Datums order of importance

[[Ca...]]

Do datums order of importance start with A then B then C,.. etc.?

I have a cylindrical part that is datum A and a flat face at the end that is datum B. In calypso base alignment do I set A as  rotation in space and origin A? Where does B go, or do I set B as rotation in space and origin A?

 

Datums A and B control the same leveling orientation.

QA_005877.pdf

[[na...]]

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No, the letter sequence tells you nothing, what is important will be stated inside Feature Control Frame and it's compartments (for example |ToP|Ø 0.3|G|D|T| ). The left most in FCF is G and will lock all degrees of freedom it can, what's left will lock D, what is left will lock T.

If you are worried you have to match Datum Reference Frame with part alignment-you don't have to.

Datums are positioned badly so many times, that I just do base alignment to features that are the most stable.

Edited Thursday at 05:49 AM

[[Da...]]

I would use cylinder A as Rotation in space. Plane B as Planar Rotation. Then set X,Y and Z according to the way you have it orientated on the CMM.

[[Ma...]]

Just note.

I would use any feature which is dominant in size as main, if you need then another dominant feature for stopping rotation.

You can use cylinder as main as David stated, but if it's big diameter and short length, then i would use plane as main feature.

And if you can - avoid using cylinder and spheres as alignment datum feature. Rather use 2 circles used in 3d line. Thank me later :-)