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Constructing a circle from a cone and dimensionning the circularity

JEFMAN
I need to dimension the circularity of a circle constructed from a cone, at a given height.
I think that measuring the circle cannot give an accurate result, because of the drift.
So I measured 2 circles around the given height,with the same number of hits and the same direction, and extract the center ball hits in a loop : 

ASSIGN/TIP_RAD=PROBEDATA("Diam")/2+PROBEDATA("prbrdv")
PL1 =GENERIC/PLANE,DEPENDENT,CARTESIAN,
$ NOM/XYZ,<0,0,15>,
$ MEAS/XYZ,<0,0,15>,
$NOM/IJK,<0,0,1>,
$ MEAS/IJK,<0,0,15>
ASSIGN/V1=PL1.IJK 
ASSIGN/V2=PL1.XYZ
V10=LOOP/START,ID=YES,NUMBER=CIRC1.NUMHITS,START=1,SKIP=,
ASSIGN/V12=CIRC1.RAWHIT[V10].XYZ
ASSIGN/V13=CIRC2.RAWHIT[V10].XYZ
ASSIGN/V14=CROSS((V12-V13),CROSS((V12-V13),ALIGN_1.ZAXIS))
ASSIGN/V15=V12+V14*TIP_RAD
ASSIGN/V16=V13+V14*TIP_RAD
ASSIGN/V17=UNIT(V15-V16)
ASSIGN/V5=V15-V2
ASSIGN/V6=DOT(V5,V1)
ASSIGN/V7=CROSS(V1,CROSS(V17,V1))
ASSIGN/V8=SIN(DEG2RAD(90-ANGLEBETWEEN(V1,V17)))
ASSIGN/V9=V2+V5-V6*V1-DOT((V6/V8)*V17,V7)*V7
PT1 =GENERIC/POINT,DEPENDENT,CARTESIAN,
$ NOM/XYZ,<V9.X,V9.Y,V9.Z>,
$ MEAS/XYZ,<V9.X,V9.Y,V9.Z>,
$NOM/IJK,<V17.I,V17.J,V17.K>,
$ MEAS/IJK,<V17.I,V17.J,V17.K>
LOOP/END

Then I construct a circle from PT1[1..CIRC1.NUMHITS] and I get a diamter, a center and a circularity. I noticed that the diameter is close to the diameter constructed from a cone (classical method), but the center moves of some µm (same order than the circularity...)

Note :
V12 and V13 are the center ball of each circle hit
V14 is a vector perp to the line between both center ball (V12-V13) and the Z axis so it gives the ball compensation
V15 and V16 are compensated points

I used a little this code :
http://www.pcdmisforum.com/forum/pc-dmis-enterprise-metrology-software/pc-dmis-for-cmms/411816-pierce-point-using-variables
Parents
  • I follow what you mean by CMM drift. Your target Z value is 15mm, but it will increase and decrease when the diameter of the cone is larger or smaller (as probe is traversing normal to the cone's surface angle).

    What's more important for the design intent, roundness at specified height or size at specified height? or are they equally a priority?
    Taking hits above and below the 15mm, then producing all the vector and theo hits are simulating the form, but giving a very accurate diameter at the specified height.
    BUT true form at the height in my opinion can't be simulated, you need hits directly (or as close as you can) to the 15mm.

    Maybe you could use your manual method to obtain the most accurate diameter, but then use hit data from autocone (with a cut of cone hits as close to 15mm as possible) to measure form/roundness?
Reply
  • I follow what you mean by CMM drift. Your target Z value is 15mm, but it will increase and decrease when the diameter of the cone is larger or smaller (as probe is traversing normal to the cone's surface angle).

    What's more important for the design intent, roundness at specified height or size at specified height? or are they equally a priority?
    Taking hits above and below the 15mm, then producing all the vector and theo hits are simulating the form, but giving a very accurate diameter at the specified height.
    BUT true form at the height in my opinion can't be simulated, you need hits directly (or as close as you can) to the 15mm.

    Maybe you could use your manual method to obtain the most accurate diameter, but then use hit data from autocone (with a cut of cone hits as close to 15mm as possible) to measure form/roundness?
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