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Position Tolerance of a square feature on a disk

Position Tolerance of a square feature on a disk

Position Tolerance of a square feature on a disk

(OP)
I have a disk that is inserted in a cylinder. A square sleeve will be inserted and welded to the square bore of the disk and I am trying to center the hole on the disk. Is a position tolerance the best way to do this? I have read that you can use position with any feature, not just a circle. Even though it is a square, the diameter callout still seems correct to me as the tolerance zone.

Otherwise, setting an X-Y tolerance on the distance to the centerline would give a similar result. I guess the only difference there is the square vs circular tolerance zone.

Is this correct? Thank you.

http://files.engineering.com/getfile.aspx?folder=9...
http://files.engineering.com/getfile.aspx?folder=7...

RE: Position Tolerance of a square feature on a disk

Yes, a circular tolerance zone of Ø.030 would be appropriate given the tolerances you show.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

RE: Position Tolerance of a square feature on a disk

ewh -- what is it that we want to fall within that diametrical zone?

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: Position Tolerance of a square feature on a disk

Derived axis/center of a square. Or better we use Concentricity?

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

RE: Position Tolerance of a square feature on a disk

Hi All,

I believe what John-Paul is getting at is how to deal with the form error on part surfaces:



On the irregular hole shown, several different derived axes/centers are possible (as well as several different centerlines for the OD). Given the tight tolerances, the magnitude of the irregularities could be in the same ballpark as the tolerances.

I'm also wondering - why is the location tolerance for this hole so tight, if a square sleeve is going to be welded into it?

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Position Tolerance of a square feature on a disk

If I remember correctly, axis is derived from mating envelope and not the actual surface.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

RE: Position Tolerance of a square feature on a disk

Yes, I realize that an axis is derived from UAME, so form wasn't the issue. (Thanks anyhow, Evan!)

But ... what is the axis? The center of the AME from the vertical walls and then the center of the AME from the horizontal walls, then taking the intersection of those two planes? Or maybe a perfect square that expands until it hits, what, 3 points? (This seems to be an "irregular feature of size" if I can throw that term in here.)

The standard would normally say in a instance like this to default to the boundary interpretation. Yet the OP doesn't want that because the thing has to be centered in a circular fashion.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: Position Tolerance of a square feature on a disk

Another funny question: how to produce two-directional tolerance zone (if there is no other choice) based on one single round datum feature?

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

RE: Position Tolerance of a square feature on a disk

If I can safely assume the usage of the part (big IF) I would say it would be the center point of the biggest perfect square that fits in the square hole. How to accurately convey that through appropriate language, though, I would have to think about more.

RE: Position Tolerance of a square feature on a disk

(OP)
All excellent points, and I will answer what I can. This is a very simplified example of the actual part. We currently use a round sleeve but have had years of problems and I am now looking at a square sleeve. I have a few options, but I need to at least get this one quoted. We did have problems when the circular sleeve was not centered and the shaft would move and cause failures. I need that shaft to be as centered on that disk as possible.

There will be a chamfer on the square bore, and on the sleeve, and that is where it will be welded (currently only on one side of the disk).

We currently have a +.002" -.000" tolerance on the circular bore and a +.000 - .005" tolerance on the circular sleeve, so yes, pretty tight tolerances.

Measuring these tolerances relative to the OD seems tough to me as well. The real OD of this part is about 2'.

JNieman, that sounds like my end goal, but all relative to the OD. And yes, I am struggling to come up with best way to convey this.

RE: Position Tolerance of a square feature on a disk

Sounds like a job for concentricity of the square relative to the OD.

Or locate the OD relative to each width of the square.

RE: Position Tolerance of a square feature on a disk

Hi Jdmmech,

Can you explain the working of this assembly?
Just wanted to know whether concentricity between disc and sleeve is more important or perpendicularity between sleeve and disc face.

RE: Position Tolerance of a square feature on a disk

CH,

I'm not sure that your latest possibility works:
-The two directly toleranced width dimensions are not compatible with the profile tolerance (the dimensions should be basic)
-The position tolerance would only apply to one of the widths. I think it would need another position tolerance for the other width.

