Planar Multiple Datums

[[Ma...]]

How would you accomplish the function of the datum simulator shown in Fig 4-22 in the attachment?

My parts are much larger, stiffer, heavier and more accurate than what is shown in the ASME example but have a similar stepped plane A-B primary datum.

Planar Multiple Datum.JPG

[[Ca...]]

Hi Mark,

The simplest suggestion would be to use an offset plane (found under Features - Special Geometries) you can take 2 points on 1 plane and 1 on another and offset the one point the basic distance (the 20 in this example). You can offset the points inside of the Evaluation Button.

To get more points on the surface, you could use point sets inside of point features then use recall feature points to pull the points into an offset plane. As a heads up, it is usually easiest to pull in the offset plane, go into Evaluation and add in the offsets, then use recall feature points to pull in the points.

[[Ch...]]

Definitely following this one. We had a similar callout come through recently.

Design says 2 mating offset surfaces will mate "at the same time".

I explored many options, would the method suggested by Caitlin above really cover the '3 highest points' though ?

Also there is a profile on them so they can float apart a bit - perhaps offset with actual distance ?

Love to hear others input as well.

I thought I used FFS as a primary once upon a time , doesn't seem to be an option in 2023.

What I suggested was : use Geo Best fit allow 2 rotations and 1 translation. Make a Theoretical Plane with this GeoBestFit alignment. Use this the plane as primary. Use either this or either of the 2 planes for your one axis origin (Z, etc).

We asked a GDT teacher that was on site, and he said just use either one as primary... I think that misses the intent.

May be a good case to request a new item in MyVoice portal

Thanks,

[[To...]]

How about a Geometry Best Fit Alignment of the 2 planes allowing 6 degrees of freedom (if Primary) with both set to Outer Tangential.

[[Ri...]]

If you have Calypso 2023 and like to try the new GD&T package, it can handle this with no issues.

For the Primary Datum, this is where you'd use the Common Datum option.

[[Ma...]]

Thanks for all the replies. We used the geometry best-fit as Tom recommended then created a theoretical plane in that alignment to use for the primary datum for characteristic evaluations. We'll check out the new GDT library next time we get a similar part.