# True Concentricity Gauge?

1. ### Jinx-)Well-Known Member

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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..

2. ### MikecrWell-Known Member

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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).

3. ### Jinx-)Well-Known Member

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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.

4. ### MikecrWell-Known Member

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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.

5. ### TrickymissfitWell-Known Member

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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

6. ### boomtubeWell-Known Member

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"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.

7. ### Jinx-)Well-Known Member

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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

8. ### TrickymissfitWell-Known Member

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another new brand name you hit me with! I've seen similar looking stuff, but with a hydrolock tail stock for measuring runout on bearing journals. Also use a similar design from Hamblin Gauge that is vertically mounted and has a probe system to relay feed back to the machine it measures parts off of. Reads all diameters in about thirty seconds and two parts later is back on size again (sometimes the next part)
gary

9. ### TrickymissfitWell-Known Member

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I have seen their stuff before! We had a couple of the silver ones at the bottom of the page. Never hit the floor with them, and were kept in the room with the master gauges and stuff. A real bear to calibrate all the steps at one time. I was tasked with getting masters ground to calibrate them. Made them from A2, and ground them before lapping them in to size. A really serious exercise on the use of Supermics! All TIR numbers were in arc seconds! The indicators were from Rhan, and later they went back to the analog versions as they didn't have to wait for the numbers to quit moving around.
gary

10. ### Jinx-)Well-Known Member

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Check this one from the same company and it only cost \$2,800.00 just a pocket change for average reloader and it only measures
projectiles, diameters and runouts at two locations. Measuring cycle time from part to part 12 second

here's another one to measure 20 - 30 mm projectiles it measures projectiles, diameters and runouts at two locations. Measuring cycle time from part to part 10 second. Project Cost \$4,700.00 complete.

11. ### sp6x6Well-Known Member

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Heres an observation. On my Sinclair style,dial up right. It read .003 off more?Than the Hornady lock and load style,dial behind,with adjuster to front.With this type you cant just check neck,have to have a bullet in,for larger neck size. Would not want to try pictured,just get more frustrated

12. ### Bart BWell-Known Member

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The best concentricity gage I know of is one made by me that cost less than \$2 in materials plus a cheap dial indicator.

Two 1/4" threaded rods 7 inches long with a V block at its back end for the case's pressure ring to ride in. Up front was a nylon washer held in the rods with a 3/8 inch hole in it. That washer's aligned such that its center is pretty much in line with .470 and .510 inch diameter case centers as they rest in the V block.

30 caliber rounds (.308 Win, .30-06 and two 30 caliber magnums) would be put in, back end resting in the V block and their shoulder pushed into the washer. That nylon washer could be moved back and forth so it puts the case pressure ring on the V block when the case shoulder's centered against it. Dial indicator plunger would be put about 1/10th inch back from bullet tip.

With the case's pressure ring resting in the V block and pushed forward seating its shoulder in the washer hole, that's how the case fits the chamber when it fires; its shoulder's centered in the chamber shoulder and the back end's pushed sideways against the chamber wall by the extractor. Any out of round caused by an oval- or egg-shaped case body at or near the shoulder doesn't effect the readings; full length sized cases ensure plenty of clearance between case body and chamber at the case shoulder.