GD & T Flashcards
Gd and t
Means of dimensioning and tolerancing a drawing which considers function of part and how this part functions with related parts
Unilateral tolerances
Starts at nominal and increases or decreases
When to use gd and t
Part features are critical to a function or interchangeability
Functional gaging is desirable
When using datum references
When tolerance is not already implied
When it allows better choice of maching processes to made for production
Datums
Theoretically perfect feature
Cylindrical Line Axis Point Surface
Datums must be
Perpendicular to each other
Primary datum
Selected to provide functional relationships, accessibility and repeatability
Functional relationships
Standard of size is desired in manf of a part
Consideration of how parts are orientated to each other is very important
Accessibility
Does anything get in the way
Repeatability
Measurements when producing many identical parts to meet required specs
Secondary datum
Are produced perpendicular to primary datum so measurements can be referenced from them
Tertiary datum
Always perpendicular to both primary and secondary Datums ensuring fixed position
Type of FORM tolerances
Flatness
Straightness
Circularity
Cylindricality
Type of PROFLIE tolerance
Line profile
Surface profile
Type of ORIENTATION tolerance
Perpendicularity
Angularity
Parallelism
Type of RUNOUT tolerance
Circular runout
Total runout
Type of LOCATION tolerances
Concentricity
Position
Symmetry
Basic dimension
Theoretically exact size, profile, orientation or location of a feature or datum target
It’s untoleranced
Have rectangular around the dimension
Mmc
When part weighs the most
Ensures interchangeability
LMC
When part weighs the least
RFS
Requires condition of material not be considered
Position tolerance
Total permissible variation in location of a feature about its exact true position
Datums are required
Virtual condition
Worst case boundary generated by the collective efforts of size features specified MMC or LMC material
Virtual condition of pin
Gets larger
Take largest size and add geometric tolerance
Virtual condition of hole
Gets smaller
Take smallest tolerance and subtract geometric tolerance
