Question about the small arc method

Hello all!

Please let me know if I am doing something wrong following the small arc method.

Btw, I am using vector points and auto circles with NO CAD always in DCC mode. Let's also assume that I am measuring in Z plane.

1) I am measuring the small arc with a fixed radius auto circle.
2) I am setting my origin XY to this circle.
3) Just to be sure I am repeating with a new auto circle fixed radius and realign to it.
4) I am taking 3 vector points in polar coordinates to be precise.
5) I am reporting the PR of the points.

This morning I had a 80deg on an arc R2.8mm to measure. I used this method and I was getting repeatable results at 2.80. The issue is that the radius has been measured to be 2.75mm (verified with 2 other methods also).

I also tried to change the fixed rad value based on the R measurement I had performed before with least squares (around 2.75 non repeatable value) and I was getting results close to that value (the least square value).

With this method, does the fixed Radius value provided alter the centre that is being found? Doesn't this beat the purpose of using this method?

Thanks in advance!

Parents

Don Meredith over 2 years ago

My method for measuring small arc is similar, except that I usually use six points. I need to measure the radius of the lining material on brake pads, which range from about 28 degrees to about 44 degrees.
First step is to construct an alignment at the center of the axle (the center point of the radius), then construct an Origin Point. My example is a radius of 169.0mm, so I create an Auto Vector Point at 0, 169.0, 15.5 with vectors of 0, 1, 0. My arc is 44 degrees on this part, so my starting point is rotated -22 degrees about Z-Axis. I copy the created point and Edit Pattern -22 degrees about Z and Paste 1 time. This is the first point of the six for my radius. I need 44 degrees evenly spaced, so 44/5 = 8.8. This is the rotation for the five additional points needed. Back to Edit Pattern, rotate +8.8 degrees five times, then copy the first point and Paste with Pattern. Now I have six points evenly spaced and the numbers for the last point should match the numbers for the first point, with the "X" and "I" values showing negative. The original Auto Vector Point is deleted.

The Measurement section:

RECALL/ALIGNMENT,INTERNAL,AL_HUB
P169A          =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
                THEO/<63.309,156.694,15.5>,<0.3746066,0.9271839,0>
                ACTL/<63.308,156.688,15.499>,<0.3746066,0.9271839,0>
                TARG/<63.309,156.694,15.5>,<0.3746066,0.9271839,0>
                SNAP=NO
                SHOW FEATURE PARAMETERS=NO
                SHOW CONTACT PARAMETERS=YES
                  AVOIDANCE MOVE=NO,DISTANCE=8
                SHOW HITS=NO
P169B          =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
                THEO/<38.591,164.535,15.5>,<0.2283509,0.9735789,0>
                ACTL/<38.65,164.798,15.499>,<0.2283509,0.9735789,0>
                TARG/<38.591,164.535,15.5>,<0.2283509,0.9735789,0>
                SNAP=NO
                SHOW FEATURE PARAMETERS=NO
                SHOW CONTACT PARAMETERS=YES
                  AVOIDANCE MOVE=NO,DISTANCE=8
                SHOW HITS=NO
P169C          =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
                THEO/<12.966,168.502,15.5>,<0.076719,0.9970528,0>
                ACTL/<12.965,168.479,15.499>,<0.076719,0.9970528,0>
                TARG/<12.966,168.502,15.5>,<0.076719,0.9970528,0>
                SNAP=NO
                SHOW FEATURE PARAMETERS=NO
                SHOW CONTACT PARAMETERS=YES
                  AVOIDANCE MOVE=NO,DISTANCE=8
                SHOW HITS=NO
P169D          =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
                THEO/<-12.966,168.502,15.5>,<-0.076719,0.9970528,0>
                ACTL/<-12.974,168.601,15.499>,<-0.076719,0.9970528,0>
                TARG/<-12.966,168.502,15.5>,<-0.076719,0.9970528,0>
                SNAP=NO
                SHOW FEATURE PARAMETERS=NO
                SHOW CONTACT PARAMETERS=YES
                  AVOIDANCE MOVE=NO,DISTANCE=8
                SHOW HITS=NO
P169E          =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
                THEO/<-38.591,164.535,15.5>,<-0.2283509,0.9735789,0>
                ACTL/<-38.577,164.476,15.499>,<-0.2283509,0.9735789,0>
                TARG/<-38.591,164.535,15.5>,<-0.2283509,0.9735789,0>
                SNAP=NO
                SHOW FEATURE PARAMETERS=NO
                SHOW CONTACT PARAMETERS=YES
                  AVOIDANCE MOVE=NO,DISTANCE=8
                SHOW HITS=NO
P169F          =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
                THEO/<-63.309,156.694,15.5>,<-0.3746066,0.9271839,0>
                ACTL/<-63.307,156.684,15.499>,<-0.3746066,0.9271839,0>
                TARG/<-63.309,156.694,15.5>,<-0.3746066,0.9271839,0>
                SNAP=NO
                SHOW FEATURE PARAMETERS=NO
                SHOW CONTACT PARAMETERS=YES
                  AVOIDANCE MOVE=NO,DISTANCE=8
                SHOW HITS=NO

