Another instance of my programmer and I butting heads. First off, I want to ask... Is an alignment needed to measure the concentricity of 2 circles? If so, can a proper alignment be made with paint on the plane that we are leveling the part to? He says that even with paint (very uneven paint) on the part, the concentricity will be accurate. Again, be gentle.
dph51, you are correct!!! ASME dosen't really recognize concentricity. Concentrecity is abroad and abuse call-out by many. what many folks may be looking its position.
with ISO the story may be different...
ISO use to differ concentricity (2D) and "Coaxiality" (3D).
If you look at ISO1101, you can see that concentricity is defined only for 2 coplanar circles, so in the same cut plane.
An easy way to check value is to create a local alignment on the datum, and dimension the polar radius of the feature : no hidden method calculating !
As concentricity is basically two centre points measured on the same working plane if the plane is levelled to the datum required then the result of the two circles
centres are projected over each other. The result given is also relevant to the working plane if slightly skewed the distance the circles are apart will accentuate the error.
On cylinders the result has a length these need to be perpendicular and I personally would not use them as there can be more error.
Concentricity due to the reasons I have given is why most drawings call out True position now as it was prone to alignment skew error.
I would suggest you need an alignment to measure accurately in the first place. I only report conc as cylinder to cylinder as that is how I understand it should be used. The alignment comes from your reference feature when you construct it. I use runout for just a circle where possible. (I am a newbie).
dph51, you are correct!!! ASME dosen't really recognize concentricity. Concentrecity is abroad and abuse call-out by many. what many folks may be looking its position. with ISO the story may be different...
I think what is usually really needed is
runout. position calc's the location of the
axis of a circle, runout measures whats going on on the
surface of a circle. I hope pcdmis knows the difference...
You don't need an alignment to measure circles for concentricity? That seems couterintuitive to me. Aren't circles 2D features that are reliant on the workplane and alignment they are measured from? With no alignment, wouldn't you be dependant on the part being perfectly square with the machine axis? And the circles being exactly perpedicular to the probe?
This was my first thought as well.
The cmm needs to know how the part sits before it can decide how to report it.
This was my first thought as well. The cmm needs to know how the part sits before it can decide how to report it.
Yeah - just because you don't specify what you are leveled on doesn't mean you aren't leveled on something anyway! But what would it be? Maybe not what makes sense... Your circle may look like an ellipse to pcdmis.
If you consciously level on something then you know for sure which way is up!
