COUNTERBORE 7

[WHITMIREGT]

Hi everyone. I submitted this question August 28 and only had one
response. Let me reword the question. Figure 5-37 in the standard for
positioning a through hole and a counterbore hole with one positional
control. The question is, does the through hole and the cbore hole have
two different zones with the same tolerance size where the cbore hole
can tilt or shift in a different direction than the through hole, or
the two diameters must have one axis within one zone for the length of
both features?

 

[WHITMIREGT]

please ignore the August 28th date. It was from a different memo. I do not know how to delete the statement.

 

[ringman]

Gary,

Perhaps the committee violated one of its FUNDAMENTAL rules here in specifying a manufacturing process. Perhaps the proper way would have been to specify the diameters individually with the tolerancing as required to provide the proper clearnaces for the head and the body of the screw.

But as far as the example goes, I would have to go with a single tolerance zone for both features simultaneously.

 

[PaulJackson]

They are two individual features therefore an axis can be constructed for each feature independently.

 

[powerhound]

The axes of the two features must fall within the same tolerance zone but they are independent of each other. Reading 5.7(a) on page 135 it says "Identical diameter tolerance zones for hole and counterbore are coaxially located at true position relative to the specified datums". This is a clear indicator that the tolerance zones, although identical, are separate.
ringman,
I don't see where there is a manufacturing process specified. What am I missing?


Powerhound
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[ringman]

I have always thought that Cbore was manufacturing process which required the use of a Counterbore (tool) . Would that not be specifying the process rather than the geometric definition?

 

[ctopher]

I would make one callout for the hole and CBore, and one FCF for it. Treat them as one. It would be up to the machine shop if they want to machine them separate, but within the tol indicated.

Chris
SolidWorks 07 4.0/PDMWorks 07
AutoCAD 06
ctopher's home (updated 04-21-07)

 

[dingy2]

I agree that we have 2 features with the same tolerance and are independent of each other.

Dave D.

http://www.qmsi.ca

 

[KENAT]

My understanding was as majority of posters and as detailed by Power Hound.

That said this often seems to be overlooked by others, many assume the Cbore & hole are automatically co-axial, this includes people that prepare standard hole charts etc.

My checker actually went through a hole chart we'd been using and made this correction. Of course now I'm not sure they match standard C'bore tools, sometimes you can't win!

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

 

[powerhound]

ringman,
Counterbore is what the feature is called, like countersink or counterdrill. The tool and the process may share the same name, but the feature is what is being referred to in the standard. They don't care how you apply the counterbore, it just needs to be there. On a CNC mill, I never use a counterbore tool to apply a counterbore, I interpolate the larger diameter with an end mill.

Powerhound
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[WHITMIREGT]

As of this date, it is 5 to 1 in favor two separate axes.

It is my opinion, one axis for the length of both features:

1. Figure 5-37 states 0.25 positional tolerance zone for hole and counterbore. Not zones.

2. It does not make sense to have two axis going in two directions.

3. I think it implies one tool and one axis the total length of both features.

4. If the workpiece cost thousands and the two features were machined separately at different angles within the 0.25 zones with no assembly there would be litigation.

5. The bottom line is to state on the drawing next to the position callout the intended definition.

Gary

 

[PaulJackson]

So one might say "You can lead a horse to water, but you can't make him drink"

 

[KENAT]

Given your background Gary (assuming you're the Gary Whitmire I think you are as in Genium & Drafting Zone, 14.5 commitee member...) I'm loathed to disagree but...

1. In this case the figure doesn't quite appear to match the paragraph. 5.7a explicitly states 'zones'. Given what paragraph 1.1.4 says about the figures only being illustrations etc then I assume the wording in the paragraph takes priority.

2. Within the limits imposed by the pos tol, why not? If as Powerhound details above the c'bore is made by a second operation the axis could be off slightly from 'perfect' however, so long as the resulting feature is still in tolerance, and was correctly toleranced in the first place, it would still work.

