True position callout 3

[uptick]

Hi there,
I need your opinion on the case below:
Problem: A buterfly valve with a shaft goes thru both side of the wall. Each side has a bearing bore callout.
1. The hole for the shaft is a thru hole with diameter A +/- tol with a datum A callout.
2. The bearing bore on the right states 2 X diameter +/- tol (for two bearings bores) with a datum B and a TP of .002" to datum A.
3. They call out a datum C on the bearing bore on the left of the body with a TP of .003" to datum B-C.
Question:
a. Is the callout in item 3 above valid? and good control?
b. Does the 2X diameter +/- tol with a TP of .002" to datum A in item 2 above apply to both bearing bores, regardless the callout in item 3 above? In other word, the callout in item 3 above is NOT REQUIRED.
Your earliest help is appeciated.
Uptick.

 

[PeterStock]

A sketch would help, but I am thinking you are correct. Is there a different diameter that could be the other surface for the 2X?

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net

 

[uptick]

Thanks PeterStock. Here is the sketch. I just want to know if the callout is correct? or do we really need datum C & the TP of .003" to B-C?
Your opinion would be appreciated.
Uptick.

 

[uptick]

One more try. Sketch is attached

 

[pmarc]

uptick,

1. As long as dia.002 position tolerance value relative to A is acceptable for you for both counterbores (C/B), you do not need callout in item 3 at all. By putting 2X next to the size of C/B you have clearly stated that |pos|dia.002|A| applies to both C/B's.

2. I have additional comment to a feature assigned as datum feature A 'THRU HOLE'. If your intention is to keep 2 parts of this hole coaxial, THRU HOLE note will not do this. It only implies coaxiality, however doesn't say what is the allowable tolerance for it. So in extreme situation left and right holes can be completely shifted in vertical direction and the valve will meet drawing requirements.

There are some methods in ASME Y14.5 std. of establishing coaxiality of interrupted features assigned as datum features:
- you could use CF (continuous feature) symbol, which is quite new concept, but makes two or more features of size as a single one. (See fig. 2-9 in Y14.5-2009)
- or you could apply 0 position tolerance at MMC without any datum reference to .402-.406 dim., which will also work in similar way. (See fig. 4-24 in Y14.5-2009)

 

[PaulJackson]

I imagine that the shaft has clearance to the thru bore diameter [A] as the valve functions... are there an O-ring seals that contact the shaft or are the bearings sealed or end caps do the sealing?

My guess is that [B-C] is the functional primary and CF [A] size and position devation would establish the boundaries for the seal pinch variation if there were O-rings between the bore and the shaft.

Paul

 

[fsincox]

uptick,
I work on valves identical to the ones you are showing, do we work together? While the through hole will most likely come first in processing, I do not necessarily feel obligated to mirror that in my callouts, in fact, I would reverse the order and call out the through hole at MMC to the bearing bore line (B-C). Either way the "thru hole" can take advantage of MMC.
Frank

 

[fsincox]

to the OP, is the call out valid technically, yes you can call out (2) bores to a common boreline (B-C). Is it what you want I don't know.
Is the 2X call out good enough? well could be. is the "thru hole" just a clearance hole for the shaft or are there seals on it of some sort?
Frank

 

[uptick]

Thanks everyone for the comeback.
A> pmarc: So the 2X on the B datum side with the TP callout will cover the other bore (other side)without repeat another TP callout? Y/N? Let assume that the drawing with the same callout as the sketch has already been released, questions:
1. How to check (inspect) the part as B-C?
2. What if the hole at datum C is away from datum B (let say .020" off of B), part may meet the requirement .003" to B-C, but will not work for the shaft installment. Am I right?

B> fsincox: I have seen the use of runout & cylindricity on B-C, but not TP. So the question is asked.

 

[fsincox]

Yes, of course, technically as wriiten the TP would cover the other bore, too. I would add, the callout as written makes datum "B" both bores or the common axis. The notation should be changed to avoid confusion if it is not intended that way.
I am going to assume you mean concentricity not cylindricity as no datum references are allowed in cylindricity.
TP to a common datum axis is used in the standard itself, Ref FIG 4.19, ASME Y14.5M-1994, pg. 67. It does not mean it is right for your application. I would also point out that if your numbers are taken literally, the second callout adds no value as .002 is smaller than .003.
Frank

 

[uptick]

fsincox,
I have a page (pg 5-117) from Global Engineering Document, tenth edition 2000, dimensions & tolerances where it has both run out & cylindricity callout. Datum A-B where one is to itself. See attachment.

My previous question is the TP to B-C where C is itself.

 

[fsincox]

uptick,
Chicago area?
OK, Thank you for your illustration, the cylindricity from the book references no datum and is applied correctly.
I would also agree that the TP shown on datum C seems misapplied, specifically, due to it's value. You are asking is it correct that involves a whole lot of questions.
First, I believe it is acceptable to derive a common axis from multiple coaxial features of size (preferably, no more than two) and hold other features including the feature(s) themselves to it using either TP, runout or concentricity. I chose to ignore multiple other issures in my first post, like the datums being incorrectly applied and mismatched as I understand it is just for illustration. However, in the end many times it is the details that may make an applicaton correct or not. So is the question can it be done or is the picture as given right?
My opinion:
Yes, it can be done if there was a good reason to and the numbers support that, say, as a refinement (smaller number) on both bores.
No, the picture is not right.
Frank

 

[uptick]

Unless I miss reading the posts, I have not seen a direct answer to the question I posted . Per the sketch I sent earlier, my question really is:
1. Can the hole in the left completely shifted vertically from datum B, but still meet pos|dia.00x|B-C| as required?
2. How to correctly establish the B-C for other measurement?

Need to learn. Thanks.

 

[fsincox]

Larry,
1. Can the hole in the left completely shifted vertically from datum B, but still meet pos|dia.00x|B-C| as required?

Completely? Well only within .002 max. I agree the B-C statement as written in your illustration adds no value, that is not the same as agreeing it is an incorrect statement, around here we must be careful.

2. How to correctly establish the B-C for other measurement?

I was hoping someone else would handle this as I am not an inspector. You can roughly calculate it if you can measure the location of bores themselves, there are machines that are designed to do his specifically if you need it all of the time, or use a CMM.
Frank