SM Concentricity
DanO measured <.002 runout on his new mandrels. For ground parts I cannot imagine why the runout would be more than a tenth or two if any at all.
Oops, I just noticed that was including the collet runout.
In my experience, ground parts like these come out pretty much dead nuts.
Robin Snyder
Robin, if you ground all the surfaces (shank, bushing and thread face) at the same time then yes, they should all be deadballs. More then likely they were rechucked a couple times. This should not add any real inaccuracy but it does compound somewhat. A decent lathe man should be able to do this. If its done on a CNC then its that much easier, the grinding of the carbide should be a piece of cake.
I have no idea what the problem could be or even if there is one. Obviously, the guy who says there is a gap when he puts the 2 pieces together has a problem. It could be simply that the thread mating face needs to be ground perpendicular to the thread/shank. Hard to say without actually holding them. As long as the thread is concentric and true to the shank everything else should fall in line.
I see someone else said they couldn't get the pins to go in. I find that somewhat likely. Just like you have taps from H0 to H5, same would go for the pins. The tighter the tolerances on the mandrels, the tighter the pins will fit.
I can give you a quick way to check the concentricity.
Chuck up the mandrel, spin and get the TIR (Total Indicator Reading)
Loosend the chuck and turn the mandrel 90 degrees.
Tighten the Chuck with the same pressure each time
Get the TIR again
Do this again until you have 4 readings (more if you like)
The differences in the readings would be the total runout. Obviously this isn't absolutely deadballs accurate but it will be pretty close. If the total difference is say .0005 I'd say you're good. If the diff. is something like .006 I would think that was too much.... you'd be .003 off center. I have a hard time seeing .003 any more but I sure can feel it.
Not sure if any of this helps but free advice is what its always been.
B