Basic bolt circle diameter dim. Does it control bolt pattern runout to a center? 1

[mschroeder]

I have a flat disk, 20 holes around, and see so many examples of bolt circle dia's dimensioned as basic with a position on the holes.

Does the basic bolt circle dimension control location to a center hole in the disk used as datum A?

Does the basic bolt circle diameter dimension still allow circular position tolerance zones or are they now constrained to arc shaped zones?

Thanks.

--mschroeder

 

[dgallup]

1) It does if you have Datum A in your position call out as a datum.
2) It does if you have a diameter symbol before the tolerance in your position call out.

Kind of hard to be more specific since you did not post a pic.

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[mschroeder]

Here's an image representing the situation.
Thanks for the reply.

 

[pmarc]

Basic dia. 4.875 defines ideal circle perfectly centered on datum axis A that centers of all positional tolerance centers must be on. Positional tolerance zones are always circular (or being more precise - cylindrical) -- it is because there is a diameter symbol in front of .010 value in feature control frame. The fact that pattern of holes is not constrained in rotation to datum axis A does not mean that the tolerance zones ever become arc-shaped.

Side note: Currently the pattern of 20 holes is not tied in rotation to 3 arc-shaped holes in the center. If such relationship is required the print must specify this.

 

[powerhound]

To expand on pmarc's comment: the 11 degree dimension does absolutely nothing. What is that hole 11 degrees from? It does not tie the arc shaped pattern to the hole pattern although I have a sneaking suspicion that someone thinks it does. Other than that, yes, your 20-hole pattern is related to the center of the ID hole and your tolerance zones are cylindrical, not arc shaped.

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[CheckerHater]

I wouldn’t be so sure that “the pattern of 20 holes is not tied in rotation to 3 arc-shaped holes in the center”

First, we cannot see Detail view A which supposedly clarifies position of sausage-shaped slots.

Second, if position of slots is controlled by GD&T as well, vertical axis going thru upper sausage and horizontal axis tied to 11 deg. basic dimension have implied basic 90 deg. dimension between them.

I would be more worried about adding flat part surface as primary datum.

 

[powerhound]

Good point CH. I suppose if in another view the slots were located with respect to datum A then simultaneous requirements would kick in. I don't, however, see what you're saying about the implied 90 rule. It says that features shown at 90 degrees to each other are implied a basic 90. Unless this could be a dreaded extension of principle, there is no feature that is 90 degrees to the upper sausage so I don't think it applied in this case. I could be wrong so I'll wait to see what others think.

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[CheckerHater]

I believe it applies to axis as well as to features, so if the feature is sitting on the axis – here you go.

 

[powerhound]

CH,

Well, you pretty much redrew the same scenario as in the OP. Was I supposed to see it any differently? Your depiction of what you call "real" is, in fact, implied if you go by YOUR interpretation of the fundamental rule. What would be "real" would be an angle from the hole at 90 degrees to the hole at 160 degrees. Believe me when I say I'm perfectly okay with extensions of principle when they are supported but I don't see where it's permissible to imply an angle from anything but a feature. Your 20 degree angle does not originate from a feature and neither does the 11 degree angle from the OP. Read the fundamental rules and see that in both cases (i and j) any 90 degree implication requires features.

Powerhound, GDTP S-0731
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Inventor 2013
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[pmarc]

If detail view A defines location of 3 slots to datum axis A, the slots will be tied in rotation with the pattern of 20 holes due to simultaneous requirement rule. However, in order to have this relationship fully defined, at least one of the slots must have basic angular relationship to horizontal axis of the part defined or to any of the pattern holes (the second option for sure will not be visible in detail view A). If it is the basic angle to horizontal axis, basic 11 degrees dimension will do the rest.

As for implied basic 90 degrees angle between slots and holes -- sorry, but I do not see how this could apply here.

As for a need of planar primary datum feature, I fully agree - it is needed. However it does not necessarily have to be one of 2 flat surfaces of the part, but a center plane derived from part's thickness as well.

 

[CheckerHater]

Powerhound, pmarc,

When I called the dimension “real” vs. “implied” I only meant that dimension actually is present on the drawing as opposed to the one we imagine to be there.

Para. 2.1.1.4 states in plain English:
“Where center lines and surfaces are depicted on 2D orthographic engineering drawings intersecting at right angles or parallel to each other and basic dimensions or geometric tolerances have been specified, implied 90 deg or 0 deg. basic angles are understood to apply.”
It does say ABSOLUTELY NOTHING about holes being associated with said center lines. So in my interpretation just center lines alone are good enough.

pmarc,

How about implied 0 deg. between top slot and vertical axis?

 

[CheckerHater]

Just in case you guys are having problem with “intentionally incomplete” drawings, I am trying to show in finer detail how presence of properly toleranced slot will change the game.

Do you still believe that we must place basic 90 deg. dimension on the drawing, or is it somehow implied?

 

[mschroeder]

Thanks gang--

FYI the 11 degree dim to horizontal was there to tie three sets of smaller bolt circle patterns to each other rotationally and I neglected to omit it for my simplified image.

--mschroeder

 

[powerhound]

CH,

You misquoted 2.1.1.3. Please re-post it without leaving out the functional word.

Powerhound, GDTP S-0731
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[powerhound]

I guess that was just an "intentionally incomplete" paragraph quotation...

Powerhound, GDTP S-0731
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[CheckerHater]

Powerhound,

First, it’s 2.1.1.4

Second, this is exactly how it looks in my copy of ASME Y14.5-2009

Third, when you are calling somebody a liar, it is your job to provide the evidence.

 

[powerhound]

Sorry CH, I wasn't calling you a liar. I was just playing off of your "intentionally incomplete" post. I'm sorry you took it that way.

Powerhound, GDTP S-0731
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Inventor 2013
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Taji, Iraq OIF II

 

[CheckerHater]

I keep searching for missed word…

 

[powerhound]

Look at 2.1.1.3. and compare it to 2.1.1.4. The operational word is "features". Admittedly, I read the wrong paragraph.

My problem with this entire thing is that the way the centerline is used does not depict a part feature. The only features a centerline depicts are an axis or centerplane. I've always related features to other features. Paragraph 2.1.1.4 is not in the 94 standard but 2.1.1.3 is, although it's actually 2.1.1.2 in that standard. Maybe the committee decided to give centerlines more power. I don't understand why though. You can't touch them to measure from them, you can only use features that establish them to measure from. Since in your "incomplete" and "more complete" drawings you have an upper feature to relate to, you're still not relating the hole in question to the 180 degree line, you still have to relate back to the feature at 90 degrees. I know you are just trying to illustrate a point but at what point does it become a better idea to relate a feature to something that can't be touched than to something that can? This is why I don't think that was the intent of the paragraph we are talking about. I'm sure if you were actually making that drawing for production, you would have related one feature to the other via a 70 degree basic angle.







Powerhound, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[CheckerHater]

OK, now I understand. I only have a copy of 2009 book, so I don’t have a chance to roll back and compare.
Looks like it’s not the first example of Y14 making small adjustment that change the meaning greatly.
About centerlines – we still dimension to the center of the hole, right? Maybe things are not so bad.
I possibly over-reacted, but put yourself in my place – I quoted the sentence down to the letter, so I didn’t feel like I deserved such treatment.