Calypso - Form Datum

What the Form Datum does is establish a FUNCTIONAL Datum Reference Frame coordinate system, similar to if you were setting up the primary, secondary, and tertiary datums on a functional checking gage. This is ONLY for a datum reference frame and does not modify how the base and secondary alignments evaluate their respective coordinate system. In the screen shot below, you can notice the different origin points are for a base alignment and datum reference frame.

To set the Form Datum correctly click on Extras/ Settings/ Measurement/ Form Datum, check both the Outer Tangential Element and the Re. Calculation as per ISO 5459 boxes.

What is happening?

When we create our base alignment the alignment uses the intersection point of your features as below.

This is based on the measurement of the actual features of the part.

Form Datum uses the highest contact points that would touch a Datum Feature Simulator, in order of primary, secondary, and tertiary features, establish a real coordinate system. Calypso will establish the proper location through the form datum reference calculation per ISO 5459. Again this is ONLY used for a Datum Reference Frame and does not affect the Base Alignment.

Form Datum Applied.

As you can imagine this will affect your location and true position results.

Want to learn more

Bilateral Equal Tolerance - Calypso

A common question about profile is, if I take the minimum and the maximum values of my profile output they don’t add up to the profile results value. What is happening with the profile calculation?

Let’s look at one of the profile tolerance zone shapes.

Bilateral (Equal Distribution)

Let’s break down this picture above:

  

The black line is the Nominal Geometry.

The green line is the actual profile.

The blue lines are as designated, the upper and lower tolerance lines. Taking the blueprint tolerance and dividing that number by two, i.e. 0.10 is +/- 0.05 will assign the position of these lines.

  

The red lines are the actual reported profile deviation. This is where things won’t seem to add up. If my min is -0.0006 and my max is 0.0009 why is it not reported as 0.0015? Instead Calypso reports the profile as 0.0018. Calypso takes the point with the greatest deviation from the nominal geometry and doubles that result for the actual profile result.

Where A is the absolute value of either the min or the max the actual profile deviation = 2xA.

1.     Find the maximum value, or the largest deviation toward the outside of the part

2.     Find the minimum value, or the largest deviation toward the inside of the part

3.     A = The largest absolute vale of either the min, or max

4.     Reported Actual profile deviation = 2xA

Max:    .0009

Min:   -.0006

A = 0.0009

Profile Actual = 2xA = 0.0018

 NOTE FROM EDITOR: Although this article is focused on Calypso this formula is used in all softwares to calculate Bilateral Equal Distribution.

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