huangyhg

default profile callout
for drawings that might have a default profile callout, how is the specification in section 6.5.1 para. (a) reconciled?
(a) "an appropriate view or section is drawn showing the desired basic profile."
i take it that this is in reference to the 1st sentence of the 1st para. in 6.5.1;
"the profile tolerance specifies a uniform boundary along the true profile within which the elements of the surface must lie."
designbiz

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are you talking about true drawings or hybrid drawing/mbd?
for a true drawing then you need a view that shows the desired basic profile. just instead of having an fcf attatched to that geometry in that view, you rely on the general note.
or am i missing a trick question here?
for mbd you'd have to also apply 14.41.
(please note, i'm not completely sold on the idea of routinely having a default profile on drawings, but i don't see your above question as the deciding factor on why you can't)
kenat,
kenat,
this is not a trick question, however i would like to consider comments from others. from what you write,
i think we are in the same camp.
our drawings callout tolerance of position for holes. all other features are claimed to be the master and basic based on the math data (cad model). a general profile callout is used to default to everything else. sometimes inexperienced folks dont even bother to identify datums a, b, and c which are referenced in the default profile note.
i have found out that if the drawing doesnt define the datums, then it is suppposed to be defined in the model with 3d gdt (ungrahics here). it isnt. i question on how the callouts are suppposed to be interpreted. this falls on deaf ears.
i say as you have that at a minimum the view on the drawing representing true views of profiles left to default should be present.
i believe this a decision to save time by not having to actually spend time dimensioning. however in the effort to save time i see many times that even part functionality is not thought about. in the long run just more "hybrid" drawings that have little to no meaning.
just wondering what folks do with these drawings when they are used to create parts. astonishingly as i have asked "who" inspects and "how" is it inspected, more often than not nobody seems to know who or how? sad for a fortune 100 company.
designbiz

so you are talking about at least partial mbd? definitely look at y14.41-2003 if you haven't already, i can't seem to find much now but 6.2.6 does mention that general notes may include tolerances for the entire model and 10.1 mentions general geometric tolerance.
i thought it said more somewhere about default surface profile notes but i can't find it now. you've got me doubting myself.
in y14.5m-1994 look at 6.5.4, it appears that datum references aren't always required. however, in this case, i share your concerns about repeatable inspection etc.
quote:
i have found out that if the drawing doesnt define the datums, then it is suppposed to be defined in the model
could you cite a reference for this, as i believe it may conflict with 6.5.4 in 14.5 above, unless 6.5.4 is only allowing for use of surface profile without datums in coplaner controls (like flatness for multiple surfaces). i did work on a hybrid model/drawing mbd with a surface profile but no datums a few months back, it was an interim drawing until we could get some datum features cast in for use to reference.
however, my comment about having a view showing the profile was talking about stand alone/fully dimensioned drawing not mbd.
kenat,
there is not a y14.5m standard that i am aware of regarding the datums attached to 3d models. this is internal to this company and refers to the capability to attach gdt datums to features of the actual 3d model. these datums can be viewed if the correct software switches are turned on independently of the drawing.
as to my initial question regarding partial dwgs that reference the y14.5 standard,as i have described, and what do the profile defaults apply to. considering that this line of thinking eliminates drawing views that desfine a particular profile, is this legal and understandable according to your knowledge of the standard?
section 6.5.4 does mention use of datum reference for profile callouts that control orientation and/or location.
this is the case for us. no features, except for holes are defined on a drawing. additionally we do not reference y14.41 and unfortunately i dont have access to a copy at this time.
designbiz

doing partial mbd without invoking y14.41 and relying on the 94 version of 14.5 sounds problematic. fundamentally y14.5-94 isn't set up to support that and i suspect you'll find quite a few issues like this if you look close enough.
however, you mention an internal company standard, if well written it's entirely possible this company standard covers these types of issues.
without knowing what your internal company standard says it's difficult to give much input.
kenat,
i'm going to jump in here and ask a question. on the drawings i've been working on i would like to apply a note that controls flatness of all surfaces. is there any preference to flatness vs profile when doing this? i assume a profile callout without referencing datums accomplishes the same thing as a flatness callout.
kenat,
unfortunately this isnt even a company standard. nothing is written anywhere. it is a verbal edict.

designbiz

dbiz, then you have my sympathy. i actually want to update our in-house drm to try and give guidance on hybrid mbd as at the moment, most people do a crummy job of it. i do intend referenceing 14.41 for what it's worth - it doesn't answer all the questions and seems aimed more at cad developers than actual users as i think fcsuper has put before.
jlang, might be better for a new thread but simplistically. for a single surface, flat to itself, arguably either would probably work but flatness would probably be better understood by the masses and this is it's intended application. if you have coplaner surfaces you want flat 'to each other' then you need to use surface profile see 6.5.6 of asme y14.5m-1994.
kenat,
jlang,
i personally dont like general defaults as a shortcut. if you are going to take the time to label a surface and then reference that surface to a note; then why not just add the gdt flat control while your at it and eliminate possible confusion? if its important enough to identify a surface for a tolerance that is typically associated with flatness, and the associated costs of that tolerance, why not take the time to identify it?
if it is flatness that you want to control, then why not keep it simple and specify flatness.
obviously there is more ways to control a feature than just one and it would be up to the individual when it comes to a preferred way, not withstanding that functionality be considered foremost.
designbiz

thanks for your inputs kenat !
designbiz

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