【转帖】dimensioning on drawing with gaugegage barball

yang686526

dimensioning on drawing with gauge/gage bar/ball
i have a drawing for checking that has a dimension scheme similar to the attachment (it’s a channel/slot not a c’bore hole).
i have concerns about the way it’s been done but it’s not a type of scheme i’ve really used much before.  i looked in asme y14.5m-1994 and don’t see dimensioning in this way addressed.
so i’m wondering if i should re-dimension it using surface profile (similar to discussed in
i've done it that way before and got no flack back. see attached.
i consdier this a "conventional" dimensioning method. if you want to control the feature using gd&t well... then you'll need to have the confidence in your shop that they can understand it. in my case they couldn't.
---sw 2008 sp1.1---
kenat,
   definitely, i would show basic dimensions to the slot edges and the angle, and then apply geometric tolerances.  as the inspector, i would select the inspection bar.  perhaps it would not be 1" in diameter.  perhaps i would repeat the test with several sizes of bar!
   as shown, you do not have tolerances on the drawing.  i do not see a way to apply tolerance that were not ambiguous.
   i would use some combination of profile tolerances, angular tolerances and perhaps even a positional tolerance.  it depends on what you are doing with it.
   you could apply a tolerance on the round bar, and then a positional tolerance, effectively specifying the inspection tools.  i do not know how this stacks up against the standard.  this might be a good functional specification, but i would prefer the gd&t, above.
                         jhg
here's the attched. 2nd attempt.
---sw 2008 sp1.1---
thanks barm, out of interest what is the tolerance info on your sketch, espeically on the 1.125?  i assume this has some kind of special control as it's labelled critical, or is this an inspection issue?  also where you 1.175 says part size is this meant to imply it's a perfect diameter or does it still have some tolerance on it.
on the drawing i have it has block tols +-.005 for 3 dp,  +-.010 for 2 dp and +- 1/2 degree.  as drawn i'm assuming this applies to the height and the diameter.  this leads to quite a bit of tolerance build up.  the diameter represents the diameter of the part being clamped although the part is actuall +-.002.  
i'm inclined to agree with you drawoh about probably using profile tolerance , a bit like either 6-23 or 6-24 but obviously linear not conical.
kenat, probably the least qualified checker you'll ever meet...
kenat,
going by memory cause i don't have the completed drawing anymore.
tolerances from drawing tittle block may have been.
xx = +/-.010
xxx = +/-.005
angles = +/- 1/2 deg.
this is a 1/4" thick plate used to clamp/locate a part. the part is a forged valve. the valve needed to be clamped prior to being machined.
so.... my toolmakers didn't need to have the drawing "hold their hand" by me over tolerancing/dimensioning the drawing. i did want to highlite to them the importance of comtroling the center of the 1.175 dia. this dia represented the nominal size of the valve.
the toolmakers may have machined up a 1.175 dia rod, set it into the "v-plate" and measured to it's top side to calculate the center "critial" dimension.
again, our engineering department likes to use gd&t but if the toolmakers aren't comfortable using it then we used the conventional method.
note. if we were dimensioning gauges used to check production parts then we almost always used gd&t. it's way more precise. the toolmakers would then need to rely on our inspection department to ensure comformance to the drawing.
brent
---sw 2008 sp1.1---
thanks barm, while the parts i'm working on are for tooling fixtures they're used to align a critical component of our product.  also they'll be machined externally as we don't have a machine shop so...
i think i'll go with surface profile.
thanks to both of you.
ken
kenat, probably the least qualified checker you'll ever meet...
one correction i would suggest on the attached sketches, and that is dimensioning to the top of the gage ball (direct measurement, not to its' centerline.
thanks ron, that's what i was thinking.
however, i think i'm going to progress with surface profile.
kenat, probably the least qualified checker you'll ever meet...
yes, i agree with that or provide it as a reference dimension.
---sw 2008 sp1.1---
kenat,
i have just one final option that i'd consider in the future. see attached.
the gauge pin can be any standard size approx. to the dia. called out on the drawing. all other dimensions carry a +/-.010" tol. therefore the center of the gauge pin being the tighter controled feature get the necessary attention. the positional callout has a 3d control applied which in my opinion is suffice for the application.
brent
---sw 2008 sp1.1---