DCF (Dual Cylinder Fit) is the major enhancement for VTube-LASER in version 2.8 (April 19, 2017) because it replicates measuring the tube TWICE in one pass when the user measures the tube the first time.

This ensures repeatability of the cylinder measurements on-the-fly using a LASER scanner.

When using the LASER scanner*, the DCF feature divides the cylinder surface data into two groups, then calculates the cylinder data and intersection points twice to verify repeatability.

As of VTube-LASER v2.8.1, it works in both UNISCAN and MULTISCAN modes.

*(Note: DCF is not used tactile measurements because it is assumed that there isn't enough data to perform DCF properly with ball probe measurements.)

The DCF Point Repeatability value is reported in the Cylinder Fit window (see CHECK 4 below).

What happens if the points are too far apart?

If the two DCF points are too far apart (the Point Repeatability value is too high), then VTube-LASER will warn you and ask for a remeasure. This allows you to remeasure the straight to guarantee that the measure repeats before moving to the next straight.

What happens if the points are close to each other?

If the two DCF points are near to each other within tolerance, then VTube uses the average of those two points as the final point. See the illustration on the right.

See the five-minute video of the feature explained by Michael Cone - the developer of VTube-LASER.

• View on Vimeo
• View MP4

As part of the DCF feature, the Cylinder Fit Data window reports cylinder fit values that help you know if the cylinder measurement is good.

When using the laser scanner in Uniscan mode, VTube cylinders must pass a total of FIVE checks to be qualified as good cylinder scans.

(Versions before 2.8 only required CHECK 1 shown below. This 5-level check is only available in version 2.8 and newer.)

CHECK 1 - MAXIMUM WOBBLE PREDICTION

The Maximum Wobble value predicts how precise the surface data fits the cylinder. This was in previous versions, but now two cylinders must pass - not just one. And we've created a single new value to display at the top rather than multiple XY values.

CHECKS 2 and 3 - CYLINDRICITY and OOR%

The new CYLINDRICITY value reports the difference between the lowest and highest points on the measured diameter relative to the centerline. If the values get too far from each other, then VTube-LASER will warn you.

Also, the OOR% (Out-of-round%) is reported and used to qualify the cylinder fit. This is active for both LASER and ball probe.

CHECK 4 - NEAREST PASS DISTANCE

The Intersection Pass Distance shows how near each intersecting 3D centerline comes to each other in 3D space. If the Nearest Pass value is more than the Nearest Pass Tolerance, then VTube-LASER will warn you. This is active for both LASER scanner and ball probe. See VTube-LASER Nearest Pass for an illustration.

CHECK 5 - DUAL CYLINDER FIT

As mentioned above, because the DCF engine creates two cylinders, it always builds and compares the resulting intersection points from both cylinders. It warns you if they don't match well enough.

The Cylinder Fit Data window is color-coded to help you quickly determine where the problem lies in the data.

RED PANEL

This would indicate a major problem in the cylinder fit calculation. VTube requires a remeasure of a straight section.

GREEN PANEL

All green indicates that no issues were found in all four checks. You can trust the calculation.

Intersection Pass Distance Warning Test

This is an example of the Intersection Pass Distance warning test.