(A) Controls the axes of 4X 5.0 diameter holes within 4 parallelpiped tolerance zones (0.2 X 0.2, 10.0 deep) perpendicular to surface [A] and in a 32 X 32 square pattern.
(B) Controls the axes of 4X 5.0 diameter holes within 4 parallelpiped tolerance zones (0.2 X 0.2, 10.0 deep) perpendicular to surface [A] and in a 32 X 32 square pattern... that is displaced 9.0 from and 9.0 from [C].
WOW, that is a big part! 50" x 50" x 10" thk.
If that part is metric, read Y14.5, any edition.
Metric dimensions do NOT use trailing zero's!
The difference is that (B) has defined which edges to fixture the part from for inspection by defining the coordinate reference planes in all 3 directions.
In theroy they both are the same. The use of datum B and C is implied.
I haven't verified this, doing it from memeory, which means I could be totally wrong.
"Wildfires are dangerous, hard to control, and economically catastrophic."
Regarding trailing zero's, our company uses them to help indicate default tolerances.
X.X = +/- 0.30
X.XX = +/- 0.15
X.XXX = +/- 0.08
I will take you for your word on the Y14.5, I had a hard time going through it - extremely dry. Our titleblock and standard was from before my time, and I prefer it's use of the trailing zero.
Any other text books etc, even by committee members, still isn't "the standard". In some cases they may put their own flavour or preference etc. into it which isn't explicitly in the standard.
KENAT,
Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:
I have worked a number of places that used trailing zeros with metric dimensions to control tolerances. I would consider the title block tolerance or a similar note to take precidence over the no trailing zeros standard for metric dimensions. A defacto company standard.
Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services
The positional tolerance zone for a hole should be a cylindrical zone with diameter 0.2 X 10 long, so the position callout should have a diameter symbol before the tolerance.
The postion tolerance for a hole doesn't have to be a circular zone. If appropriate to function a rectangular tol zone is perfectly legitimate. There is no "should" about it, at most a "is normally".
KENAT,
Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:
The difference is that with (A) is that your hole pattern has no form control. With (B) it does. (A) is guaranteed to give you a hole pattern with targets that are out-of-square.
Here's why. The outer 50 x 50 square has no angular tolerance between the sides. Absent a note on the drawing, it's undefined. With (A), your target is 9 units and 41 units from a plane which contacts the high spots on datum feature B, and 9 and 41 units from a plane whith contacts the high spots on datum feature C. To the extent that those features may be mis-oriented with respect to each other (or to datum A), that's the misorientation you'll get in your hole pattern.
With (B) your targets vertically is 9 and 41 units from a plane which contacts the high spots on datum feature B and is perfectly oriented with respect to datum feature A. your targets horizontally are also 9 and 41 units from a plane which contacts the high spots (or spot) on datum feature C and is perfectly oriented with respect to datum feature A and datum feature B.
If your trying to match a mating part, you probably want (B) and not (A).
If a rectangular tol zone is the designer’s intent, then the print should specify the tol on both horizontal and vertical direction, otherwise the diameter symbol should be added.
Fair point, they're either missing an fcf or a dia sign.
I think somewhere I saw about it meaning a square zone withouth the dia symbol but what you say sounds familiar for 14.5, or is it only required if you want a 'rectangle' rather than square. I can't recall and this is a bit off topic.
KENAT,
Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:
The difference is that with (A) is that your hole pattern has no form control. With (B) it does. (A) is guaranteed to give you a hole pattern with targets that are out-of-square.
If the basics were changed to limit dimensions then your point has some merit.
By declaring the four holes a pattern with the "4X" designation... linked to a feature control frame... all four features have a basic pattern relationship to one another regardless of datum feature designations. When [A] is added to the FCF those tolerance zones are oriented to [A]... and when [A|B|C] is added those zones are oriented and located relative to the DRF established by [A|B|C].
Actually, Rule #1 gives form control based on the tolerance of size for either callout (based on the generic tolerances in the title block). The position control doesn't control form.
As indicated above, for it to be a linear tolerance, the dimension arrow across the feature (i.e. not radially) needs to show the direction. There is no expectation of a square zone just because the diameter symbol is missing. The absence of the direction indicator makes callout (A)illegal.
Otherwise, the two callouts (A) and (B) are in conflict, as (A) is not a refinement of (B); they both have the same tolerance of 0.2 on position (ignoring the preceding point about absence of diameter symbol), and both refer to the same four features. Thus, they are in conflict.
Now, if this was a graphic generated just to ask what the difference is between the two callouts (assuming the cylindrical tolerance zone in (A)), then ...
Callout (B) establishes the location in space (as related to the datums) at which each feature should theoretically be; this includes orientation to each of the datums, including Datum A.
Callout (A) establishes only the perpendicularity requirements of the axis wrt Datum A. As a result, the pattern of 4 holes (as established by the 4X) is free to float around as a group, maintaining general orientation and location wrt each other, but not to datums B or C.
You are correct, the image was a graphic that represents my "question". I did also forget the diameter symbol - was in a rush to get an answer quickly and omitted it accidentally.
I think it is clear;
A > gives an un-clocked/positioned pattern, but does keep the holes perpendicular to datum A
B > clocks and positions the pattern, while also keeping the pattern perpendicular to datum A
Yes, but not complete. "A" not only doesn't lock down rotation, but also doesn't provide a location in space either, as "B" and "C" aren't referenced in the FCF.
At one company, we stated on the drawing that it complied with ANSI Y-14.5m-1982, then updated to ASME Y14.5m-1994. We also used trailing zeros. When I started there, I pointed this out since you can't have both. Either the drawing complies or it doesn't! Most CAd systems have to forced to put trailing zeros when doing netric standard drawings.
The obvious reason to conform to the standard is when handed a drawing, you don't have to search to see what the units are. If you see trailing zeros, then it is in inches. If you see leading zeros or no trailing zeros then it is a metric part.
"Wildfires are dangerous, hard to control, and economically catastrophic."
