After finishing to length and measuring with some large digital calipers I was satisfied that I was pretty close. My guess at that point was I was within a grand (.001) of the target dimension. Now just to give you all the information these calibration rods are around a foot long and a half inch in diameter. A 5C collet has maybe an inch of gripping length for that half inch diameter. I was not spinning the part particularly fast maybe 800-1000 rpm. Something I have noticed in CNC lathes with longer parts stuffed into the headstock is part whip and how it effects the different lathe operations. Part whip can show up at unexpected times related to gripping pressure and the resonant frequency of the unsupported part in the headstock. Most times its not a real big problem but occasionally the planets align and you see some of the negative effects manifested in your parts.
So I trotted off to the inspection department to see how well I did with my lowly calipers and a light touch.
How could I have done better? Well in hindsight I might have made a little plastic bushing to fit the ID of the headstock that supported the rod concentrically. Collet clamping pressure may have played a part here. I reset the pressure part way through facing the rods. This was because I didn't lock the tightening mechanism (lazy) on the collet closer which I of course bumped causing me to need to reset the pressure. Spindle speed could have been much slower and still produced a good finish. I'm hardly likely to calculate the critical speed for every part that sticks into the headstock. So who is to say I wouldn't land on another resonant frequency. I might have used a chuck instead of the collet because of its much longer gripping surface. Any chuck runout is not a problem because I was trying to make a surface perpendicular to the rotational axis. If the chuck did not grip the part parallel with the spindle axis I might produce a surface like Bob measured. Hmmm, something else to check on the Hardinge. Collet might be junk also. Half inch collets get used quite a bit. Another thing to check.
Hindsight is obviously pretty good so what could I have done to check it in the shop with normal tools and gages a machinist might have readily at hand? I think I would start with measuring it in the machine with a test indicator. In fact I think I will do it just to see what is visible rotating it by hand with a sensitive indicator on it just for my own satisfaction. There should be no whip with hand rotation and I would be comparing the runout of the OD in a couple of places with the end face. This might expose what Bob found on the CMM inspection.
So at first glance what looks like a no brainer part has all kinds of problems. Its always the easy ones that come back to bite you. Not very much error in the grand scheme of things but what if it had to be dead nuts? So the moral of this story is, Trust but verify.
I will post an update on what I discover when I measure the parts on the machine.