Is it legit to use a basic dimension to specify a gage size/location? 1

[Medmaker]

In my past I've seen and used the basic dimension callout to specify a gage location or the size of a gage ball or pin on a drawing. I've seen a couple of threads here that describe it as well. I'm curious if the standard supports this at all and if so where, or are there alternative methods.

I've attached a drawing showing two separate examples. The first being a conical taper that is being inspected by air gage. The "basic" locations given are the locations of the air ports. The gage works by determining the two diameters and then reports one diameter and the taper angle as calculated. There are certainly better options for using proper GD&T to specify a taper, but in terms of how the part is inspected and what is being inspected, it appears correct.

The second example is a dovetail. The "basic" dimensions represent gage pins. There is obviously room here to use something like surface profile to better specify the surfaces, but again, this is a common inspection method. A similar example would be inspecting a tapered bore with gage balls and using a drop indicator.

If we assume standard gage tolerances apply (or at least specified elsewhere) are these uses acceptable? Everything I've read seems to indicate that you need a feature control frame somewhere if you are using a basic dimension.

Thanks for your comments.

 

[dgallup]

ISO 3040 shows the use of basic dimensions to specify tapers although it says both the length and diameter should be basic and to use a profile control to give the tolerance.

I've seen basic gage pin dimensions used like your second example and I have used gage balls with basic dimensions but I don't know where it's in the ISO standards.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[DanStro]

The way I understand from ANSI a basic dimension says "this is controlled by GD&T that is also found on this drawing". But what you are describing sounds like they should be reference dimensions because they are not controlled on the drawing that they are shown on. At least in the case of the gage ball illustration?

Han primo incensus

 

[Medmaker]

Thank you for the replies thus far. DanStro, I agree that reference dimensions might be an alternative. I think that the basic dimension symbology was used to express the theoretically perfect nature of the measurement or gage ball/pin. Reference dimensions to me always seems to infer that that dimension is a resultant of the driving dimensions. In these cases, the basic dimensions are driving dimensions. In the past I've also place the words "Gage Ball" or just "Gage" under the dimensions in question.

 

[fsincox]

I agree with Medmaker, I have see basic angles called out with toleranced location before, too, they are just trying to control some of the variability of the implied tolerances.
Frank

 

[MechNorth]

When gage sizes/locations are specified as BASIC, they are controlled by gagemaker tolerances. (ASME Y14.5)

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[ewh]

I agree with Jim, but have not had the standards nearby to verify.

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV