Calibration in the Wrong?

[operator1]

I have a slight calibration issue. The CMM calibrates perfectly to the calibration probe, but does not calibrate to a boring gage set to 1.5743; it always shows undersized or oversized. Is this problem fixable? If so, how?

[John Kingston]

I wouldn't compare the CMM to a bore gage. How many hits are you taking on it? How do you know you are hitting perfectly on it? How far off? What is the capability of your CMM?
There are a number of variables that need to be looked at.

[Wingman]

WJS. Especially - how far off?

[JamesMannes]

Post the entire program into a posting here.

[operator1]

I wouldn't compare the CMM to a bore gage. How many hits are you taking on it? How do you know you are hitting perfectly on it? How far off? What is the capability of your CMM?
There are a number of variables that need to be looked at.

The CMM takes 3 rows of hits to make 3 circles; about 6 or 7 hits per circle.

The hits are relatively evenly spaced all around the part.

Everything else I'm not sure.
The boring gage is 1.5743, and the boring micrometer(or whatever you call it) calibrates to the boring gage just fine. My whole thing is: If the CMM measures a different number for a boring gage(which is precisely precise), how can I be sure the CMM is giving me the correct results?

[Wingman]

The CMM takes 3 rows of hits to make 3 circles; about 6 or 7 hits per circle.

The hits are relatively evenly spaced all around the part.

Everything else I'm not sure.
The boring gage is 1.5743, and the boring micrometer(or whatever you call it) calibrates to the boring gage just fine. My whole thing is: If the CMM measures a different number for a boring gage(which is precisely precise), how can I be sure the CMM is giving me the correct results?

Please do what James said. CMM's report what they get. They get what you tell them to get. They have some error but if you use them correct you can minimize this.

The thing is, you don't say what kind or error you are getting. And 6 or 7 hits per row doesn't sound like a precise pattern etc.

Please do what James says and post code.

[JamesMannes]

The CMM takes 3 rows of hits to make 3 circles; about 6 or 7 hits per circle.

The hits are relatively evenly spaced all around the part.

Everything else I'm not sure.
The boring gage is 1.5743, and the boring micrometer(or whatever you call it) calibrates to the boring gage just fine. My whole thing is: If the CMM measures a different number for a boring gage(which is precisely precise), how can I be sure the CMM is giving me the correct results?

I asked for a copy of your program for that exact reason. Your alignment and how the circles are measured are critically linked to the methodology used to align your part to the CMM.

Have you taken my/other peoples advice and created a manual alignment that locks down the 6° of freedom cited in the papers I gave you? And then did you do this in DCC mode?

[operator1]

