precision watch maker's lathe

This is a precision watchmaker's lathe. It was made in Germany to exacting specs. It features a 90 piece collet set and a 5000 RPM 115 volt AC motor.
I recently purchased this lathe because it would come in handy with making the models that I build. It came with only one (1) collet. There was no problem though ....... so I thought.
I had, in my tool chest, for several years, a 90 piece set of jeweler's lathe collets that should fit into the spindle..... so I thought.
the length of the collets were the same. the angle of the collet at the nose of the collet were the same, ..... but the diameter of my collets are .312" or 5/16". This being a German machine, the bore is in metric dimensions. this meant that I had to ream the bore to fit the collets. Another problem, this being a precision tool, the bore of the spindle is hardened, so I couldn't use a reamer.
I slit a 5/16 brass tubing and inserted it into the spinning bore with valve lapping compound. It worked, but ever so slowly, I would have needed a month of Sundays to complete the job. So, I found a round diamond file in my toolbox and filed the bore out in no time.
The accuracy of the bore is not critical because the tapered end of the spindle and collet nose, sets the accuracy.
all 90 collets fit now and with the help of a sewing machine motor (5000 RPM) and my Variac speed control, I now have a handy addition to my tool chest.