Profile With No Datums

I have been told that Profile of a Surface with no datums attached to it is the same does thing as flatness since it is only controlling form, not form and location.

Yes if it is attached to only one, flat surface. My question is about multiple contours that are attached to eachother

I have not used legacy dimensions often, but you can set your own unilateral tolerances with the + and - tol can't you? If I recall a profile of .010 means ± .005.

Correct, but it does not allow you to do a unilateral profile for "form only." You get a popup error. I'm trying to understand what legacy "FORM ONLY" is checking. For example, does it check the entire profile as one continuous segment for form? If so, don't understand why it can't do unilateral.

What popup are you getting? I am not 100% certain on this, and I can't try it right now. But if you do form and location without any datums attached, and give it unilateral tolerances do your results match a formonly calculation without using the unilateral tolerance?

Legacy Form Only only allows an equally disposed bilateral tolerance. So when you type is 0.010 in the plus and 0 in the minus, it really means ±0.005. Form and Location allows bilateral and unequally disposed tolerances. 

Legacy Form Only only allows an equally disposed bilateral tolerance. So when you type is 0.010 in the plus and 0 in the minus, it really means ±0.005. Form and Location allows bilateral and unequally disposed tolerances. 

Thanks, that clears this up for me.

You don’t happen to know why this is, do you? In theory you should be able to put in a unilateral tolerance, right?

Lukas Frey said:

You don’t happen to know why this is, do you? In theory you should be able to put in a unilateral tolerance, right?

It's because the command was added back when "form only" meant just that - only the shape of the profile was considered, irrespective of size or location.

This behaviour was then changed in PC-DMIS 4.3 MR2 to bring things in line with the ASME Y14.5 2009 definition of profile, which always includes size (a setting was added to retain the old behaviour: PC-DMIS Help Center - 2023.1 (hexagonmi.com)).

The easiest way to do an unequal profile to no datums is to use the geometric tolerance command (or xactMeasure FCF dimensions in versions prior to 2020 R2).  However, if you still want to use legacy dimensioning, you will need to perform a 3D best-fit alignment to your points first and then use form and location - because you have aligned to the points you are essentially excluding the location.