Add datums and feature control frames

Geometric tolerances (GD&T) say how flat, square, round or well placed a feature must be. Mark the faces the part is measured from with datum feature symbols, then add a feature control frame to each feature you tolerance. Moket draws both to ISO 1101 or ASME Y14.5, the sheet's standard, and checks each frame against the standard's rules.

Access: Datum and GD&T on the drawing toolbar.

Add a datum

1. Click Datum.
2. Click the edge of the face that is the datum, in a view that shows the face edge on. To make a feature of size (a bore, a pin) the datum, click its dimension instead.
3. Click where the letter goes.

The datum takes the first letter no other datum or view of the drawing uses; change it under Letter. Each letter is used once on a drawing.

Add a feature control frame

1. Click GD&T.
2. Click the edge of the toleranced face. To tolerance a feature of size, such as a hole's position, click its dimension: the frame then tolerances the feature's axis or center plane.
3. Click where the frame goes: the point is its lower left corner, and a leader runs to the feature from the side of the frame nearest it.
4. In the frame's properties, set:

Option	What it does
Characteristic	Straightness, flatness, circularity, cylindricity, profile of a line or surface, parallelism, perpendicularity, angularity, position, concentricity, symmetry, circular or total runout
Ø	A cylindrical tolerance zone, as for the position of a hole
Value	The width of the tolerance zone, in the drawing's units
M L P F T U CZ	Modifiers: maximum or least material condition, projected zone, free state, tangent plane, unequal profile, combined zone
Datums	Up to three letters in order of precedence, separated by commas. A letter followed by M or L takes that material condition: A, B M. A common datum made of two features is written A-B

A frame on a dimension made with GD&T starts as a position tolerance with a cylindrical zone, referring to the datums already on the drawing. A frame on an edge starts as flatness.

The rules Moket checks

Moket flags a frame that breaks a rule of the standard; the problem shows in the frame's properties and in the Problems list:

Message	What to do
Flatness is a form tolerance and takes no datum	Straightness, flatness, circularity and cylindricity refer to no datum: clear Datums
Parallelism needs a datum	Orientation, location and runout tolerances refer to a datum: add one
Flatness has no cylindrical zone: take Ø off	Only straightness of an axis, position and concentricity take a cylindrical zone
M applies to a feature of size: put the frame on its dimension	Material conditions apply to holes, pins and slots: add the frame on the feature's dimension
Datum B is not on the drawing: add its datum feature symbol	ASME drawings: every datum a frame names must be marked with Datum
Datum A is used twice: give each datum its own letter	Change one of the letters

A datum or frame whose edge is gone from the part shows as lost, like a dimension.

Related

• Surface texture
• Tolerances and fits
• Dimension a drawing