This gets into several gray areas. I'm not sure what happens when a position tolerance referenced RFS is applied to a width that is controlled by a profile tolerance. It's defined when referenced MMC, using the boundary position concepts, but I'm not sure about RFS.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Position Tolerance of a square feature on a disk

Evan,

2X applies to both dimension and position. The frame can be moved to the right to make it more obvious, but it won't really change the meaning.

The square has 4 implied basic 90 deg angles and profile controls orientation of square sides to each other.

No, dimensions shouldn't be basic. No, the width is not controlled by profile tolerance.
In fact, when you see profile applied to feature without basic dimensions, it is clear indication that profile controls form or/and orientation.

RE: Position Tolerance of a square feature on a disk

CH -- you clearly made the profile "all around." So the width is being controlled by the profile tol. Thus, the dims have to be basic.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: Position Tolerance of a square feature on a disk

Sorry JP, but I see it the other way "around".

I don't specify "true" outline - I don't control "true" outline. But if you see it as possible ambiguity, what will happen if I replace "all around" with 4X ?

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

RE: Position Tolerance of a square feature on a disk

CH -- profile must be applied to a "true profile" per paragraph 8.2. But see other thread I'm starting for this off-shoot topic.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: Position Tolerance of a square feature on a disk

Just to put a bow on this...
Based on the other thread, we've apparently established that the size dims of this square slot do not have to be basic dims, even though there is a profile tolerance all around, right?

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: Position Tolerance of a square feature on a disk

JP,

Well, I guess we agreed that there is no "absolute" requirement to always have basic dimensions associated with profile.
We also found out that the concept may be confusing for many people.

If we agree that profile can be used to control form, orientation, but not the size, what do you think would be the best way to do so?
It's not a trick question or attempt to start another war.

If we believe something may be right, but confusing, the natural thing to do is to look for better way.
Hense my question from Dec. 1 about only using "4X"

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

RE: Position Tolerance of a square feature on a disk

I was kinda sure that an "all-around" profile would need basic dims. That's why I started the other thread. But you and others made the case that the standard doesn't really require that, so I backed down.

With that in mind, this example of the square slot with all-around profile and non-basic dims seems to be legal per Y14.5. But I still don't have to like it :)

As for your question, yes it does seem to be the only way to control form/orientation but not size for an unusual shape.


John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: Position Tolerance of a square feature on a disk

I don't see the jump to applying profile to this case. The control is for deviation from a true profile and this hasn't got one, though I see the confusion where there is a reference to refining features controlled by size dimensions. However, the example I see in the standard is for a truncated cone, which hasn't got a size dimension. Instead it is a compound of a location dimension and a local size dimension. Since the two are interdependent it isn't -a- size dimension. It's more like the two dimensions that can be used for a chamfer. Delete either one and the notion of size goes away.

RE: Position Tolerance of a square feature on a disk

Dave, Fig. 8-18 in the standard does indeed have a size location. This is because the local size you speak of is anchored to datum B (whereas in Fig. 8-17 it floats since there are no datum references, so I might agree with you there). So if we say that profile can be used in Fig. 8-18 with a non-basic dim defining the true profile, then there is nothing in Y14.5 to say that this example of the square slot is incorrect.

Also, feel free to weigh in on the other thread ("must profile be applied to a basic profile?").

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: Position Tolerance of a square feature on a disk

The reason I say it is compound is that the cone is guaranteed to have a given size at some axial location, and it will have some size at a given location at an arbitrary distance along the axis. As such neither dimension is stand-alone and is a compound dimension that is neither size nor location.

Without datum B the form and radial location tolerance of the cone is still defined; what the diameter tolerance changes is the axial location of the flat relative to the cone apex. As such, the profile tolerance does not refine the diameter control at that location.

RE: Position Tolerance of a square feature on a disk

I'm with 3DDave here. I don't think the secondary datum reference of the profile tolerance has any effect at all in Fig. 8-18. Without a complete basic relationship to datum B, the profile tolerance zone can float axially (as in Fig. 8-27). Without a fixed axial reference, size has no meaning for the cone.

- pylfrm

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