Working with Contact Path Properties

Probe Toolbox - Contact Path Properties tab

The Contact Path Properties tab becomes visible when you have the Auto Feature dialog box open (Insert | Feature | Auto) and a contact probe is enabled. This tab contains several items that you can use to change various hit properties for auto features that use contact probes.

A useful way of visualizing how these properties affect the measurement is to display pathways and hits by using the Show Hit Targets icon .

Depending on the type of feature that you select in the Auto Feature dialog box, this tab may change to contain one or more of these items:

Hits

This item supports the Line, Circle, Ellipse, and Round Slot auto features. It defines the number of hits that PC-DMIS uses to measure the feature. The number of hits you specify are equally spaced between the start and end angles.

Location of hits

(A) - Start angle

(B) - 3 Hits

(C) - 4 Hits

(D) - 5 Hits

If you don't type a length value (or the value is zero), PC-DMIS uses the current probe tip's diameter as the distance between points.

Depth

This item supports the Edge Point, Line, Circle, Ellipse, Round Slot, Square Slot, Notch Slot, and Polygon auto features. It defines where PC-DMIS takes hits on the feature itself and its surrounding sample hits.

Auto Feature

Description

Edge Point, Notch Slot

If you enter one, two, or three sample hits, then PC-DMIS applies the depth value from the measured surface value.

Depth for Edge Point

A - Target hit
B - Sample hit
C - Depth

Circle, Ellipse, Round Slot, Square Slot, Polygon

For these features, PC-DMIS usually applies the depth value as a positive offset distance along the IJK centerline vector. The vector originates at each feature's center point. While the software allows negative depth values, this is not recommended for contact-based measurements of these features. For example, consider these two cases:

  • Case 1: If the nominal center point is at the base of the external feature, the depth would be the distance from the bottom of the feature.

  • Case 2: If the nominal center point is at the top of the external feature, the depth would be the distance from the top of the feature.

A negative value in the first case would cause the probe to move into the surface material surrounding the feature, possibly causing a collision.

A negative value in the second case would be desired for the probe to properly contact the feature, whereas a positive depth value would move the probe above the feature where no material would exist for the probe to contact.

Important Considerations:

Centerline vector (IJK): The vector of the feature should point away from the plane in which the feature lies (2D feature). If sample hits are involved (for 2D or 3D features), that vector should reflect the approach vector for those sample hits.

Height or Length: If the feature has a length or height with a negative value, PC-DMIS flips the vector orientation.

The orientation of the vector along which the positive depth is applied (IJK') changes based on these conditions:

External features:

IJK' = IJK in case the feature has a Height or Length greater than or equal to zero.

IJK' = -IJK in case the feature has a Height or Length less than zero.

Internal features:

The IJK' for internal features points in a direction opposite that of external features.

Line

The software applies the distance as a positive value along the perpendicular vector to the line vector and edge vector.

The line's depth depends on the direction of the hits in relation to the current coordinate system. For example, if you have a typical orientation (X/Right, Y/Back, and Z/Up), and you take your first and second hits from left to right on the model, then you need to use a positive depth value. However, if you take your first and second hits from right to left on the model, then you need to use a negative depth value.

Starting Depth

This item supports the Cylinder and Cone auto features.

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Ending Depth

This item supports the Cylinder and Cone auto features.

Ending offset

This item supports the Cylinder and Cone auto features.

Hits (Total)

This item supports the Sphere auto feature.

Hits Per Level

This item supports the Cylinder and Cone auto features.

At least six hits and two levels are necessary to measure a cylinder or cone (three hits at each level).

Hits Per Row or Hits per Ring

This item supports the Plane auto feature.

Hits Per Side

This item supports the Polygon auto feature. It defines the number of hits taken per side on a Polygon feature.

Levels

This item supports the Cylinder, Cone, and Sphere auto features. It defines the number of levels the software uses to measure the feature. You can use any integer greater than one. The software places the first level of hits at the Starting Depth and the last level of hits at the Ending Depth.

Pitch

This item supports the Circle and Cylinder auto features. For threaded holes and studs, the Pitch value (also known as "threads per inch") defines the distance between threads along the axis of the feature. This allows for more accurate measurements of threaded holes and studs. If the value is anything other than zero, PC-DMIS staggers the feature's hits along the feature's theoretical axis, spacing them around the feature using the Start Angle and End Angle values in the Auto Feature dialog box.

For details on pitch values for various thread sizes, please consult an appropriate authority (such as the ASME standard).

Example: If measuring a circle with four hits equally spaced around the circle:

Rows

This item supports the Plane and Sphere auto features. It defines the number of rows that the software uses to measure the feature.