How to you make a 1/8" collet on a 1/4" shaft

Hi everyone,
I have not used this list in a while but when I did, I always got
great answers. I have a situation. My mill needs a faster motor. So
I rigged up a Dewalt Laminate trimmer motor to the top of my
drawbar. I connected a 1/4 in shaft to the motor which runs down the
drawbar hole(about 16" long). On the lower end (turret end) I
installed a part that houses two high speed bearings in which the
shaft runs through. Now sticking out the very bottom of the piece is
a 1/4" high speed shaft about 1-1/2" long which needs colleting.

The whole idea is so that I can CNC engrave using high speed engraver
bits. I need to some how attach an 1/8" engraver bit to the 1/4"
shaft. What I need (I think) is piece that has a 1/4 female collet
on one end and an 1/8 female collet on the other. It can not be more
that a couple of inches long. I have tried boring 1/4" and 1/8"
holes in some round stock and use set screws to attach to the shaft
and mount engraver bit. I works ok but it's very hard to get it all
true at 30,000 rpms!

Any thoughts or better yet can someone make me the part I seek?
Dean