huangyhg

datum needed?
please take a look at the attached image.
do the hole centerlines imply that the outer edges are square with the hole pattern? or do i need a clocking datum (one of the widths) to line everything up correctly?
thanks!
i'd say you need the tertiary clocking datum to ensure correct orientation. what you show on the right could happen.
also, (sorry if this is just a sketch and i'm thinking too much) the 6.00 & 10.00 should somehow be tied to datum b. otherwise allthough shown 'centered' there's no explicit tolerance on how well centered.
kenat,
ya, this was just a quick sketch so there are some small things wrong. thanks for the help.
surface a restricts three degrees of freedom and the big hole datum b restricts two degrees of freedom, so the part may rotate around the big hole, you need a tertiary datum to stop the rotation.
if you are using the two small holes as datum b, then you don't need the tertiary datum.
seasonlee
i think you answered your question as soon as you used the word "imply".
this is one of the parts of gd&t i have not messed with. so would my example (attached) work for this situation?
btw, the hole callout for {"dia".250 thru} should read {2x "dia".250 thru}. other then that, please feel free to comment.
v/r
nathan
cad technician/iso director
nrostander what you show is more or less correct but, reflects a different intent/function. in the op the large hole is the datum, for you your overall width & height are the datums. which is correct may vary based on end function.
i'll assume block tols cover the overal dims. also you have an issue with your decimal places not matching between basic dimension and fcf assuming your drawing is inches per 2.3.2 of asme y14.5m-1994.
kenat,
1. what is the tolerance of the hole size ? one need to know since you add material modifier.
2. again, the basic dimension should be three decimal places to match with the positional tolerance.
seasonlee

kenat & seasonlee,
your comments are dully noted. as for the fcf decimal places, i ment to make them 2 place. i blam that mistack on my use of quick sketing and fat-fingering the fcf's. they should read {"dia".05}.
also let me say, that you two would defenatly be great brains to pick for a month strait. unfortanatly that would be impossible.
v/r
nathan
cad technician/iso director
your comments are dullyfff"> noted." - yeah, gd&t doesn't get very exciting.
as for your compliment, thanks, but trust me, there are much better than i that frequent this place. i just try and answer the ones within my limits so i can get help when i need it on more complex stuff. there aint enough to spend a month picking!
kenat,

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