=alignment/start,recall:, List= Yes
            Alignment/end
            Loadprobe/rick1
            Tip/t1a0b0, Shankijk=0, 0, 1, Angle=0
            Mode/manual
            Workplane/zplus
            Loadprobe/rick1
            Tip/t1a0b0, Shankijk=0, 0, 1, Angle=0
            Prehit/ 0.075
            Retract/ 0.055
            Check/ 0.4724,1
            Movespeed/ 80
            Scanspeed/ 5
            Fly/on,0.1181
            Workplane/zplus
            Mode/dcc
            Move/point,9.403,4.7804,-26.0703
            Move/point,9.6389,4.5946,-28.3462
Plane1     =feat/plane,rect
            Theo/9.387,4.5542,-28.7035,0.0004049,-0.0003886,0.9999998
            Actl/9.387,4.5542,-28.6997,0.0002327,-0.0003199,0.9999999
            Meas/plane,5
            Hit/basic,10.3705,4.716,-28.7039,0.0004049,-0.0003886,0.9999998,10.3706,4.716,-28.6999,use Theo = Yes
            Hit/basic,9.862,3.8501,-28.704,0.0004049,-0.0003886,0.9999998,9.862,3.8501,-28.7,use Theo = Yes
            Hit/basic,8.8631,3.8502,-28.7036,0.0004049,-0.0003886,0.9999998,8.8631,3.8502,-28.6998,use Theo = Yes
            Hit/basic,8.5182,4.8233,-28.7031,0.0004049,-0.0003886,0.9999998,8.5182,4.8234,-28.6994,use Theo = Yes
            Hit/basic,9.321,5.5315,-28.7031,0.0004049,-0.0003886,0.9999998,9.321,5.5315,-28.6993,use Theo = Yes
            Endmeas/
            Move/point,9.3206,4.775,-27.8987
Circle1    =feat/circle,rect,in,least_sqr
            Theo/9.3996,4.6063,-28.9924,0,0,1,1.5743
            Actl/9.4192,4.6209,-28.9924,0,0,1,1.5768
            Meas/circle,5,workplane
            Hit/basic,10.1814,4.697,-28.9924,-0.993331,-0.1152974,0,10.2036,4.6995,-28.9924,use Theo = Yes
            Hit/basic,9.4688,3.8221,-28.9924,-0.0878054,0.9961376,0,9.4676,3.8339,-28.9924,use Theo = Yes
            Hit/basic,8.6214,4.4888,-28.9924,0.9887999,0.1492472,0,8.6415,4.4919,-28.9924,use Theo = Yes
            Hit/basic,8.8771,5.195,-28.9924,0.6638055,-0.7479052,0,8.8755,5.1918,-28.9924,use Theo = Yes
            Hit/basic,9.9109,5.2049,-28.9924,-0.649424,-0.7604265,0,9.9266,5.2244,-28.9924,use Theo = Yes
            Endmeas/
            Move/point,9.4911,4.9548,-28.9825
Circle2    =feat/circle,rect,in,least_sqr
            Theo/9.3996,4.6064,-29.352,0,0,1,1.5743
            Actl/9.4192,4.6211,-29.352,0,0,1,1.5755
            Meas/circle,5,workplane
            Hit/basic,10.1829,4.6807,-29.352,-0.9955311,-0.094434,0,10.2046,4.681,-29.352,use Theo = Yes
            Hit/basic,9.7902,3.9227,-29.352,-0.4960448,0.868297,0,9.7855,3.9237,-29.352,use Theo = Yes
            Hit/basic,8.6354,4.4184,-29.352,0.9710249,0.2389783,0,8.657,4.4224,-29.352,use Theo = Yes
            Hit/basic,9.0814,5.3265,-29.352,0.4042207,-0.9146615,0,9.0761,5.3302,-29.352,use Theo = Yes
            Hit/basic,9.9153,5.2013,-29.352,-0.6550641,-0.7555733,0,9.9307,5.2203,-29.352,use Theo = Yes
            Endmeas/
            Move/point,9.4625,4.8422,-29.3522
Circle3    =feat/circle,rect,in,least_sqr
            Theo/9.3996,4.6067,-29.76,0,0,1,1.5743
            Actl/9.419,4.6213,-29.76,0,0,1,1.5754
            Meas/circle,5,workplane
            Hit/basic,10.1866,4.6036,-29.76,-0.9999922,0.0039426,0,10.2064,4.6014,-29.76,use Theo = Yes
            Hit/basic,9.7917,3.9241,-29.76,-0.4980471,0.86715,0,9.7872,3.9249,-29.76,use Theo = Yes
            Hit/basic,8.6697,4.3118,-29.76,0.9272035,0.3745579,0,8.6913,4.3197,-29.76,use Theo = Yes
            Hit/basic,8.9327,5.2401,-29.76,0.5934024,-0.8049059,0,8.9297,5.2385,-29.76,use Theo = Yes
            Hit/basic,9.8794,5.2311,-29.76,-0.6092803,-0.7929549,0,9.893,5.2504,-29.76,use Theo = Yes
            Endmeas/
            Move/point,9.4867,4.695,-29.7627
            Move/point,9.4867,4.6951,-26.8188
            Move/point,9.4867,8.7528,-25.1042
Point1     =feat/point,rect
            Theo/10.3996,4.6063,-28.9824,0,0,1
            Actl/10.4192,4.6209,-28.9924,0,0,1
            Constr/point,offset,circle1,1,0,0
Line1      =feat/line,rect,unbnd
            Theo/9.3996,4.6063,-28.9824,1,0,0
            Actl/9.4192,4.6209,-28.9924,1,0,0
            Constr/line,bf,2d,circle1,point1,,
Cyl1       =feat/cylinder,rect,out,least_sqr
            Theo/9.3995,4.6065,-29.3712,-0.000013,0.0005203,-0.9999999,1.5743,0.7783
            Actl/9.4191,4.6211,-29.3763,-0.0003899,0.0003382,-0.9999999,1.5759,0.7683
            Constr/cylinder,bf,circle1,circle2,circle3,,
A1         =alignment/start,recall:, List= Yes
            Alignment/level,zplus,plane1
            Alignment/rotate,xplus,to,line1,about,zplus
            Alignment/trans,xaxis,cyl1
            Alignment/trans,yaxis,cyl1
            Alignment/trans,zaxis,
            Alignment/end
Dim Loc1= Location Of Cylinder Cyl1  Units=in ,$
Graph=off  Text=off  Mult=1.00  Output=both
Ax   Nominal     +tol       -tol       Meas        Max        Min        Dev      Outtol   
X      0.0000     0.0005    -0.0005     0.0000     0.7874    -0.7775     0.0000     0.0005 ----#----
Y      0.0000     0.0005    -0.0005     0.0000     0.7091    -0.7873     0.0000     0.0005 ----#----
Z    -29.3692     0.0005    -0.0005   -29.3755   -28.9914   -29.7596    -0.0064     0.0069 <--------
D      1.5743     0.0005    -0.0005     1.5759     1.5771     1.5753     0.0016     0.0011 -------->
H      0.7783     0.0005    -0.0005     0.7683     0.7683     0.7683    -0.0100     0.0105 <--------
End Of Dimension Loc1

