True position callout with non datum axis basic dimensions (using OGP measurmind software)

[Langless28]

I am trying to figure out how to setup this TP callout using an optical CMM (OGP). I would be able to do it if both basic dimensions were on datum axis but the basic dimensions for the TP callout is on Y and a straight line basic dimension.

I guess the question can pertain to using the software more than anything.

I have attached a small screen capture of the print which should show you what I mean.

 

[Langless28]

This is not a post machined part. For the most part, we are achieving the tolerance to print from the injection mold. The most critical feature is the nub and it was a good thing I started questioning it because it proved to be out of tolerance.

3DDave; There is no sorting as currently, there is not "good" and "bad" parts. They are all functionally working. Now functioning and functioning optimally are two different beasts and i hope to hone in on the ladder. This also needs to be done because we are preparing for a material change and I know the new parts will not pass the FAI unless the print undergoes some changes.

I also attached the entire drawing.

 

[3DDave]

If the parts were drawing compliant, which they apparently aren't, the parts would probably not work. The parts should have all been rejected. Unless the molds are scrapped and new molds made, there is nothing on a drawing that will affect how the parts can function, optimally or otherwise.

As-is, the drawing is missing too much information to repair. There needs to be a tolerance scheme devised for the entire assembly that this is part of and then tolerance analysis based on existing production capability to determine what might be done to correctly dimension and assign tolerances to a new drawing for this part, and probably most of the other parts.

Since the nubs aren't features of size, they aren't good candidates to establish a DRF, though limited surfaces of them might be used as datum targets.

To make one interpretation correction - A is the centerplane of the .170 thickness of the part;

 

[Langless28]

3DDave, how is A interpreted as the center plane?

I have to disagree on the parts not meeting the print cant work, I have physical evidence of that. that being said I have the opportunity to obviously open up some tolerances. Since this lever rotates about "b", as long as the 3.956 dimension is achieved, it's irrelevant where the nub lies in y with respect to the lever faces. At some point being out in y would cause an issue but on these parts currently it's not an issue. That is why i was asking for a new scheme on how to hold the straight line tolerance and diameter but be a little lax on the y dimension.
I am not going to make a new $35k mold if I can make a print update to match the tooling output because functionally, the parts off the tooling are perfectly acceptable.

While we're on this print, in regards to a lot of the middle view true position call outs ( on the slots and ovals), are they incorrect because there is no basic dimensions referencing them?

I appreciate all the good information, this is really helping me understand better.

 

[M4C7]

how is A interpreted as the center plane?

When a datum feature symbol is attached to the size dimension of a width feature of size, the center plane of the width feature (to be precise, the center plane of the true geometric counterpart) becomes the datum plane. See attached Fig 4-13.

If you instead attached the datum feature symbol to the feature surface or an extension line, then the surface itself would be the datum feature. Again, please reference attached image.

 

[3DDave]

A is the center plane by definition. It's also what locates the slots. It is right in the standard.

 

[SeasonLee]

Yes, A is a center plane. If the datum triangle symbol is placed inline with the size dimension, then the center plane is a datum feature, here is an excellent example from Tec-Ease. If the datum triangle symbol is placed offset from the size dimension, then the datum will be the one as you mentioned.

https://www.youtube.com/watch?v=OJR3HQYsTVk

Season

 

[SeasonLee]

in regards to a lot of the middle view true position call outs ( on the slots and ovals), are they incorrect because there is no basic dimensions referencing them?

The diameter symbols need to be deleted as indicated by the arrow, since it’s just a width not a circular feature. The position callout here means the symmetrical relationship between features of size, the distance between the center plane is an implied basic zero dimension, that why you can’t find out any basic dimension.

Season

 

[SeasonLee]

Sorry, here is the attached file.

Season