Interpretation of single segment feature control

[brandnew1]

i believe i have this interpretation, but i wanted to run this by all of you just to make sure i'm on solid ground.

When i think of true position i think about the formula:
True Position = 2? Deviation in X² + Deviation in Y² and i think of this in terms of diametrical situations.

Per the attached pdf, the .010 true position to datum B doesn't appear to be a diameter. So will this be a straight .010 plus or minus value for each side alone?

Thank you

 

[KENAT]

Bottom frame is linear tolerance zone, virtually a +-.

However, isn't the bottom frame still to be refinement, so should be smaller than top.?

Also, how is slot width position controlled by a diametric zone?

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[brandnew1]

Thanks Kenat,

i thought the bottom would be +/- .010. This is how the blue print is showing this callout (the previous attached pdf shows teh front view on top and side view on the bottom)

Datum B (which the bottom portion calls out to) actually still is a forging. We only deal with the inside portion (Datum A).

The way i interpreted the drawing (please correct me if i'm wrong):
- the slots themselves (midpoints) need to be within +/-.0005 (tp of .001) to Datum A (which is machined here), so a straight line will go right through both slots and the center point of Datum A and be off no more than .001.
- For the bottom portion, Datum B is this forging that basically is a straight line parallel to an imaginary line created for the first true position of .001 to Datum A, or actually vice versa where the slots machined will be +/-.010 to this forging line (Datum B).

 

[brandnew1]

i apologize, i updated the pdf i placed on...the side view was a sectional view...the slots are shown on the bottom right image.

 

[Belanger]

The diameter symbol merely connotes the shape of the tolerance. Without a diameter symbol, the tolerance zone is no longer a cylinder, but rather it is planar. So for that lower frame, think of a bandwidth of .010 which is centered around datum B. That means the slot's center can be .005 to either side of datum B.

That said, I can't really tell what the datums are. And it doesn't seem right to have the diameter symbol in the upper position tolerance -- it's a slot. (Also, Kenat, I don't think the lower frame has to have a smaller tolerance value than the upper frame since they reference different datums.)


John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[SeasonLee]

The slot is not a circular feature, so the tolerance zone is not a cylinder, diameter symbol in the position callout is not necessary here, and the position callout for a slot indicates symmetrical relationship between feature of size.

The datum symbol B can not place it on the center of the feature, and datum symbol A put it on the feature of size will be better for this case.

SeasonLee

 

[brandnew1]

Just to add to this, Datum B to the Center of Datum A is suppose to be 1.000", however this is not boxed in giving it a +/-.010 tolerance.

This was throwing me off in terms of the results attained on the CMM. With true position call outs i think i tend to see this tie into a basic dimension, giving the true position a tolerance. But in this case the true position isn't tied into a box dimension, so this slot to Datum B can be +/-.005 to a dimension that has a tolerance of +/-.010.

Is this an accurate way of viewing this? (e.g. the distance from Datum B to Datum A is .995 (within the .010 tolerance), the slot distance then can be .990/1.000) or if i have another part that measures 1.000, the slot distance can be .995/1.005)