Standard Practice for Centering a Hole 4

[JoeC.]

I have an issue of figuring out what the best way to dimension this type of drawing would be.

If I have a hole in a middle of a rectangle, which I don't really care much about it's total width (say 10+-1), but I do want the hole to be in the center of the that rectangle regardless of how big or small it is within a tolerance of +-0.1.

How do I go about giving dimensions so that the hole is still centered regardless of the rectangle width?

 

[cr7]

Like this maybe?

 

[Belanger]

Just a quick thing first... If that hole creates datum A, then wouldn't you want the outside edges of the part dimensioned from the hole? In other words, is the hole the driving factor, or the driven factor?

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

 

[ctopher]

cr7,
I like how you used datums "G,D,T".

ctopher, CSWP
SolidWorks '17
ctophers home
SolidWorks Legion

 

[chez311]

Ditto JP - additionally we typically want our datum features to be sufficiently more precise than the features they control and you've applied a very loose tolerance on the size of the width.

 

[JoeC.]

Thanks for the quick responses. What exactly would be the dimension from D if I want it to be centered? If I put 5+-0.1 would that not be affected if total length is 11? How exactly do I state that it is centered? or would it be implied and understood in such a case?

 

[JoeC.]

Also I just wasn't entirely sure where the datums should go which is why I chose the hole for A. It made sense because I don't care about the accuracy of that width but I care more about the hole being centered.

 

[JoeC.]

I simply created this part with these dimensions to figure out if it is possible to get a hole in the center of a rectangle within a tight tolerance if the rectangle's length dimension is of no importance, but what's important is that the hole is centered. My issue is the understanding of centerlines and how I can imply in GD&T that I care about centering a hole even if the total length is not of importance

 

[cr7]

If I put 5+-0.1...

don't do that. For true position you need basic dimensions,

or would it be implied...

I think yes, but I'm no expert. It could also depend on standard. ISO or ASME?

 

[cr7]

JoeC. you probably want to use the diameter simbol also:

 

[JoeC.]

Using Y14.5 If I add a centerline, would that be clear that I desire the hole to be centered? and if so, how do I make it clear that the centerline is between the two sides I want without dimensioning it to keep it basic

 

[chez311]

JoeC,

Center lines are only a means of either explicitly (through a dimension directly to the center line) or implicitly (ie: through implied zero basic distance between two center lines/planes) dimensioning a feature. They do not by themselves create any sort of control or tolerance zone - ie: a feature fully defined with basic dimensions and a centerline but without a position (or similar) tolerance would be of little use.

As far as the implied use of center lines/planes see this discussion:

https://www.eng-tips.com/viewthread.cfm?qid=464639

I see that this is only a theoretical part, therefore I won't read into your requirements for how the part should function/mate however I will reiterate - typically we want our datum features to be sufficiently more accurate than the features which it controls, especially since there is no form control on the width. It would seem to me that one would want to derive the position of the width from the hole not the other way around. Regardless - RFS position controls the derived axis/center plane of a hole/width within a tolerance zone located at true position. It will do approximately what you are asking. If true "symmetry" is desired in Y14.5-2009 a symmetry control could be applied to the width, or in Y14.5-2018 (symmetry/concentricity have been removed) something similar could be accomplished with a combination of basic dimensions/profile/dynamic profile.

 

[JoeC.]

Thanks a lot for the responses. That clarified my misunderstanding, also the link was very helpful.

 

[Burunduk]

If you want a relatively accurate centering between a hole and a loose-tolerance width, then as others mentioned, a tolerance of position RFS on the width referencing the hole as a datum feature might be the better solution. If for the sake of an academic exercise you want to do that the other way around (the width being the datum feature) it is possible too, however, make sure you have some form and mutual orientation control on the parallel faces of the width feature. With a tolerance as loose as +/-1, according to Rule #1 of Y14.5, you may have form error of up to 2 mm on each of the faces if no form or orientation controls are specified. This may lead to a not very good datum feature, resulting in an unreliable and unrepeatable datum center plane setting the location of the hole's tolerance zone.

 

[3DDave]

I would not choose D as the second datum feature; T makes more sense because it has a higher extent to dimension ratio.

 

[3DDave]

Also, the OP needs to buy and read their own copy of the Dimensioning and Tolerancing standard that applies to the drawings they are making.

 

[dgallup]

This is an excellent example where symmetry would be useful. I've never understood why symmetry is so out of favor. Is it even in the current standard?

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[Burunduk]

dgallup, symmetry and concentricity are out of the 2018 std.
What makes it favorable in this example?
How do you suggest to apply it here (what's the datum and what's the controlled feature)?

 

[cr7]

I would not choose D as the second datum feature; T makes more sense because it has a higher extent to dimension ratio.

Nice catch, my bad. BUT, it could depend on application. Otherwise I agree with you.

 

[cr7]

, symmetry and concentricity are out of the 2018 std.

Good to know, thanks.