This all revolves around a Sherline mill, so it's tiny.
Mine came with some small collets and a 3/8" endmill holder that threads onto the spindle with a 3/4-16 thread.
The holder itself is just a threaded cylinder with a 3/8" bore, grub screw and holes for the tommy bars to tighten it onto the spindle, which also has a hole drilled though it for another tommy bar. No wrenches or anything like that are needed.
These were all made by Sherline and run true, no matter how I measure it. The OD of the holder wobbles less than 0.001 and if I try to measure the3/8" bore with an indicator on the shank of tightest endmill, it's barely wiggles the indicator pointer. This matches on the lathe or mill, so it's pretty consistent that is all lines up.
I just got some "A2Z CNC" stuff which as far as I can tell, is just junk. I have a quick change tool post from them which is iffy as well. It shipped with the wrong length screw, and the tool holders are quasi threaded through, where you need to chase the treads with a full out handle hex driver for the first use. It's just cosmetic, but a couple have that made from the end of a piece barstock look.
Both of the A2Z endmills holders wobble about 0.005" or more. The runout is clearly visible. The OD is better, but the bore is not concentric at all.
The threads are loose and the things wobble around on the spindle thread until you tighten them down. The Sherline holder has a firm fit, but never grabs or jams up.
One has deeper threads than the other too.
Anyways, this stuff is going back since it seems useless if it can't even match the accuracy of a drill chuck.
The question is are there rules of thumb for how much runout is acceptable for a small machine like this?
On another rant, I have a new no counry of origin marked 1/4" Jacobs drill chuck. It's horrible as well, it feels rough and can't be broken in. I'm guessing it's chinese and can't even be opened to polish the rough parts.
Every Rohm chuck I have is from and seems like a German machined product.
I have a real small 5/32 Yukiwa chuck which is also really nice.
Are all Jacobs drill chucks junk now?