would be litigation.
5. the bottom line is to state on the drawing next to the position callout the intended definition.
gary