Is it legit to use a basic dimension to specify a gage size/location?
Is it legit to use a basic dimension to specify a gage size/location?
(OP)
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.
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.





RE: Is it legit to use a basic dimension to specify a gage size/location?
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.
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RE: Is it legit to use a basic dimension to specify a gage size/location?
Han primo incensus
RE: Is it legit to use a basic dimension to specify a gage size/location?
RE: Is it legit to use a basic dimension to specify a gage size/location?
Frank
RE: Is it legit to use a basic dimension to specify a gage size/location?
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Is it legit to use a basic dimension to specify a gage size/location?
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