A LITTLE PRUSSIAN BLUING WILL GO A LONG WAY, USE IT SPARINGLY.

PRUSSIAN BLUING WILL STAIN ANYTHING THAT IT TOUCHES, INCLUDING YOUR FINGERS.

A GOOD CLEANING AGENT FOR PRUSSIAN BLUING IS ISOPROPYL ALCOHOL. SMALL AMOUNTS OF ISOPROPYL ALCOHOL ARE AVAILABLE FROM ANY DRUG STORE, WHERE IT IS SOLD AS RUBBING ALCOHOL.

ISOPROPYL ALCOHOL IS FLAMMABLE, SO IT MUST BE USED WITH GREAT CARE.

WHEN USING THE BLUING TECHNIQUE, THERE ARE TWO GENERAL APPROACHES.

FOR METHOD NUMBER ONE, YOU PUT A LIGHT COAT OF PRUSSIAN BLUING ON THE TEST PART AND THEN USE THE BALL PLUG GAGE TO WIPE THE BLUING OFF.

THIS IS THE TECHNIQUE THAT IS USUALLY USED TO INSPECT BALL BEARING RACE WAYS.

FOR METHOD NUMBER TWO, WHICH IS SOMETIMES CALLED PRINTING, THE PRUSSIAN BLUING IS APPLIED TO THE BALL PLUG GAGE AND THEN TRANSFERRED TO THE TEST PART BY RUBBING THEM LIGHTLY TOGETHER. THIS PRINTING TECHNIQUE IS THE ONE THAT IS USUALLY USED FOR EVALUATING INTERNAL SPHERICAL SURFACES. WHEN USING THE TECHNIQUE OF TRANSFERRING PRUSSIAN BLUING TO THE TEST PART FROM THE BALL PLUG GAGE, IT IS HIGHLY RECOMMENDED THAT A SATIN FINISHED BALL PLUG GAGE BE USED.

A SATIN FINISHED SURFACE WILL HOLD A NICE EVEN, VERY THIN LAYER OF PRUSSIAN BLUING, WHILE THE USUAL SHINY, SLIPPERY LAPPED SURFACE, OF A STANDARD BALL, WILL HAVE A SPLOTCHY, THICKER LAYER.

AFTER THE SATIN FINISHED BALL PLUG GAGE IS VERY LIGHTLY COATED WITH PRUSSIAN BLUING, THE BALL PLUG GAGE IS PLACED INTO THE SPHERICAL CUP AND LIGHTLY RUBBED AND INDEXED.

IF THE BLUING HITS AT THE VERY TOP RIM OF THE SPHERICAL CUP, THEN THE SPHERICAL CUP IS SMALLER THAN THE BALL.

IF THE BLUING HITS AT THE VERY BOTTOM RING OF THE SPHERICAL CUP, THEN THE SPHERICAL CUP IS LARGER THAN THE BALL.

IF THE BLUING COVERS THE ENTIRE SURFACE OF THE SPHERICAL CUP, THEN THE BALL IS THE SAME RADIUS AS THE CUP.

IT IS VERY HARD TO MACHINE THE SPHERICAL CUP EXACTLY THE RIGHT RADIUS SO TOLERANCES ARE OFTEN SPELLED OUT IN THE PERCENTAGE OF THE SPHERICAL SURFACE THAT BLUES IN I.E. THE SPHERICAL SURFACE MUST BLUE INTO X.XXX DIAMETER BALL PLUG GAGE 80%.

ANOTHER APPROACH IS THAT THE SPHERICAL CUP MUST BE LARGER THAN ONE BALL SIZE AND SMALLER THAN ANOTHER. THE DANGER OF THIS TYPE OF TOLERANCING IS THAT THE SURFACE OF THE CUP MAY BE GROSSLY OUT OF SPHERICITY BUT STILL MEASURE GOOD.

USING THE TOLERANCING THAT THE BALL MUST BLUE INTO THE SPHERE A GIVEN PERCENT IS BY FAR THE BEST TOLERANCING APPROACH.