【转帖】novice looking for constructive criticism on runout and posi

yang686526

novice looking for constructive criticism on runout and posi
i've read through several pages of posts going back about a year looking for help but was unable to find anything that really clarified things for me. many of these posts (without seeing a drawing of the part) quickly went over my head as the dsiscussions went on. i have no training or experience with gd&t, just what i have picked up through reference books and web sites like eng-tips. i am pushing to get some training but it doesn't look promising, at least in the near future. so pretty much i know enough to be dangerous so i am looking for someone to review a drawing of a part that will be outsourced. eng-tips seemed like a good place to get the best feedback because of the number of people that could look at it and from what i have been reading in previous posts some pretty knowledgeable people. my actual questions are below.
i have attached my drawing so that you can see what i have. on this part is is important for the bearing surface (datum b) to be centered on the circular hole pattern. i still need to review the runout and positional tolerances but this was my best guess starting out. i'm sure there are a few different ways to go about this but i'm trying to find out if i have interpreted things correctly with what i have used. how would you interpret this drawing? does what i have done make sense? is there an easier way to do this? just looking for as much feedback as i can get. i do wish i had a copy of the standards to have as a reference as i'm sure this would be part of someones reply but i haven't been able to get this yet because we do so little gd&t here.
just glancing at your drawing, i would suggest controlling the runout of datum b to a, then positioning the hole pattern relative to datums a & b.  controlling the holes to datum b will get the result you require from a functional standpoint.  otherwise, your drawing seems to define the part well.
a few suggestions on that drawing.
the bolt circle should not be a datum (datum c in this case) and it should be a basic dimension. it reflects the theoretical location of the holes (true position) using polar tolerancing.
the total runout on the datum b surface is now redundant. you achieve a relationship of the 6 holes relative to primary datum a and secondary datum b with no tertiary needed. take out the total runout.
to be truly picky, the basic dimension of 60 degrees should be 6x 60 as a basic but that is nit picking.
i have seen a lot of drawings over the last 20 years and yours is not too bad for a self confessed gd & t virgin.
dave d.
dingy2,
nitpicking i am familiar with, doing too much myself.  good catch on the redundancy.
here's a question that i have never been able to give a good answer for:  should the (basic) angle callout be "6x 60" or "5x 60"?  why?
i agree with the others.
also, what is ".125-.188 flat"? is there a flat on the dia? if so, where positioned in relation to the holes?
and ... the small r.03 shows a tol of +/- .06 ??
for the m8 thd, is there a req't for the drill depth?
chris
solidworks 06 5.1/pdmworks 06
autocad 06
ctopher -
the "flat" is refering to a flat on the shoulder perpendicular to the diameter axis. this may need to be reviewed for clarity to avoid this possible misinterpretation.
as for the r.03 and drill depth thanks for catching that.
everyone - thanks for your input, i appreciate it.
ewh:
the basic dimension of the angle should read 6x 60 as per asme y14.5m-94 page 138 fig. 5-39.
one has 6 holes of an angle of 60 degrees.
in the asme example, we have 8 holes @ 45 degrees and the basic dimension is 8x 45.
i also agree with chris - is there a relationship on the flat to the position of the holes. there doesn't seem to be any visual location of the flat but that is not gd & t. i was just looking at the gd & t application.
dave d.
but couldn't one also have 5x 60 degrees to define the 6 locations?  since they are basic dimensions, there would be no tolerance stackup, and you are only need a total of 300 degrees to properly locate the holes.  why have an angle dimension between the last hole and the first hole?  does it actually add value to the drawing?
i realize that i am being somewhat facetious, but still...
i do sometimes like to understand the logic behind things such as this (if there is any).
ewh:
we are not stating the number of holes but the number of angles to the holes.
if you have 6 holes in the example, we also have 6 angles so the basic dimension would be 6x 60. count them up. we do have a total of 6 angles.
dave d.
but you only need five to accomplish locating the holes.  i think i'm beginning to understand your reasoning, but it still seems a little like double dimensioning to me.  i don't see how you could count all six if they were +/- toleranced, though.