12.3 Distance, Angle & Tangent Mates

12.3 Distance, Angle & Tangent Mates

Quick Answer: Use a Distance mate for a controlled gap/offset, an Angle mate for a controlled orientation in degrees, and a Tangent mate when a cylinder/sphere must touch a face or curve without sharing an axis. On modification questions, edit the mate dimension (for example 10 mm → 15 mm), rebuild, and re-run Mass Properties.

Coincident and Concentric place most parts. Distance, Angle, and Tangent handle clearances, angled poses, and curved contact—and they are especially important when CSWA assembly items ask you to change a key parameter and report a new mass or center of mass. These three mates are part of the official standard set alongside the four from 12.2.

Distance mate

Distance maintains a specified separation between selected entities (commonly face–face or plane–plane).

When the drawing wants Distance

• A plate floats 5 mm above a base (not flush)
• Two parallel faces must keep a slot width style offset realized by part faces
• A stop face sits a documented air gap from another face
• The problem later says: “Change the distance mate from 8 mm to 12 mm”

Distance workflow

1. Mate → select two faces (or valid pair).
2. Choose Distance.
3. Type the value in document units (MMGS → millimeters).
4. Use direction/flip controls so the gap is on the correct side.
5. OK → drag-test (motion should respect the locked gap).

Distance vs Coincident

Modification pattern (high value on exam)

CSWA loves multi-step assemblies:

1. Build mates including Distance = d₁.
2. Measure assembly mass / CoM → enter answer A.
3. Edit Distance to d₂ (double-click mate dimension or Edit Feature on the mate).
4. Rebuild → Mass Properties again → answer B.

Do not delete the mate and rebuild the whole stack if you only need a value change. Editing preserves the rest of the constraint network.

Distance traps

Angle mate

Angle locks the angle between two entities (faces, edges, planes) to a typed degree value.

Exam uses

• Bracket folded at 30° to the base
• Lever arm orientation 45° from a reference face
• Modification: change angle 20° → 35° and re-measure CoM (angles move mass in space without changing part volumes—mass may stay the same while CoM coordinates change)

Angle workflow

1. Select two faces/edges that define the angle on the drawing.
2. Mate type Angle → enter degrees.
3. Flip/alignment options orient which quadrant the angle opens into—critical.
4. Preview against the isometric; OK; drag-test.

Angle vs Perpendicular vs Parallel

Mass vs CoM after angle edits

Changing only an Angle mate reorients parts. Total mass is usually unchanged (same parts, same materials). Center of mass coordinates almost always change. If the exam asks for mass after an angle-only edit and your mass moved, you accidentally edited geometry or material—not only the angle. If it asks for CoM and yours did not move, the angle mate may not have been the driving orientation (another mate still locked pose).

Tangent mate

Tangent forces tangency between selected geometry—classically a cylinder or sphere against a planar face, or curve-to-curve tangency where supported.

Exam uses

• Roller or pin resting against a flat pad (not concentric to a hole)
• Sphere sitting on a plane
• Cylindrical cam/follower style contact simplified for associate-level geometry
• Situations where Coincident face–face is impossible because one “face” is curved

Tangent vs Concentric

Putting Concentric on a cylinder and a plane fails; putting Tangent on two hole axes is the wrong mental model—use the mate that matches contact type.

Tangent workflow tips

1. Select cylindrical face + planar face (common case).
2. Mate → Tangent.
3. Flip if the cylinder goes to the wrong side of the plane.
4. Combine with other mates (coincident on end faces, parallel on a flat) to remove remaining DOF.

Combining mates: realistic stacks

Example A — Offset cover

1. Concentric: cover bosses ↔ base holes (or multiple concentric as needed).
2. Distance: underside of cover ↔ base top = 2 mm standoff.
3. Parallel or a third constraint if rotation about vertical remains and must be fixed.

Example B — Angled bracket

1. Coincident: bracket back ↔ vertical wall (or edge hinge setup per drawing).
2. Angle: bracket face ↔ base top = 60°.
3. Optional coincident of a side face to a mid plane for left/right position.

Example C — Cylinder against stop

1. Concentric: rod in sleeve (slides).
2. Tangent or Distance: rod end condition against a face per drawing.
3. Drag along axis if still free—add mate if design should be fixed for mass answer.

Modification questions: edit, don’t rebuild

Read the stem: mate parameter vs part feature parameter. They are different edit paths. Mate edits stay in the assembly FeatureManager under Mates. Part edits require editing the component.

Note on mass with Distance: If Distance only separates rigid bodies further in empty space without changing part solids, total mass is unchanged; CoM can still shift. If the exam reports mass changing after a “distance” step, look for a part dimension change, configuration, or suppressed body—not only a pure gap mate.

Alignment and preview discipline

Numeric mates are easy to accept with a wrong flip:

• Distance 10 mm the wrong direction can push a part into the base (interference) or away opposite the isometric.
• Angle 30° the wrong way mirrors the mechanism.
• Tangent the wrong side parks the cylinder through the solid.

Always:

1. Watch preview before OK.
2. Compare to exam isometric.
3. Run Interference Detection if something looks buried (Chapter 13 deepens this).
4. Drag-test remaining freedom.

Exam time box for numeric mates

Within a ~18–20 minute assembly budget:

If a Distance mate fights an existing Coincident on related faces, stop stacking—diagnose conflict (12.4) rather than adding a fifth mate “to push harder.”

Practice drills that transfer to CSWA

1. Shaft-in-plate with shoulder coincident; add a Distance standoff version; edit 5→10 mm; record CoM each time.
2. Hinge-like bracket with Angle 0°, 45°, 90°; confirm mass constant and CoM moving.
3. Cylinder Tangent to a plane plus end coincident; flip tangent side once on purpose and see the failure mode.

Distance, Angle, and Tangent turn assemblies from “touching parts” into parameterized mechanisms the exam can score twice—once at the initial pose and once after a key edit. Pair them with DOF awareness (12.4) so underdefined free motion does not silently corrupt your second measurement.