Holding ±0.0002 on a 0.7500 Ti‑6Al‑4V slip fit for flight hardware and my bore mic feels like guesswork; thinking bench air gage with ring masters. Do you see better repeatability long-term with Mahr vs Federal/Mitutoyo at 68°F over a 10‑hour shift, and how fussy are they about a trace coolant film and 16 Ra?
And ran that 0.7500 Ti slip fit on a Mahr column with a 2‑jet plug and held ±0.00005 all day once we controlled air and wiped parts. > at 68°F over a 10‑hour shift, and how fussy are they about a — Mahr drifted less than Mitutoyo as the room crept 1°F; a thin coolant film reads +0.0001–0.0002 unless you hit it with IPA. Feed clean, dry 25–30 psi and check both ring masters at start/mid‑shift — are your bores truly 16 Ra after finish?
In my shop, Mahr vs Mitutoyo repeat about the same; over a 10‑hour shift at 68°F the drift is almost always the air and the masters, which drives me nuts. Put a coalescing + desiccant filter and a fine regulator right at the bench, let the column warm 30 min, keep the ring master soaking there, and wipe the Ti with IPA — ‘trace coolant film lies by a few tenths’ — especially on 16 Ra. If your 0.7500 tends to lobing, a 3‑jet plug averages nicer; otherwise a 2‑jet is fine but fussier — do you have dedicated dry air to the gage?
@gradavi’s right on the air — mount a point‑of‑use regulator/coalescer (I add a mini desiccant) at the gage and park the ring and plug there to equalize; once I did that, Mahr and Mitutoyo repeated the same and a quick IPA wipe kept Ti’s coolant sheen from reading minus — do you have a dry drop at the stand?