3 Core Steps for GD&T Step 3) Locate ALL Features with respect to DRF

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Step 1) Establish Datums

i. Identify interface features mating with upper-level items. Regular Coaxial to NO Actual Size NO MMB NO LMB NO MMB & LMB
Datum Axis? Critical?

Locating Features
ii. Determine which d.o.f. can be constrained by potential datum feature(s). FOS Critical? Critical? EQUALLY Critical
a) Usually select datum feature based on max. # d.o.f. it can constrain. YES YES YES YES YES
b) Datum feature must be of adequate size to constrain assigned d.o.f. Size Tolerance Tight Size Tolerance Large Size Tolerance Large Size Tolerance Basic Size
- If datum feature cannot effectively constrain d.o.f., select another feature. & & RFS & 0 M & 0 L &
iii. Are enough d.o.f. constrained to communicate the design intent?
- YES - No further datums required. Go to Step 2. Pattern of Regular Features of Size?
- NO - Select Next Datum Feature (3 datum references MAX) (Step 1.ii)
FOS? YES
Basic Size & Composite Position
Step 2) Control Datum Features NO (NO DRF) & PLTZF - Pattern Locating
Irregular MMB YES
FOS Critical? M With DRF FRTZF - Feature Relating
YES PRIMARY SECONDARY TERTIARY
Size Controls Form OR OR NO
Regular Pattern of Composite Profile of a Surface
FOS? Surface Basic Size Irregular Features of Size PLTZF - Pattern Locating
PRIMARY SECONDARY TERTIARY & or Surfaces?
NO OR OR OR FRTZF - Feature Relating
S

Jim Unrelated Simulator Related Simulators ASME Y14.5 - 2009 GD&T CHEAT SHEET
ASME

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G D

Max
T P

Sykes for verifying feature for simulating datum features ob = SIZE

Senior

± SIZE TOL ± GEO TOL RFS ± GEO TOL BONUS Feature Type d.o.f.
ib NOMINAL
MME L
P.Eng GDTP-S
AME M & RFS/RMB Minimum Material Regular FOS: contains/contained by an actual mating envelope, Complex 6
Actual Mating Envelope Envelope requires directly opposed points & limit on size, establishes center Linear Extr. 5
Cone
A B C
5
0.02
Irregular FOS: contains/contained by an actual mating envelope

FILE
M M L Any Datum Feature Identifier or FCF associated with a Regular FOS Cylinder 4
Plane 3
(or similar) establishes or controls a center -point, -axis, or -plane
Sphere 3

R
TH I W
IS F N PO ITHI
AC OF @
MM
WIT DA
TU
Profile of a Surface: the only geometric control that locates surfaces
YLI 0.0 HR



EA SITI N ND 2 C ES MS d k j t h r i a f b c u g e
TU A, B
RE ON RIC
AL
PE
CT @ § §
IS T
OB
TO
L
TO MM Datum
E
ER
ANC
B, C
@
LM
Referencing                
EZ B
ON
GD&T Hierarchy E
Location                
Location Rule #1: Size controls form for regular FOS
Orientation
(Full Form check @ MMC / Two-Point check @ LMC). Orientation                
Rule #2: RFS is default on geometric tolerances.
Size RMB is default on datum references. Form 
3-D

3-D

2-D

2-D  
3-D

2-D      
3-D

2-D

3-D

2-D
Form Screw Threads: default ØPITCH - specify ØMAJOR / ØMINOR § WITHOUT DATUM REFERENCES, ONLY SIZE & FORM CAN BE CONTROLLED