True Concentricity Gauge?

[Jinx-)]

I'm looking at available concentricity gauges and so far I haven't seen one which can measure it. But what I see even when they called concentricity gauge, they are nothing but runout gauges, but then why not call them runout gauges and stop confusing people with concentricity, because ellipse, square, hexagon, etc they all can be concentric and to measure concentricity 2 readings are required 180 degrees apart sort of like this..

[Mikecr]

I agree that runout is not the same as concentricity, and that too many tools are merchandised incorrectly.
As to confusion; You state that any shape can be concentric(centered), I agree. Yet you contend that an outside 180deg comparison is required to measure it.
Well, how would your indicators subtract to leave only eccentricity, if opposing sides are not the same distance from your center?

I contend that w/resp to your method of measure, concentricty is qualified only with diametric stock (lathe turned, etc).

[Jinx-)]

Well there are true concentricity gauges for the price 10X what they sell to reloaders here is one example.



basically for a circle 3 points are required to triangulate its center and concentricity requires deriving the median points of the feature. So, the concentricity tolerance zone is cylindrical and controls the center of the feature.

[Mikecr]

But with all measurements, like math, something must be given (qualified).
What's given in the 10x measure above is that the piece is symmetric, and straight. With these qualified, then concentricity can be determined with it. Makes sense.

But cartridge cases are not machined. They are not symmetric, diametric, or straight.
Nothing is given with them.
An example would be like Rx1.2+W = .0017" (which means nothing at all).

So your 10x device above would indicate nothing but runout on cartridge cases.

[Trickymissfit]

Originally Posted by Jinx-)

Well there are true concentricity gauges for the price 10X what they sell to reloaders here is one example.



basically for a circle 3 points are required to triangulate its center and concentricity requires deriving the median points of the feature. So, the concentricity tolerance zone is cylindrical and controls the center of the feature.

what brand is that unit? I've seen similar units, but three times larger. I've even seen one similar that used a roller setup to measure run out off encoders. That one was fully automated and built into a parts straitening affair. I still like the old time cast iron bench centers, but most are too big.
A NECO will do most of what we see in the photo, but I really do like their setup. (right kind of indicators with three working together)
gary

[boomtube]

"Well there are true concentricity gauges for the price 10X what they sell to reloaders here is one example."

It seems you already know the answer to your question and, if so, you know you're beating a dead horse because no one else cares about the technical definitions. And "concentricity" is certainly no more incorrect than what commonly passes for 'neck tension' instead of bullet grip.

[Jinx-)]

Yeah dead horse it is, all we care is runout, but concentricity is more complicated then taking indicator reading from one side and if you get no runout, then brass should be somewhat concentric.

Gary, they made by Universal Punch Corp Universal Punch Corporation concentricity gage