I can't think of any political contributions for the group right now, so I'll post something on topic.
I use set screw type tool holders. I have TG and ER type collet chucks but I don't use them much. A lot of people disagrees with me, but I have found them to often have worse run out than "standard" tool holders.
I have a job coming up where I'll be running small cutters (1/32") in a material (copper) that cuts best at high SFM (600+). So I'll be using a high speed air spindle in the main spindle to get the RPM I need.
The air spindle is mounted with a straight shank on one end and uses a tiny collet to hold the end mill. I measured the run out on a tool and it is close to .001", which is not real great on a .031" tool, but is workable. I then measured the total run out between the tool axis in the air spindle and the main machine spindle and found the TIR was .005" which is high enough to put features cut with that tool out of spec.
This got me thinking. So I measured the run out on a few set screw tool holders and they're all around .002 TIR. Makes sense, there is about .001" clearance between the tool and the holder, and it is all pushed to one side, hence .002 TIR. Not too good, but at least it doesn't effect positioning accuracy of features in a part because the developed tool diameter is still concentric to the axis of the mill. It just wobbles a bit.
The problem is when you're cutting something without turning the mill spindle, like when you're using a high speed air spindle attached to a tool holder with run out. Your coordinate system could be off a few thou, which, in this case, is enough to mater so must be compensated for either in a work offset or perhaps I'll turn an eccentric sleeve to get everything in line.
Anyway, I know a few of you use these high speed attachments, and perhaps hadn't considered that some may not be perfectly in line with your spindle axis. A good quality attachment on a dedicated tapered shank will probably not exhibit any problems, but my setup does.
I have three mills in my shop, all with different tapers, so a straight shank tool seamed like a good idea at the time, but now it is adding up to more unproductive work getting it in line.