### Creating "Two-Point" Measured Slot Features

Similar to creating "Single-Point" measured circle features, portable devices can also create a measured square or round slot feature by taking only two hits, one on each end of the slot. This is termed a "two-point" slot. This is useful when attempting to measure a slot with a probe whose sphere size is larger than the slot's diameter and therefore cannot fit entirely into the slot to take the usual minimum number of hits required for a measured slot. In this case, PC-DMIS creates the feature at the intersection of the workplane (or projection plane if a measured plane is currently active) and the probe sphere.

Note: See When a Measured Plane Feature Is Not Available for more information.

To create a two-point measured slot feature:

1. Select View | Other Windows | Quick Start to access the Quick Start interface.

2. From the Measure toolbar, select either the Measure Two Point Round Slot toolbar item or the Measure Two Point Square Slot toolbar item.

Note: You don't have to use the Quick Start interface. If desired, you can instead simply click the desired slot feature from the standard Measured Features toolbar. However, this topic assumes that you are using the Quick Start interface.

3. Position the probe as far as it will go down into one of the ends of the slot, and take a hit. The hit should be on the bottom hemisphere of the probe sphere.

4. Position the probe as far as it will go down into the other end of the slot, and take a hit. The hit should be on the bottom hemisphere of the probe sphere.

   - If the probe sphere properly intersected with the workplane (or projection plane) with both hits then PC-DMIS will enable the Finish button.

   - If the first hit did not intersect properly with the workplane or projection plane, a message box will appear that says, "Hit 1 out of range". If the first hit did intersect with the work or reference plane, but the second did not, it will display, "Hit 2 out of range". If you receive one of these error messages, you will need to retake both hits, adjusting your workplane or projection plane as needed so that a proper intersection with the probe sphere takes place.

5. Click Finish. PC-DMIS creates the feature at the intersection of the workplane (or projection plane if a measured plane is currently active) and the probe sphere (see "How It Works" below).

   - The width of the slot is based on the amount of probe sphere that intersects with the work or projection plane when the probe comes in contact with the feature on the part.

   - The length of the slot is based on the distance between the two slot points.

Important: Remember that the calculation is done at the intersection of the probe sphere with the workplane or projection plane. If the probe sphere is too high (it doesn't intersect with the plane at all) or is too low (the hit is on the upper hemisphere or higher), PC-DMIS will generate an error message indicating that the feature has failed.

How It Works:

Side view of the workplane and the probe sphere

A - Probe sphere

B - workplane

h - height of the sphere center to the workplane

R - radius of the measured slot. The slot's width is twice this value.

r - radius of the probe sphere

R = sqrt(r^2 - h^2)

Note: If the probe sphere is so high that r is less than h, the intersection math will fail and PC-DMIS will not solve the slot. If the sphere center is below the workplane (B), PC-DMIS will also not solve the slot.

Notes for Documentation: Two point slot is similar. Idea behind it is that you have a probe that will not fit in the slot and so you put it as far as it will go down in either corner and take a hit on each end. When you do that it computes the width of the slot based on how far down the ball goes and how big the ball is.

This is based on the alignment and the workplane or reference plane. You have to tough it so that the probe intersects that plane. If the ball is too high and the plane doesn't cut through the ball, either the work or the ref plane, then you'll get an error. And it should also give you and error if you go too low, if the center of the ball goes too low.

If you think about the center of the ball. The center has to be within a probe radius of the workplane or the reference plane.

I have made a change so that if the probe is below the plane too far (an infeasible region) then it doesn't solve. The uploaded file is:

V44B\CONSFEAT\BEST_SLOT.CPP

If a workplane is specified then the reference plane becomes the workplane, and the ball center should be above reference plane, but no more than a probe radius. This is also true if a reference plane is selected from the toolbar.

I've been testing and finding minor issues with guess mode in general. There are at least these problem, which I've worked out locally, but want to review with Troy before uploading:

1. When you select a feature type (instead of guessing), then when you take hits it will still potentially guess other feature types until you hit end. These other feature types are shown in the graphics window.

2. If you take more hits than required for a 2 point slot or 1 point circle (I think) then PC-DMIS will add those points. This does not happen for the measured point. You aren't allowed to take more than one hit if you select the point feature type.

Currently I'm in a state where these are fixed, but you are also allowed to make features with too few hits, such as a cylinder with only one hit. I don't think this is all that bad, but it could be confusing. Some users may not realize how many hits are really needed for some features.