Hi Guys, Question on Datum Feat

[Rwelch9]

Hi Guys,

Question on Datum Feature Simulators.

Almost all of the parts we machine have very decent form , so i have never used a vice / fixture or ground plate etc as a simulator.

i have always took my references features from the actual part itself . Example take 12 points on the top face of my component and set ref .

Is my approach to inspection wrong and more specifically my approach to Datum feature simulators wrong.

I should be working to ASME Y 14.5 standards , although very new to this concept of working.

Thanks

 

[drawoh]

Rwelch9,

Let's look at ground plates. You have a ground plate. Your primary datum feature is a flat bottom face. You sit this on your ground plate. You take measurements either with a height vernier, or with dial indicators you calibrated with gauge blocks. The ground plate simulates your primary datum.

Are you using a CMM?

--
JHG

 

[Rwelch9]

drawoh,

Yes CMM , am i wrong in using the CMM as Datum simulator. ?

I understand the concept of using ground plate etc, just always thought if my face has good form etc that using the CMM as a simulator is ok.

Would i be wring on this ?

 

[drawoh]

Rwelch9,

I am not very familiar with CMMs.

You need to rigidly position your part with respect to the CMM, and then locate the datum features. Your part cannot move once the datum features are detected. If your primary datum is a flat face with nothing sticking out, you can detect the top of the granite block it is sitting on. Otherwise, you must detect the face itself.

--
JHG

 

[3DDave]

If you use physical datum simulators you can more rapidly inspect the parts by first establishing the theoretical datum simulators from the physical datum simulators and then just placing each part to be inspected against them.

This doesn't apply when the acceptable tolerances are very close to the expected variation; that situation would require better equipment than you may be using.