Datum with flatness and position tolerance specified?

[LITTLEMAN3]

I have a print with a leader line going to a surface. The line has a datum attached to it. There is also a flatness of .090 attached to the line. Then there is tolerance of .045 from the leader line to a line that is located away from the surface of the part. There is another tolerance of .090 with the leader line centered in the tolerance zone. There are multiple part dimensions running off the leader line. If we meet the flatness requirement what do the .045 and .090 tolerances around the leader line mean?

 

[PeterStock]

Could you post a sketch?

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net

http://www.linkedin.com/profile/view?id=30064526&trk=tab_pro

 

[drawoh]

LITTLEMAN3,

It would be nice to see a sketch.

Attaching an arrow to a surface with a datum and a flatness specification is no problem. If you attach a positional tolerance, you may have problems.

[ol]
[li]The positional tolerance must located from an existing datum. The datum attached to your face cannot be a primary one. There is no problem if it secondary or tertiary.[/li]
[li]Positional tolerances are used to locate features of size. Your surface does not sound like one. A profile tolerance would be more appropriate, with the limitations noted above.[/li]
[/ol]

JHG

 

[LITTLEMAN3]

See attached sketch. Thank you.

 

[PeterStock]

I think the intent is to show a bilateral profile tolerance. As the flatness and the "profile" tolerance are the same I think the .045 and .090 dimensions are redundant.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net

http://www.linkedin.com/profile/view?id=30064526&trk=tab_pro

 

[KENAT]

What drawing standard is this to?

I'd guess Peter may be right.

It seems like the .045 & .090 dimensions might be redundant but I'm not sure what they're trying to do.

Posting guidelines faq731-376

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

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

 

[pmarc]

This indeed looks like someone tried to define something similar to equal bilateral profile of surface callout.
Assuming Y14.5 (1994 or 2009 edition) is in charge on this drawing, I would not only say they are redudant but they are illegal. Flatness callout shall not be refined by such dimensions depicting tolerance zone distribution.

However I have no idea what was acceptable in previous editions of Y14.5 (1973, 1982), and looking at datum feature symbol BB one of these earlier issues may apply here.

 

[CheckerHater]

Looks like "old" Y14.5 or MIL-STD; the datum symbol goes as far back as 1953.

In the worst case scenario Flatness may be refinement of Parellelism, which in turn could be refinement of General tolerance (if Profile not used) with tolerance zones "floating" within each other.
So, the drawing could be emphasizing the fact, that tolerance zone is symmetrical about thru basic profile "no matter what".
Impossibe to tell without seeing how rest of the part is dimensioned; and reference to standard number wouldn't hurt

 

[drawoh]

LITTLEMAN3,

It looks to me like the drafter is trying to define the median (???) surface as datum. ASME Y14.5M-1994 defines the datum as the plane defined by the three points that contact the reference surface. This definitely would be off on the left side of your view.

The ASME standard is sensible, and fixturable. Can you ask the original drafter to show you a fixture that will pick up his datum face?

If you are allowed to redraw this thing, I suggest datum targets.

JHG