When selecting a gage for your inspection needs, picking the correct tolerance for your gage is imperative to manufacturing quality into your workpiece. Let MWS, and Vermont Gage (www.vermontgage.com) help you select the proper gaging for your application.
GAGE TOLERANCE SELECTION THE 10% RULE: PLUG GAGES
10% Rule
The 10% Rule is intended to assist in the selection of the tolerance for Go & No-Go gages. The premise is; if you surrender 10% of the total product tolerance to the gages, you will pass 90% of your product tolerance 100% of the time, if the Go fits and the No-Go does not.
Go Plug Gage
Using the minimum diameter of the hole as the Go and applying the tolerance PLUS insures that, if the Go plug goes through the hole, the hole is larger than the the minimum diameter. if the tolerance is applied minus on the Go , it is possible to accept product below the minimum stated diameter.
No-Go plug Gage
Using the maximum diameter of the hole as the No-Go and applying the tolerance MINUS insures that, if the No-Go plug does not enter the hole, the hole diameter is smaller than the maximum diameter of the hole and in tolerance. If the tolerance is applied plus on the No-Go plug, it is possible to accept product above the maximum diameter of the hole.
See ASME B89.7.3.1 for more information on the 10% Rule and options beyond this rule.
CALCULATING GAGE TOLERANCES PER THE 10% RULE IS GRAPHICALLY EXPLAINED ABOVE. THE MATH IS SHOWN BELOW:
Hole Size =.250 +.004"
Product Tolerance = .004"
.004 x 10% = .0004"
.0004 X .5 = .0002"
.0002" = Class ZZ Tolerance per ASME B89.1.5 (See Tolerance Chart Below)
GO Plug Gage = .250 +.0002" (Suggested)
NO-GO Plug Gage = .254 -.0002" (Suggested)
