Thru hole dimensioning in deep part 15

[Out0fSquare]

Really need help with this.

I have a cube that is eight inches square. There are four holes to be drilled through the entire depth of the part and the centerline of the holes are dimensioned only on the top view. The holes are 1/4" diameter. There is a drawing tolerance of +/- .010.

The hole pattern dimensioning uses no control boxes, neither does it have any requirement for perpendicularity, celindricity, parrellism, etc. All that is shown is the distance to the first hole from the part edges and the center-to-center location for the hole pattern.

The part was manufactured by a outside shop. Where the holes exit the part on the "bottom" they do not fall within the drawing tolerance as measured from the edges at the bottom of the cube.

I contend that the drawing does not control the exit hole locations and so our inspection department should not flag this as discrepant.

My question is this: What controls the exit hole tolerance for thru holes drilled through thick parts when the holes are dimensioned on a drawing only on the "entrance" view of the hole?

 

[fcsuper]

I would be cautious about the precident. Any arguement used to allow the acceptance of parts could give the manufacturer more ammo the next time, and that next time might be on something you personally are responsible for.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[ringman]

Ootofsquare

Again, I believe tthat without SOME STANDARD being stated in the documentation package, NONE will be applicable.

 

[meintsi]

Even if a standard was stated (as it should be on all drawings), you cannot assume perpendicularity for any hole axis.

According to ASME Y14.5, a feature control frame "True Postion" tolerance, when applied to to a cylindrical feature, correctly controls what some would expect in the situation, a perpendicualr hole. IT defines not only the starting point of the feature, it also adds feature axis control. [ASME Y14.5M-1994 Section 5.2]

Since the drawing is incomplete (and therefore technically incorrect), arguements for both sides in the case, because of the ambiguity, are allowed to happen.


Remember...
[navy]"If you don't use your head,[/navy]
[navy]your going to have to use your feet."[/navy]

 

[KENAT]

Mousetrap, ringman is correct, if you don't either reference a standard or explicitly explain on the drawing then it's ambiguous.

Most people will more or less interpret a drawing based on whatever standards or conventions they are used to if it doesn't explicitly state one. However, this doesn't make it correct to do so.

The drawing is ambiguous, while I'd expect it to mean what you say it means it's not explicit.


KENAT, probably the least qualified checker you'll ever meet...

 

[fcsuper]

meintsi, your statement is correct, but it doesn't really seem apply to Outofsquare's question (as I understand it) in the way you've stated. I agree that if perpendicularity is not called out, then it is not assumed. However, if the dimension is placed on that hole, that dimension stands for the whole feature, per ASME.

With no standard applied, he still has a tough sell because the drawing still communicates a specification. I actually would suggest the drawing is complete per the design intent, and the parts are out of spec because the dimension is understand by itself without the existance of a standard. It is a specification as to what is desired, regardless of how unrealistic that specification is. To say that no standard means no interpretation is silly. It's like saying we need state Webster Dictionary as our standard each and every time before we speak.

With that said, I would suggest the drawing is updated to state the ASME standard in order to apply GeoTols to that feature to allow for the variation they are observing in the part. (GeoTols are much more complex and even with a standard are open to interpretation, but contrast a simple dimension is common enough to be understood even by people outside the industry.)



Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[vc66]

No stated standard? Then the only thing that controls the "exit" hole (or entrance hole for that matter) is the the dimensions on the drawing that pertain to that feature, i.e. the size tolerance and the x-y tolerances of the hole located from the edges of the part. If you find that the "exit" hole is within the acceptable maximum stacked tolerance of those dimensions, then the part meets the drawing. If not, then it doesn't meet the drawing.

Whether that was the intent of the person who drew the drawing or not, is a different story. If it doesn't meet function--tough--he/she should've defined it better.

V

Mechanical Engineer
"When I am working on a problem, I do not think of beauty, but when I've finished, if the solution is not beautiful, I know it is wrong."

- R. Buckminster Fuller

 

[KENAT]

Without a standard stated, why do we assume that the dimension & tolerance apply all through the hole/to both entry & exit?

Now as I've hinted before, I'd make that assumption because that's what the standard I normally work to says, but if it came to court of law type situation I wouldn't put any money on it.

KENAT, probably the least qualified checker you'll ever meet...

 

[CheckerRon]

Ignoring all the tolerancing chatter and thinking from a manufacturing point of view, have you looked into gun drilling the holes?

 

[ringman]

I believe the part has been fabricated. the original question pertained to the inspection with regards to the dimensioning method on the drawing. MOST CERTAINLY, IMPROVEMENTS CAN AND SHOULD BE MADE ON THE DOCUMENTATION. But the problem remains on what to do with the existing part and how to inspect.

 

[meintsi]

There is no implied relationship between features in any standard. In addition, no standard puts a numerical valve on any allowance or tolerance. The standards only communicate the methods required to depict design intent.

It is when people fully understand that since there is no implied relationship between features that the need for additional geometric control becomes clear.

A diameter dimension shown on one surface is a "feature of size" and does not dictate how that feature is "drilled thru" in relationship to the block. Only that at every individual cross-section, it is within a defined limit of size.

In practicality, industry has found that a relaxation of the strict enforcement of the Taylor Principle (ASME Y14.5 Rule#1) is left to the discretion of inspection of alternate quality function. A micrometer check will not verify the perfect form at MMC.

