True Position and Bidirectional Control

The position symbol is one of the most useful symbols in GD&T because it creates a diametric tolerance zone that more closely aligns with the functional intent of a feature. But did you realize that you can use the position control to allow more tolerance in one direction and less in another? In this video, Jason explains how to achieve bidirectional position control through the use of a Multiple Single Segment Feature Control Frame.
Interested in learning more about Print Reading or GD&T? Check out more of our free GD&T resources here:download.gdand...
#gdandt #trueposition #multiplesinglesegment

[@Fredumaction]

Hi as a teacher of Mechanical Engineering, I find your videos a great resource and encourage my students to watch them. Thanks

[@marcolima89]

What would be the difference if you used a composite position tolerance, instead of a multiple single segment?
And is there an equivalent to composite tolerance in GPS?
Thanks!

[@Gdandtbasics]

This is a tricky concept to explain quickly however from a high level, composite lower frames ONLY control orientations of the pattern and not locations with respect to the datums. Where MSS will control locations. There are some configurations of upper and lower frames where both the interpretation of MSS vs composite would be the same. And to the best of my knowledge there is nothing in the GPS that is similar to the Composite control. Thanks for the question!

[@marcolima89]

@@Gdandtbasics thank you for the explanation.

[@TAH1712]

I get the concept but the LH edge is up against another part as you've shown - naturally I wouldn't expect to loosen up that position to C datum.

[@asaholey]

Agree. Wrong example. And also the hole the diameter 6.25 doesn't have tolerance in the callout.

[@TAH1712]

@@asaholey oh yes agreed...

[@Gdandtbasics]

you're definitely right that this design might not benefit from extra tolerance with respect to C. And for the tolerance on the Ø.625 thru hole, we have to rely on the lazy/forgetful designers best friend "UOS Tolerances" in the title block XD. Sorry for not including that here!

[@asaholey]

@@Gdandtbasics that's very important for people who still learning because sometimes can be confusing

[@TAH1712]

@@Gdandtbasics thank you for your reply...

[@EricIrwin]

I just want to point out that dimensions 6.000, 2.750, and 3X .250 are shown as basic and thus have no tolerance. I know that this drawing is not complete but I think people should be aware that those features need to have tolerance applied.

[@Gdandtbasics]

Thanks for pointing this out! These could easily have a profile of a surface added to the surfaces in the drawing views or rely on an UOS Profile Tolerance in a title block.

[@TAH1712]

I think with only 4 viewers adding comments despite the 21 or so likes, many views aren't critical and self thinking...

[@chrmeiss67]

Sorry, but the datum system doesn‘t follow function. Clearly B is primary and A-C-D-D are secondary (D-D is two times derived features of the two holes dia .625). Nominal lineare sizes of through holes and A should be designed at MMC and their derived features should be specified with position and maximum material condition at clearance zero.

[@Gdandtbasics]

@chrmeiss67 Love the enthusiasm, and i do love me some zero tolerance at MMC as well! I would take that argument even further and say that Datum Feature B in our example is a great primary datum feature and the pattern of two holes should actually be the secondary datum feature only. However this was just a simple example we used to quickly explain MSS Position controls.
Check out our video on patterns of holes as datums. th-cam.com/video/f4A2BGX9HLw/w-d-xo.html