## VC and RC

## VC and RC

(OP)

One more question from the Tolerance Stackup book.

Calculate X max and min distance between the edge of the groove and the side of the part.

For the slot I used VC: 3.5 and RC: 4.9.

X max: (10.5-3.5)/2 = 3.5 -- agreement with the book

x min: (10-4.9)/2 = 2.55-book says: 2.3

The book does NOT use VC and RC calculatons, but I guess if the calculations are done correctly they should match.

What am I missing?

If I subtract the form error of the datum feature E (0.5) from the LMC (10.00) and then use RC boundary (10-0.5 = 9.5; (9.5-4.9)/2= 2.3

The question is why should I subtract the form error of "E" when I use VC and RC method and the book does not have to do it when the answer is given? (the book is using 5 (10/2) in the answer.

Part width: 10.00-10.50-datum feature E

Slot width: 4.0-4.2 , pos 0.5 (MMC) with E (MMC)

Calculate X max and min distance between the edge of the groove and the side of the part.

For the slot I used VC: 3.5 and RC: 4.9.

X max: (10.5-3.5)/2 = 3.5 -- agreement with the book

x min: (10-4.9)/2 = 2.55-book says: 2.3

The book does NOT use VC and RC calculatons, but I guess if the calculations are done correctly they should match.

What am I missing?

If I subtract the form error of the datum feature E (0.5) from the LMC (10.00) and then use RC boundary (10-0.5 = 9.5; (9.5-4.9)/2= 2.3

The question is why should I subtract the form error of "E" when I use VC and RC method and the book does not have to do it when the answer is given? (the book is using 5 (10/2) in the answer.

Part width: 10.00-10.50-datum feature E

Slot width: 4.0-4.2 , pos 0.5 (MMC) with E (MMC)

## RE: VC and RC

The conclusion was something like the form error of the datum feature must be considered in order to get the calculation correctly.

If I am not mistaken pmarc showed us the correct calculation.

And BTW is bothering me that I cannot find that thread now. I will keep looking, but in the meantime if someone knows what I am talking about, please post it.

## RE: VC and RC

John-Paul Belanger

Certified Sr. GD&T Professional

Geometric Learning Systems

## RE: VC and RC

## RE: VC and RC

I think this is the thread most relevant with the OP question.

## RE: VC and RC

## RE: VC and RC

Yes. Datum feature E is the thickness of the plate 10.0 - 10.5.

## RE: VC and RC

Does the minimum distance (4.7 calculated minimum distance) change if the OD, datum feature A, is referenced at MMC in the positional callout?

What about if it is at LMC in the same ID position callout?

In other words, position of the ID will have some available datum shift.

## RE: VC and RC

Am I correct?

## RE: VC and RC

So, to re-answer:

4.7 (“X” minimum distance in pmarc’s case) if datum feature A is callout at MMB in the positional callout of the ID

and 4.8 if datum feature A is callout at LMB in the positional callout of the ID.

Pmarc,

Am I correct? Or I confuse the audience even more?

We are talking about a side-subject related with the original thread:

Your thread is here: (for a quick reference)

http://www.eng-tips.com/viewthread.cfm?qid=351570

THEN, going back to the OP original question

If “Kurlikovski” method is used, then

no needto subtract the form error on datum feature E: 10.5-10.0 = 0.5), as you will get it in the datum shift (B at MMB)If VC/ RC method is used then

you do needto take care of the form error and the non-requirement of the perfect form at LMC when x min is calculated.Enough said. I am waiting for the experts to chime in. Not sure I got this issue solved. I just hope.

## RE: VC and RC

Is the book: Tolerance Stack Self Study course? or else?

Link

## RE: VC and RC

Orange book in the link picture

It is the Tolerance Stack by Alex. K.

## RE: VC and RC

Allow me to answer your question (hopefully) by answering aniiben's question:

1. If the OD, datum feature A, is referenced at MMB, the minimum distance is 4.7.

2. If the OD, datum feature A, is referenced at LMB, the minimum distance is also 4.7.

"Why is that?", you may ask. It is because the size of LMB boundary of datum feature A is not 19.9, but 19.7.

## RE: VC and RC

Not sure I understand it at this point.

Are you saying that the perfect form at LMC is not required when the OD is at least material condition? Not sure where “It is because the size of LMB boundary of datum feature A is not 19.9, but 19.7” is coming from. Specially 19.7.

Let me recap a bit: (following your described cases)

OD: Datum feature A: Ø19.9 - 20.1

ID: Ø9.9 – 10.1,

Case 1: position Ø 0.2 LMC wrt A at LMB

Case 2: position Ø 0 MMC wrt A at LMB

Both of these cases will drive a minimum possible distance x min (between the OD and ID) of 4.7?

I get 4.8 no matter how I spin it.

Any help, maybe even “for a six years old child instructions” will be greatly appreciated.

I just want to say, it is a simple cylindrical part with a hole in it………”closed mind of the month” award is mine.

I think I need a vacation…..

## RE: VC and RC

For the 2B and 2S condition, the < indicates the column the MMC condition occurs, in this case, line F for the bonus shown on line D, and line A for the shift on line E.