KENAT hit this point above, because of the standards one is used to working with, people will make assumptions based upon them (see vc66's post), but as this drawing is described by the asker, it would still be IMHO technically made to print.

This could be one example of why the standards were written in the first place. To give people the tools to clearly define design intent.

Remember...
[navy]"If you don't use your head,[/navy]
[navy]your going to have to use your feet."[/navy]

 

[vc66]

So meintsi, what you're saying is that the hole size, and dimensions from the edges need to be defined on the drawing, at each singular cross-section through the entire hole if there is no standard?

I think that people rely too much on the letter of the law. Relying on there having been no drawing standard, to get you out of making a bad part, is asinine. Although I agree that standards are necessary to guide people, as a person who had worked in a machine shop before I got my degree, I can honestly say that any machinist who looks at a drawing with deep thru holes, and only measures on one side of the cube to check size and distance from the edges, is a careless machinist.

Neither the drawing creator nor the machinist are without fault, here. The drawing should've been defined better, and the machinist should've had the common sense to realize that the drawing was vague before making the part. In the end, common sense is just as important as drawing standards.

Keep in mind, this is all my two cents, and I don't mean to offend anyone.

V

Mechanical Engineer
"When I am working on a problem, I do not think of beauty, but when I've finished, if the solution is not beautiful, I know it is wrong."

- R. Buckminster Fuller

 

[fcsuper]

I obviously agree with vc66. I actually think Out0fSquare is actually trying to claim the drawing says something which is does not. The drawing is clear based on what Out0fSquare has stated. The hole must fall within the stated spec. What Out0fSquare is adding to the drawing is "this dimension only applies to the entry side of the hole". But the drawing itself doesn't say that. It only says "This thru hole is to be such and such distance from the edge" by having the dim. There's nothing implied. It is an absolute specification that even has a tolerance to its location.

The only open question for incoming inspection is how to determine the edge and hole hole surfaces, and how to measure there relationship. The only variable is in the measurement process itself, not in the specification.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[ewh]

As dimensioned, I would interpret is based on the tolerance information given. The entry points are defined, the axes direction is defined. If the entry points are correctly located and the axis is normal to the entry face within the angular tolerance (if there is one), then the part should pass regardless of the exit locations, even if functionally it is not a good part.

 

[fcsuper]

ewh, I think you are adding specification that isn't on the drawing by mentioning axes of direction. The specification actually has nothing to do with the surface upon which the hole starts, only the dimension from the edge surface to the center of the hole. .

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[ewh]

I agree that the axes have nothing to do with the start surface, other than both are defined by the view orientation. They ARE defined as being normal to the view, however, or the feature would not be circular, but elliptical. This is not per a specification, but simple geometry.

 

[vc66]

ewh, I understand what you are saying, but let me play devil's advocate. Say that we have the cube in question, and there is NO difference at all between any of the faces, and all the holes are drilled directly in the center of the faces of the cube. Now, I hope you'll agree that there are no "entry" and "exit" holes, here. What I may consider an exit hole, you may consider an entry hole. So, if the drill wanders from the "entry" point during machining, and you inspect it, it's good, because your choice of entry hole happens to be correct, but directly on the other side of the cube, I measure, and whaddya know? it's out of spec. This is why I would measure both sides, because I have no idea which side is which. If either side is out of tolerance, I assume that this is the "entry" side, and it's out of spec.

This is safe inspection. If this is a life saving device, and I just measure one of those sides, and that distance from the edge is critical to function, then it's better to be on the safe side and reject it, until I'm told it's OK by the design engineer, who couldn't be bothered stating a standard and calling out straightness and perpendicularity.

I obviously realize that a life saving device would be better-engineered, but you understand my point.

V

Mechanical Engineer
"When I am working on a problem, I do not think of beauty, but when I've finished, if the solution is not beautiful, I know it is wrong."

- R. Buckminster Fuller

 

[KENAT]

However, arguably the drawing only shows the holes to meet that tolerance/dimension on where they break one surface. If you measure it and it meets spec on one surface it's good right?

That's pretty much the root of the argument isn't it.

KENAT, probably the least qualified checker you'll ever meet...

 

[fcsuper]

ewh, in addition, as meintsi stated above, "there is no implied relationship between features in any standard." The have a tolerance you mentioned would require a GeoTol to establish the relationship between entry surface and the hole. With a datum and a control frame, their is no specification for such. A relationship cannot be assumed, even on a drawing view that is square to the part. The drawing view by its own right is no a specification, nor does it have tolerance to its orientation.

If ASME was mentioned on the drawing, 90deg angle is assumed for all unspecified angles. But if ASME is mention, this is actually a moot point because of paragraph 2.7.1.1, sited above. BTW, this is where meintsi's statement is wrong. ASME Y14.5M does imply a 90deg angle for unspecified angles.



Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[vc66]

Exactly, KENAT. In my example, which surface is that? If everything is literally symmetrical, how do we know which surface corresponds to the one on the drawing with the dimension?

Hence, I would check them all to be safe.

V

Mechanical Engineer
"When I am working on a problem, I do not think of beauty, but when I've finished, if the solution is not beautiful, I know it is wrong."

- R. Buckminster Fuller

 

[fcsuper]

KENAT, the surface of exit and entry are not part of the specification that Out0fSquare stated. As stated above, such a relationship could only be establish with GeoTols. The dimension as stated would be required the hole to be at the distance specified for infinity. The entry and exit cross sections are no different from each other or from any other cross section when it comes to whether or not the hole falls within the specification stated.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group