TP Manual Calculation z,y,z

Hi guys,

Basically I'm measuring a bunch of parts for a capability study. Long story short I need to get true position on four similar features. For this instance I'm not sure how to accurately pull this off with the feature inside PC-DMIS since I'm trying to get it from 3 midpoints (1 in x, 1 in y, 1 in z). I figure I can use all the deviations and export the numbers into my excel and just formula it out. I would think the formula for a radius of a sphere would be the same for true position where TP would be the same as r. In that case r^2=x^2+y^2+z^2, or TP = SQRT(x*x+y*y+z*z). But on another forum post I saw, TP = SQRT(x^2+y^2++z^2)*2. What gives with the *2? They said that was for a circle? My shape is virtually a rectangular box. I don't understand how the middle of one object could be different from the middle of another object if it's "borders" were arranged differently?

Would, TP = SQRT(xdev^2+ydev^2+zdev^2), be the correct formula for getting TP on a rectangular box relative to called out datums?

Thank you guys!

frop1 over 9 years ago

Whoops.. just noticed title typo.
Cancel
Vote Up 0 Vote Down

Sign in to reply

Cancel
DaSalo over 9 years ago

True position is a bilateral zone. The formula you give will calculate the deviation in one direction so this is half of the true position value. Multiply by two to get the full width of the bilateral zone.
Cancel
Vote Up 0 Vote Down

Sign in to reply

Cancel
dph51 over 9 years ago

DaSalo, I think you mean it is a bidirectional tolerance zone.

In frop1's case, each axis should have a bidirectional zone defined (x,y,z).

Each needs to be reported.
2*Xdev
2*Ydev
2*Zdev

His formula SQRT(Xdev^2+Ydev^2+Zdev^2) = RADIUS of a spherical tolerance zone.
Cancel
Vote Up 0 Vote Down

Sign in to reply

Cancel
DaSalo over 9 years ago

Yep, what dph51 said.
Cancel
Vote Up 0 Vote Down

Sign in to reply

Cancel
frop1 over 9 years ago

Each needs to be reported.
2*Xdev
2*Ydev
2*Zdev

Would this mean I should be doing,
TP = SQRT ( (2*xdev)^2 + .. + .. )

Thanks for helping. I'm just trying to provide accurate information.
Cancel
Vote Up 0 Vote Down

Sign in to reply

Cancel
Nano Vujkovic over 9 years ago

DaSalo, I think you mean it is a bidirectional tolerance zone.

In frop1's case, each axis should have a bidirectional zone defined (x,y,z).

Each needs to be reported.
2*Xdev
2*Ydev
2*Zdev

His formula SQRT(Xdev^2+Ydev^2+Zdev^2) = RADIUS of a spherical tolerance zone.

Maybe you meant to say diametric tolerance zone vs radial tolerance zone.
Cancel
Vote Up 0 Vote Down

Sign in to reply

Cancel
DaSalo over 9 years ago

The standard equation for 3D true position is: 2*Sqrt((X2-X1)^2+(Y2-Y1)^2+(Z2-Z1)^2)

Your initial equation gives you radial deviation while this gives diametric deviation.
Cancel
Vote Up 0 Vote Down

Sign in to reply

Cancel
dph51 over 9 years ago

FROP1,

what does our FCF or DRF callout the tolerance zone?

DIAMETRICAL
SPHERICAL
or bidirectional?
Cancel
Vote Up 0 Vote Down

Sign in to reply

Cancel

Nano Vujkovic over 9 years ago

Ø is a symbol for dimeter

FCFLOC2 =POSITION : DATUM_B
            FEATCTRLFRAME/SHOWNOMS=NO,SHOWPARAMS=YES,SHOWEXPANDED=YES
            CADGRAPH=OFF,REPORTGRAPH=OFF,TEXT=OFF,MULT=10.00,ARROWDENSITY=100,OUTPUT=BOTH,UNITS=IN
            COMPOSITE=NO,FIT TO DATUMS=YES,DEV PERPEN CENTERLINE=ON,OUTPUT ALIGNMENT=Datum Reference Frame
            CUSTOMIZED DRF=NO
            STANDARDTYPE=ASME_Y14_5
              SIZE TOLERANCES/1,DIAMETER,2.0866,0.0018,0
              PRIMARY DIMENSION/POSITION,[B]DIAMETER[/B],0.01,MMC,<PZ>,<len>,C,A,MMC,<size>,<dat>
              SECONDARY DIMENSION/<Dim>,<tol>,<MC>,<dat>,<dat>,<dat>
              NOTE/FCFLOC2
            FEATURES/DATUM_B,,

frop1 over 9 years ago

My superior, at work, told me what he wanted. I am still confused by all of this but I'll do as instructed. He told me it should apply in one direction only. I don't like bugging that boss. I'll just listen so I can finish by tomorrow.
Cancel
Vote Up 0 Vote Down

Sign in to reply

Cancel