[cmmguy]

What is it that you are measuring?
Is it a master of some sort or a actual part?

[operator1]

What is it that you are measuring?
Is it a master of some sort or a actual part?

The part is called an Idler Pulley, and I'm checking the inside diameter of a bored hole.




By the way, I didn't write the program. Someone else did. And we're using a completely different probe tip from before(but it calibrates fine).

But the program I created with the other tip (a 3by20) did the exact same thing.

There's a program for the ring gage. Did you need that too?

[operator1]

And yes, the alignment is done in Mode DCC.

[Wingman]

And yes, the alignment is done in Mode DCC.

Unless something posted incorrectly or I am missing something your alignment is not done until after you measure your features.

When I want to repeat a bore gage measurement I set the machine to a ring gage. But, to get closer numbers you might want to consider measuring a Cylinder and setting algorythm to MAX Inscribe. A cylinder is not susceptible to alignment error like a circle is. Be mindful of shanking.

Also remember, a CMM ID (MAX Inscribe) is based on three points. Dial Bore Gage is based on two. CMM will come closer to an Intramic (3 points) but even there may be form error unless you are talking about a Calibrated Ring Gage. If you are measuring a Ring Gage your values should be MUCH closer than you reported. I would expect a few tenths.
Just some thought.

[operator1]

Unless something posted incorrectly or I am missing something your alignment is not done until after you measure your features.

No, you're not missing anything. He put the alignment at the end of the program. He did the same thing for the program that checks the ring gage.

[cmmguy]

The part is called an Idler Pulley, and I'm checking the inside diameter of a bored hole.




By the way, I didn't write the program. Someone else did. And we're using a completely different probe tip from before(but it calibrates fine).

But the program I created with the other tip (a 3by20) did the exact same thing.

There's a program for the ring gage. Did you need that too?

With regular parts (not masters), it is always possible to get variation between a CMM and a Boregage. The geometry variation (out of round condition) will cause the different results. Bore gages are the most accurate method for non-lobed features. CMMs will give you close results but are more about feature location not size. The different methods of calculation (LSQ/MIC/etc...) can affect the results also.

When compared on a ring gage, then the variation you see is probing and machine caused.

Regarding the alignment, do that before remeasuring the bore, nto before the dimension only.

[dwade]

Always level any ring gage or master to the ID and not the face of the part. Do as the others have stated, make manual alignment, then DCC, then measure you bore where you want. Use prime numbers for your bore measurement, not really necessary but I have heard that the software calculates diameters better with prime numbers for the hits taken.

Just my .02.

Duane