The Calculation and Results:

DIM D169A= 2D DISTANCE FROM POINT P169A TO POINT PT_HUB     (CENTER TO CENTER),NO_RADIUS  UNITS=MM,$
  GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=NONE
  AX    NOMINAL       +TOL       -TOL       MEAS        DEV     OUTTOL
  M      169.000      0.500      0.500    168.994     -0.006      0.000 ---------#----------
  DIM D169B= 2D DISTANCE FROM POINT P169B TO POINT PT_HUB     (CENTER TO CENTER),NO_RADIUS  UNITS=MM,$
  GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=NONE
  AX    NOMINAL       +TOL       -TOL       MEAS        DEV     OUTTOL
  M      169.000      0.500      0.500    169.269      0.269      0.000 ---------------#----
  DIM D169C= 2D DISTANCE FROM POINT P169C TO POINT PT_HUB     (CENTER TO CENTER),NO_RADIUS  UNITS=MM,$
  GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=NONE
  AX    NOMINAL       +TOL       -TOL       MEAS        DEV     OUTTOL
  M      169.000      0.500      0.500    168.977     -0.023      0.000 ---------#----------
  DIM D169D= 2D DISTANCE FROM POINT P169D TO POINT PT_HUB     (CENTER TO CENTER),NO_RADIUS  UNITS=MM,$
  GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=NONE
  AX    NOMINAL       +TOL       -TOL       MEAS        DEV     OUTTOL
  M      169.000      0.500      0.500    169.099      0.099      0.000 -----------#--------
  DIM D169E= 2D DISTANCE FROM POINT P169E TO POINT PT_HUB     (CENTER TO CENTER),NO_RADIUS  UNITS=MM,$
  GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=NONE
  AX    NOMINAL       +TOL       -TOL       MEAS        DEV     OUTTOL
  M      169.000      0.500      0.500    168.940     -0.060      0.000 --------#-----------
  DIM D169F= 2D DISTANCE FROM POINT P169F TO POINT PT_HUB     (CENTER TO CENTER),NO_RADIUS  UNITS=MM,$
  GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=NONE
  AX    NOMINAL       +TOL       -TOL       MEAS        DEV     OUTTOL
  M      169.000      0.500      0.500    168.990     -0.010      0.000 ---------#----------
              ASSIGN/V169=(D169A.MEAS+D169B.MEAS+D169C.MEAS+D169D.MEAS+D169E.MEAS+D169F.MEAS)/6
R169         =GENERIC/CIRCLE,DEPENDENT,CARTESIAN,OUT,$
              NOM/XYZ,<0,0,0>,$
              MEAS/XYZ,<0,0,0>,$
              NOM/IJK,<0,0,1>,$
              MEAS/IJK,<0,0,1>,$
              RADIUS/169,V169
  DIM R_169= LOCATION OF CIRCLE R169  UNITS=MM ,$
  GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=BOTH  HALF ANGLE=NO
  AX    NOMINAL       +TOL       -TOL       MEAS        DEV     OUTTOL
  R      169.000      0.500      0.500    169.045      0.045      0.000 ----------#---------
  END OF DIMENSION R_169