3. Wouldn't implying one tool contravene 1.4e as ringman points out.

4. I thought positional gives some control over the angle of the feature (figure 5-6). Hence if toleranced correctly in the first place then if the holes are in tolerance it shouldn't prevent assembly.

5. To my understanding by referencing ASME Y14.5M-1994 on the drawing and dimensioning as paragraph 5.7a then additional clarification shouldn't be required. By stating next to the drawing do you mean dimensioning as per 5.7c?

(Just to clarify I'm looking at ASME Y14.5M-1994)

I hope these counterpoints are taken in the spirit they were made. Obviously this type of discussion can be healthy as it can lead to clarification of the standard or improved interpretation of it.

Ken

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

 

[ringman]

If the term Cbore were eliminated, and the holes were adequately defined and located by datum features and positional tolerances would we be having this discussion?

Is the current practice to specify drill, ream, or punch for holes?

 

[PaulJackson]

To be fair Gary, I think that if one has the luxury of using a stepped tool to do both the hole and the counter bore simultaneously that may be ideal for process efficiency when both features have similar tolerances for size, finish, orientation, and location. The standard however, in defining how multiple coaxial attributes "features" that can be specified for location or orientatation with a single FCF for the sake of reducing "clutter" on the drawing.... is not suggesting how those features are processed. The following paragraphs in the standard state that when the tolerances ar not similar more FCF's are required.

Also to be fair it is exceedingly difficult to create a stable and repeatable axis from a shallow counter bore without making huge assumptions about its orientation... so the axis, if checked for its displacement, is either generally assumed oriented to the axis of the deeper hole or assumed perpendicular to the datum feature.

All this considered... the liberties and constraints in the standard regard the features independently and make no inferences about processing.

 

[powerhound]

1. The paragraph that I cited specifically says "zones".
2. It doesn't make sense to have the axes of the two features mis-aligned either but they are going to be, no matter how hard you try. The amount of mis-alignment that is permissible is up to the designer to determine.
3. Nothing implies the use of a single tool.
4. If the part is out of tolerance there SHOULD be litigation regardless of whether the part cost hundreds, thousands, or millions. If not, there shouldn't. If the counterbore is machined at the max inclination WRT the hole and the part doesn't work, then the tolerance is incorrect.
5. An alternative is to use the example in FIG 5-38 and tolerance the counterbore tighter than the through hole. Notes are never an option when there is a geometric tolerance available.

Opinions are the reason that standards were created; to remove the error in interpretation. There are a few things that are still not addressed in the ASME standard and are still somewhat open to interpretation, this however is not one of them. The paragraph I mentioned in my first post to this thread is clear in it's meaning.

Paul,
Amen to that.


Powerhound
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[KENAT]

ringman,

A counterbore is essentially just a larger diameter step in a hole.

A couterbore tool or bit is a tool designed to create a stepped hole.

They are different things, I do not believe anyone else on this thread is donfusing the two.

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

 

[ctopher]

A dwg should never indicate how the feature is created. Just call out the hole and the CBORE together with one tolerance. How the machinist gets there is up to him/her.
Unless the CBORE is used differently other than for a screw or bolt.

Chris
SolidWorks 07 4.0/PDMWorks 07
AutoCAD 06
ctopher's home (updated 04-21-07)

 

[ringman]

ctopher,

I agree, but in reviewing my old Machinery's Handbook it appears that counterbore is definitely a process using rather specific tools. Hence the question WHY DO WE SPECIFY THE PROCESS on drawings? Why not just the geometry?

 

[KENAT]

Counterbore can refer both to the feature created and the tool used to create the feature.

http://www.answers.com/topic/counterbore-1?cat=technology

http://dict.die.net/counterbore/

While use of the word may have evolved out of the tool or process used to create the feature, its use to describe the feature is now so widespread and ingrained that it's not really specifying a process.

Ctopher, never say never ASME Y14.5M-1994 1.4e does allow processes to be on the drawing in certain circumstances. However it also makes it clear that it is generally to be avoided.


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