On Wednesday, January 29, 1997 at 2:00:00 AM UTC-6, Marty Wright wrote:

ASME Y14.5M-1994 uses the same drawing symbol to delineate both a
spotface an counterbore and defines each of the terms as follows:

1.8.11 Counterbored Holes. Counterbored holes may be specified as
shown in Fig. 1-36. Where the thickness of the remaining material has significance, this thickness (rather than the depth) is dimensioned.
For holes having more than one counterbore, see Fig. 1-37.

1.8.13 Spotfaces. The diameter of the spotfaced area is specified.
Either the depth or the remaining thickness of material may be
specified. See Fig. 1-40. A spotface may be specified by note only and
need not be delineated on the drawing. If no depth or remaining
thickness of material is specified, the spotface is the minimum depth necessary to clean up the surface to the specified diameter.

The use of the same drawing symbol for both terms with differing
definitions prompts several questions:

1. Is there a functional difference between a spotface and a
counterbore?

2. If so, what is the difference? Are they measured differently?

3. If there is a functional difference, how can one tell a spotface
from a counterbore when the same symbol is used for each?

4. If there is no functional difference, then why do we need two
different terms?

5. Where no depth or remaining thickness of material is specified for a spotface, does the actual local size control how deep the spotface is
allowed to go? Can it get thinner than the specified size in the
spotface area?

6. How can a toleranced diameter for a spotface be verified when a full diameter may not even be apparent on the produced part? (It’s common to see spotfaces which produce a "crescent" shape on the surface in
achieving surface cleanup) For this reason, should spotface diameters
always be expressed as a minimum surface area rather than a toleranced dimension?

I would like to hear others thoughts with regard regarding spotfaces and counterbores. Please post responses to the NG.

Thanks in advance!
-- ***************************************************************************** Marty Wright
Lockheed Martin - Tactical Aircraft Systems
PO Box 748 Mail Zone 2283
Fort Worth, Texas 76101 ***************************************************************************** Email: mpwright@lmtas.lmco.com
Phone: (817) 763-1656 Fax: (817) 763-1111
LMTAS Dimensional Management: http://webster.lmtas.lmco.com *****************************************************************************

I WAS 8 YEARS OLD WHEN YOU POSTED THIS, AND I HOPE THAT SOMEHOW THIS GETS BACK TO YOU THOUGH I AM SURE YOU'VE FIGURED IT OUT BY NOW!. THE DIFFERENCE BEING THAT A COUNTERBORE IS SPECIFICALLY TO ALLOW FOR OTHER PORTIONS OF THE COMPONENT TO RECESS BELOW THE
FACE OF THE COUNTERBORED PIECE. A SPOT FACE IS SPECIFIED WHEN THE SURFACE NEEDS TO HAVE A FLAT, BE IT ON A CASTING OR FORGING OR CONTOURED SURFACE, SUCH AS WHEN SEALING A FLUID PORT AGAINST A FLAT SURFACE

-DUSTIN

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