Reply

Don Meredith over 2 years ago

RECALL/ALIGNMENT,INTERNAL,AL_HUB
P169A          =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
                THEO/<63.309,156.694,15.5>,<0.3746066,0.9271839,0>
                ACTL/<63.308,156.688,15.499>,<0.3746066,0.9271839,0>
                TARG/<63.309,156.694,15.5>,<0.3746066,0.9271839,0>
                SNAP=NO
                SHOW FEATURE PARAMETERS=NO
                SHOW CONTACT PARAMETERS=YES
                  AVOIDANCE MOVE=NO,DISTANCE=8
                SHOW HITS=NO
P169B          =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
                THEO/<38.591,164.535,15.5>,<0.2283509,0.9735789,0>
                ACTL/<38.65,164.798,15.499>,<0.2283509,0.9735789,0>
                TARG/<38.591,164.535,15.5>,<0.2283509,0.9735789,0>
                SNAP=NO
                SHOW FEATURE PARAMETERS=NO
                SHOW CONTACT PARAMETERS=YES
                  AVOIDANCE MOVE=NO,DISTANCE=8
                SHOW HITS=NO
P169C          =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
                THEO/<12.966,168.502,15.5>,<0.076719,0.9970528,0>
                ACTL/<12.965,168.479,15.499>,<0.076719,0.9970528,0>
                TARG/<12.966,168.502,15.5>,<0.076719,0.9970528,0>
                SNAP=NO
                SHOW FEATURE PARAMETERS=NO
                SHOW CONTACT PARAMETERS=YES
                  AVOIDANCE MOVE=NO,DISTANCE=8
                SHOW HITS=NO
P169D          =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
                THEO/<-12.966,168.502,15.5>,<-0.076719,0.9970528,0>
                ACTL/<-12.974,168.601,15.499>,<-0.076719,0.9970528,0>
                TARG/<-12.966,168.502,15.5>,<-0.076719,0.9970528,0>
                SNAP=NO
                SHOW FEATURE PARAMETERS=NO
                SHOW CONTACT PARAMETERS=YES
                  AVOIDANCE MOVE=NO,DISTANCE=8
                SHOW HITS=NO
P169E          =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
                THEO/<-38.591,164.535,15.5>,<-0.2283509,0.9735789,0>
                ACTL/<-38.577,164.476,15.499>,<-0.2283509,0.9735789,0>
                TARG/<-38.591,164.535,15.5>,<-0.2283509,0.9735789,0>
                SNAP=NO
                SHOW FEATURE PARAMETERS=NO
                SHOW CONTACT PARAMETERS=YES
                  AVOIDANCE MOVE=NO,DISTANCE=8
                SHOW HITS=NO
P169F          =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
                THEO/<-63.309,156.694,15.5>,<-0.3746066,0.9271839,0>
                ACTL/<-63.307,156.684,15.499>,<-0.3746066,0.9271839,0>
                TARG/<-63.309,156.694,15.5>,<-0.3746066,0.9271839,0>
                SNAP=NO
                SHOW FEATURE PARAMETERS=NO
                SHOW CONTACT PARAMETERS=YES
                  AVOIDANCE MOVE=NO,DISTANCE=8
                SHOW HITS=NO

The Calculation and Results:

DIM D169A= 2D DISTANCE FROM POINT P169A TO POINT PT_HUB     (CENTER TO CENTER),NO_RADIUS  UNITS=MM,$
  GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=NONE
  AX    NOMINAL       +TOL       -TOL       MEAS        DEV     OUTTOL
  M      169.000      0.500      0.500    168.994     -0.006      0.000 ---------#----------
  DIM D169B= 2D DISTANCE FROM POINT P169B TO POINT PT_HUB     (CENTER TO CENTER),NO_RADIUS  UNITS=MM,$
  GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=NONE
  AX    NOMINAL       +TOL       -TOL       MEAS        DEV     OUTTOL
  M      169.000      0.500      0.500    169.269      0.269      0.000 ---------------#----
  DIM D169C= 2D DISTANCE FROM POINT P169C TO POINT PT_HUB     (CENTER TO CENTER),NO_RADIUS  UNITS=MM,$
  GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=NONE
  AX    NOMINAL       +TOL       -TOL       MEAS        DEV     OUTTOL
  M      169.000      0.500      0.500    168.977     -0.023      0.000 ---------#----------
  DIM D169D= 2D DISTANCE FROM POINT P169D TO POINT PT_HUB     (CENTER TO CENTER),NO_RADIUS  UNITS=MM,$
  GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=NONE
  AX    NOMINAL       +TOL       -TOL       MEAS        DEV     OUTTOL
  M      169.000      0.500      0.500    169.099      0.099      0.000 -----------#--------
  DIM D169E= 2D DISTANCE FROM POINT P169E TO POINT PT_HUB     (CENTER TO CENTER),NO_RADIUS  UNITS=MM,$
  GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=NONE
  AX    NOMINAL       +TOL       -TOL       MEAS        DEV     OUTTOL
  M      169.000      0.500      0.500    168.940     -0.060      0.000 --------#-----------
  DIM D169F= 2D DISTANCE FROM POINT P169F TO POINT PT_HUB     (CENTER TO CENTER),NO_RADIUS  UNITS=MM,$
  GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=NONE
  AX    NOMINAL       +TOL       -TOL       MEAS        DEV     OUTTOL
  M      169.000      0.500      0.500    168.990     -0.010      0.000 ---------#----------
              ASSIGN/V169=(D169A.MEAS+D169B.MEAS+D169C.MEAS+D169D.MEAS+D169E.MEAS+D169F.MEAS)/6
R169         =GENERIC/CIRCLE,DEPENDENT,CARTESIAN,OUT,$
              NOM/XYZ,<0,0,0>,$
              MEAS/XYZ,<0,0,0>,$
              NOM/IJK,<0,0,1>,$
              MEAS/IJK,<0,0,1>,$
              RADIUS/169,V169
  DIM R_169= LOCATION OF CIRCLE R169  UNITS=MM ,$
  GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=BOTH  HALF ANGLE=NO
  AX    NOMINAL       +TOL       -TOL       MEAS        DEV     OUTTOL
  R      169.000      0.500      0.500    169.045      0.045      0.000 ----------#---------
  END OF DIMENSION R_169

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