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?

 

[powerhound]

A counterbore is a process AND a feature, just like a countersink. When the symbol for a counterbore is shown, it is specifying the feature, not the process. The same goes for a countersink. It's not specifying the process or the tool to do it, it just says to apply a countersink to the dimensions specified. As far as using specific tools for the counterbore; as I said before, I never use a counterbore tool yet I still am able to create a counterbore. That's because the tool, the process, and the feature are 3 different things.

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

 

[powerhound]

A+ to KENAT...

Man you really do your homework. I just finished up my post and noticed you had squeaked one in on me.

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

 

[KENAT]

So give me a star;-)

There are a lot of questions discusions I don't/can't contribute to due to lack of experience etc. This topic however, is something I've looked at before and discussed with someone far more knowledable than I, so I'm going to town.

That way when I ask a question hopefully people answer.

I'll scratch your back...

Putting, or even hinting, at processes on a drawing is a red flag for me, I'll usually go off about even a poorly worded note.

However, in this case I don't see putting Counterbore or |_| (that's meant to be the symbol) as implying a process.

On the other hand, someone says "DRILL HOLE .125" or DRILL & TAP 8-32" I'll slap their wrist!

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

 

[WHITMIREGT]

KENAT: I do not disagree with your comments. My thinking was:

1.The text in paragraph 5.7(a) stated “ZONES”, and the text in figure 5-37 states “ZONE”. Which one is correct? I do not know. That is why I said a note under the feature control frame may be needed if there is a chance that the wrong definition may be used.

2.If the two axes tilt in two opposite directions, you are correct the hole sizes need to be calculated.

3.I should not have mention an implied counterbore tool, I know we do not mention the process on a drawing.

Thanks KENAT, I need to be more accurate in my statements.

 

[KENAT]

Gary, you're probably more likely to know than I but given what 1.1.4 says about figures I'd expect the paragraph to take precedence over the figure, although it's not cut & dried.

This is the first time I've seen the confusion amongst what I'd take to be mostly fairly knowledgable parties, so up to now it's not something I'd have thought needed clarification.

This may be something worth pointing out to the ASME commitee for consideration for correction/clarification. I strongly suspect the figure needs correcting but I could well be wrong.

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

 

[ctopher]

Kenat,
I'll give you a star. Well said.

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

 

[ringman]

One might consider that the hole for the body of the screw would require a closer positional tolerance than the one for the clearance of the screw head. Comments?

Then the question, what controls the relationship for the seating surface for the screw, if not the process?

Comments?

 

[ctopher]

Positional tolerances do. Various processes can get you there one way or another.


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

 

[CheckerRon]

I concur with Gary and Kenat on the "jist" of the callout. If you are using the symbol for CBORE and not the word (and you should be), then it ought to bre clear that you are delineating a feature shape, and not a machining process. Regarding ringman's last comment, I call out One FCF, and one tolerance for both the hole and its associated cbore, but I set the size of the cbore such that the screw shank limits travel at worst case tolerances rather than the screw head touching the cbore dia first. To do this, one may have to make the cbore larger than many of the screw charts out there. Moreover, I will use a looser tolerance (say +/-.005" on bolts <1/2" dia) on the cbore and stick with normal and close tolerances on the bolt shank and bolt hole. This may preclude using commercial counterboring tools in many cases, but many CNC machines are using end mills anyway. Machine tool makers have some pretty tight size tolerances on the cbore dia of many of the the counterboring tools relative to screw sizes, and I don't see many designers taking that into consideration with the hole position tolerances they specify.

 

[KENAT]

ringman,

Your first point is covered in 5.7 b & c. However my preference is to have a single FCF and just make sure the Cbore dia is big enough to accomodate tolerances from all other features/components (as CheckerRon). As I mentioned earlier and CheckerRon says, this can end up ruling out a lot of 'off the shelf' counterbore bits. The use of a larger C'bore with looser tolerance achieves almost the same thing as a looser positional tol due to 'bonus tolerance'.

"Then the question, what controls the relationship for the seating surface for the screw, if not the process?
"

Umm, am I missing someting here? The tolerances on the drawing control the relationship.

The combination of the positional tolerance, the diameter tolerance and the c'bore depth tolerance should take care of this. If you aren't specifying all these then your drawing is incomplete. There are at least 2 common processes for creating a counterbored hole, either using a c'bore bit or creating the hole and c'bore separately as a 2 stage process. If the drawing is created properly and the processes done correctly both are perfectly good options.

