I installed an ER-25 collet chuck into a 2MT spindle, and chucked a 3/8" gage pin to check runout at the business end. The collet chuck claims 0.0002" concentricity.
The spindle, on it's outside, measures about 0.0002" TIR.
The gage pin, installed an a different ER-32 chuck also measures about 0.0002" or better.
I was disappointed to observe a TIR of about 0.0025" midpoint on the gage pin's stick out of 1" or so.
Thinking maybe I have a crappy ER-25 3/8" collet, I tried a few others (with different gage pins); same thing. Tried a different collet nut; same thing.
Then I tried something I didn't think would make much difference but, in the interest of beating myself up thoroughly, I marked the spindle and the chuck with a sharpie and proceeded to install the chuck at 90, 180 and 270 degrees.
At 90 degrees, TIR moved up to mid three thou . At 180 degrees, TIR moved to just under a thou . At 270 degrees, TIR moved to 2 ten thou .
I don't have a test indicator presently so I can't check the inside of the spindle's concentricity. Regardless, can a chuck's insertion point in a tapered spindle affect terminal runout as I described? If so, is there a faster, better way to converge on the ideal insertion point? I only tried 4 points, hate to have to try 360 of them, lol.
The spindle, on it's outside, measures about 0.0002" TIR.
The gage pin, installed an a different ER-32 chuck also measures about 0.0002" or better.
I was disappointed to observe a TIR of about 0.0025" midpoint on the gage pin's stick out of 1" or so.
Thinking maybe I have a crappy ER-25 3/8" collet, I tried a few others (with different gage pins); same thing. Tried a different collet nut; same thing.
Then I tried something I didn't think would make much difference but, in the interest of beating myself up thoroughly, I marked the spindle and the chuck with a sharpie and proceeded to install the chuck at 90, 180 and 270 degrees.
At 90 degrees, TIR moved up to mid three thou . At 180 degrees, TIR moved to just under a thou . At 270 degrees, TIR moved to 2 ten thou .
I don't have a test indicator presently so I can't check the inside of the spindle's concentricity. Regardless, can a chuck's insertion point in a tapered spindle affect terminal runout as I described? If so, is there a faster, better way to converge on the ideal insertion point? I only tried 4 points, hate to have to try 360 of them, lol.