THEO vs. ACTUAL THICKNESS

[dfiola66]

I've been asked to do a mini gage r&r. The gage is not a cmm fixture, just a plain gage with nets and spring loaded tapered pins.

I have math data for the part, but not for the gage. So...I need to set up off the gage but need to use the part features to do so in order to check the features in car position.

To set up the plane, I'm taking 4 points on the net surfaces on the gage which is .8mm (stock thickness) lower than part (of course). Taking 4 surface points, do I use the THEORETICAL or ACTUAL thickness? Whats the diff?

TIA!

[Paul Sarrach]

If you are setting up nets, no thickness is needed on the nets. Click on net side of metal and flip vector.

[dfiola66]

If you are setting up nets, no thickness is needed on the nets. Click on net side of metal and flip vector.

That'd work too. I did figure out that using the THEO thickness, you must think of where the point you're measuring is to the point you're picking on the cad.

In my case, my point was minus from the cad, so I entered -.8mm THEO and it came out right.

But when I read your post Paul, I remembered I'd done it your way before. I rarely am required to do this type of stuff and I forget it real fast if I don't use it every day!

[Paul Sarrach]

I post for stuff I forget too. Its not like riding a bike

[Lawrence Hardtacke]

When using THEO with metal thickness, PC-DMIS moves the nominal along the vector and gives you the new updated NOMINAL.

When using ACTUAL with metal thickness, PC-DMIS internally moves the nominal along vector but does not change the Original Nominal.