GD&T and me

[Thomas Stewart]

Here's the short version...

I measure several diametrical features in the free state and a few areout of tolerance. So my boss suggested I get the fixture, clamp it down and remeasure those same features... I did and they were WAY out. Then I toleranced them in coordinate (XYZ)... The actual "measured" number was hugely different...

So the question is, How can it be that when I tolerance diametrical true position (MMC to the feature and -B- and -C-...) I get a substantially different number in simple axis tolerancing?

Okay that was the GD&T part... the ME part is it's driving me NUTS!!! Help if you can please...

[LynnA]

"How can it be that when I tolerance diametrical true position (MMC to the feature and -B- and -C-...) I get a substantially different number in simple axis tolerancing?"

Depends on what the Datum Structure is.
If doing True Postion at MMC, are -B- and -C- at MMC? What version PC-DMIS, how is part aligned, alittle more info, and someone can probably help ya out. There has been a lot "discussion" About GD&T here and in other places.

[Paul Sarrach]

Lynn is very wise in here second post. Welcome Lynn. It is the Datum scheme you are using. Do you have a pic of the scheme? Are you using CAD? What type of part? Stamping, Plastic ?
I can help you get nuttier, If you give us half a chance.

[bob mappes]

It may also (not knowing what this part is actually like) be that in a constrained condition the part shape has been altered.....?????

I have several parts that the notes say to apply things like flatness in a "constrained condition"

bob