i needed an er16 collet chuck for my stepper motor.
purchased two from ebay: "er16 collet chuck motor extension"
i've had much luck with chinese tools, but this time... it was a terrible experience.
the specs said if i purchased 8mm ID for motor shaft, I would receive 7.98mm shaft so i could induction heat it, then put it on the shaft
however, i recieved 8.1mm oversized hole, so i couldn't use it... too much runout.
took over a month for it to arrive, wasn't going to wait again.
based on google and forums er collet chucks have 8 degree internal taper angle
my compound was not gonna have the accuracy required,
so i used a bevel protractor to get the precision within 0.1 degrees, which for ER collets is enough
even greater precision could be set, if i purchased electronic bevel protractor, but it would cost me over $600 for quality one.
i just went with vernier one, which wasn't too bad.
below is the link to the making vid of this collet holder
feel free to comment