Ron,

I don't think Gary & I quite agree. We both agree that figure 5-37 doesn't quite match the wording of 5.7a. The paragraph clearly says zones, the figure says zone. I believe that the paragraph takes precedence over the figure and so there isn't any ambiguity, the figure is just slightly wrong. Gary doesn't agree that the paragraph necessarily takes precedence and so believes it's ambiguous and should be clarified with a drawing note or similar.

What do you think?

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

 

[ewh]

I don't see the ambiguity, as the figure shows two zones, even if it uses the word "zone", as it is an example of separately controlled hole/counterbore. But then again, I didn't dig too deeply, as I have enough to ponder checking some GD&T that the designer obviously didn't understand.

KENAT, how would you like some side work?

 

[KENAT]

ewh, I'm pretty sure your understanding would be better than mine, although checking GD&T that the Designer didn't understand is becoming my specialty.

I have side work, it's called trying to check for the other half of the business as well as the half CheckerRon used to take care of;-)

CheckerRon might be interested though if it's any more than a joke.

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

 

[ringman]

Ctopher,

My question with regards to the seating of the screw head on the CBORED hole, is based on the example in the standard. The only control that is apparently indicated is the one which controls the depth. The depth allowance quite probably could exceed the angular misalignment with the body of the screw. Where is the refinement, if not controlled by the tool? Perhaps the example in the Standard needs some refinement.

Lets not forget that the Standard is supposed to provide for a "universal' interpretation of drawings.

Another look at the example, and I ask "What is gained by the inclusion of the symbol for CBORE?. Would it not fly just as well without it?" There is a diameter and a depth.

 

[KENAT]

ringman.

If the depth of the cbore has a fairly large tolerance then yes, the bottom of the cbore could be at quite an angle.

If this is problem you need to add a tolerance (eg, perpendicularity to the bore or more likely parallellism to the surface) to correct it.

The tool/process controls nothing, it is used to meet the requirements on the drawing. If you have a requirement it needs to go on the drawing.

Read paragraph 1.1.41 closely before you start talking about the figure being incomplete etc.

As to the symbol, are you serious? It's a clarification. If you have a cross section as figure 5-37 has then yeah it's pretty clear which diameter and depth is which. Without the cross section it may not be clear.

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

 

[ewh]

To expound on KENATS last post, if the hole is not shown in a cross section, then ommitting the cbore symbol would necessitate noting the bottom profile (flat bottom) or risk getting a drill point angle.

 

[WHITMIREGT]

I do agree that the text is primary. On August 7th I did a white paper on counterbores showing two separate tolerance zones for a drawing having one positional control. When I was working on the DRM, I saw the word “ZONE” in Figure 5-37, so I asked the question on ENG-TIPS as to what members thought. I will stick with the two separate zones as stated in the Y14.5 text and my white paper. So before I dig myself another hole, I would like to thank everyone for their input.

 

[ringman]

Again, taking the example at face value for the depiction provided, what is the benefit if any of having the symbol added? Is there any? Gary?

 

[ctopher]

I have seen dia and depth called out without the CBORE symbol. The outcome was a drill point where the CBORE should be. It's a good indication of what the feature should look like. The symbol should also be known with different languages.

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

 

[ringman]

EWH,

What if the depth tolerance were sufficient to allow a csk to be acceptable? Again, it seems that the CBORE tool controls the angle of the seat and additionally the corner radius. Radius not previously mentioned in this thread, if I am not nistaken

 

[powerhound]

On page 1 of the standard, paragraph 1.1.4 it states that sometimes figures are incomplete by intent. This is probably one of those cases where the idea of how to tolerance a counterbore using a single FCF and how to interpret it was all that the figure was intending to show.
Even taking that into consideration, I'm not sure what the dilemma is regarding the seating of the screw head. The axis of the hole will govern the orientation of the bottom of it and the axis is controlled by the tolerance in the FCF. I don't really know why you are so hell bent on eliminating the CBORE symbol from the standard. I suppose you think CSINK should go with it.
I make the above comment in a quasi-jovial manner. I don't intend disrespect, I'm just a little amazed at how this point is being belabored...and I'm guilty of perpetuating it.
Anyway, I won't belabor it any more.

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