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?

 

[KENAT]

ringman, have you read paragraph 1.1.4 regarding figures?

1.1.4 Figures. The figures in this Standard are intended only as illustrations to aid the user in understanding the principles and methods of dimensioning and tolerancing described in the text. The absence of a figure illustrating the desired application is neither reason to assume inapplicability, nor basis for drawing rejection. In some instances, figures show added detail for emphasis. In other instances, figures are incomplete by intent. Numerical values of dimensions and tolerances are illustrative only.

You can't really take the figures at face value for anything more than the specific point they're trying to illustrate, and even then in this case there is the zone/zones ambiguity.

ewh (and ctopher) explanation for the cbore symbol is even better than mine.

If you must insist on taking 5.37 literally then... There is no indication of where the cross section is taken/where it shows. i.e. There is no section line "A-A" and the section itself doesn't say "Section A-A" so there, the Cbore symbol is needed so we know it's a Cbore and not a CSK or even a male feature.

Gary, sorry my misunderstanding of your viewpoint.

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

 

[KENAT]

For ***** sake. The tool or process CONTROLS nothing.

The angle has to be in the limits of the depth tolerance. For extreme angles then the orientation of bore will control how the screw sits as Powerhound points out.

The corner is sharp within any relevant tolerances or drawing notes about sharp edges etc.

There's no guarantee a cbore bit will be used to create the cbore hole, it's just as likely these days to be a 2 stage operation with an endmill for the cbore.

Sorry, got a bit carried away there. Powerhound probably has a point, the smell or rotting equine flesh will soon fill the air, que ewh with his favourite emoticon.

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

 

[ctopher]

I agree. Calling out a CBORE has nothing to do with the process. It can be dug out by a toothpick, as long as it meets the drawing.

http://www.draftingzone.com/shoppingzone/6-1.pdf

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

 

[WHITMIREGT]

ringman
The symbol is redundant.

Gary

 

[ewh]

ringman,
If the depth tolerance were sufficient to allow a csk or a drill pt to be acceptable you would be better off specifying a counterdrill, for which you don't need a symbol.

 

[ringman]

Gary,

Thanks.

I did a quick check on CAD of the example in the Standard and the tolerances on the example allow an angle on the seat of approx 15 degrees off horiz. (Worst case).

 

[powerhound]

I only came up with 4.29 degrees off horizontal. I think your "quick check" was a little too quick.

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

 

[ringman]

Powerhound,

I did a recheck and with a triangle of 1.554, .4, and 1.5,based on the diameters and depth, I still come up with 15 degrees. What are your figures to arrive at 4.29 degrees?

I used diameters of 6.4 and 9.4 and a depth of .4.

 

[KENAT]

Diameter 9.4, depth tol range of .4, I cheated and drew the triangle in CAD, it says it's only 2.44 off horizontal?

This assumes constant angle across the dia of the C'bore etc.

What am I doing wrong?

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

 

[ringman]

Well, Not for sure, but the triangle I drew represents the width of the seat for the head, based on the smallest head clearance hole and the largest body clelarance hole. .4 is the depth.

This is only one side of the seat in the section view.

Does that make sense?.

 

[KENAT]

Yep, if you're looking at only the land, and acting as if it had been made as a shallow csk then 15 degrees is about it.

Included angle of the csk about 150 degrees.

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

 

[powerhound]

ringman,
I only checked the deviation of the c'bore because as I said before, it is a separate feature. I drew the counterbore at LMC to get the largest amount of deviation so the diameter is 9.6, which makes the tolerance zone .45 in diameter. If you draw a line from X-.225 Y0 up to X.225 Y6.0 (6.0 represents the depth of the c'bore) you will get an angle from 0 of 4.59 degrees. If you make the counterbore to it's MAX depth of 6mm, the angle is 4.29 degrees.
For the purposes of furthering the cause. I checked the entire depth of the counterbore and hole as if it were one feature and came up with the same thing as KENAT.

What are we missing?


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

 

[ringman]

Powerhound,

If I read this right, you are looking at the angle of the axis of the dia as allowed by the pos tolerancing. (I believe then your angle would be off the vertical) I am looking at the seating surface for the head, and looking at the worst case with dimensions provided. We are apparently looking at 2 diff things entirely.

My look at the worst case was assuming that we use this 'special toothpick' to generate the hole to the dimensions. This rather than a counterbore tool.

 

[KENAT]

ringman, there's no implication that a c'bore tool has to be used to make the c'bore. It is very likely the c'bore feature is made using an end mill or something, what's so confusing about this? The feature on the part as defined by the drawing is process independant.

I'm also not convinced the included angle of 150 degrees is truely worst case. In this case the edges of the screw head will still sit on a fairly even contact it will just be a very narrow ring, under a lot of load they'll probably brunel the cbore a bit. For many applications this probably wouldn't cause too much problem. In some it may in which case an extra/tighter tolerance should be called out on the drawing.

I'm pretty sure I've lost interest now.


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