Recently had the same challenge, to make up a line with double flare on each
end. Bought the tubing from local Canadian Tyre and borrowed their flaring
tool (cheap import type). Cut the tube square with a hacksaw, filed the end
dead square using the back face of the clamping bars as a guide, removed the
burr from inside of brake line, VERY IMPORTANT filed a healthy bevel on the
outside of the line, clamped the line using the clamp bolts THEN clamped
again in a bench vise, ran the die in, removed the die and ran in the cone.
Perfect first try.
Important points - no tubing cutters - work hardens the tube/pipe/line.
Dead square end, no burrs.
Large bevel on outer edge of line/pipe/tube.
Extra clamping.
A little lube - and good luck.

Try again, the kid will appreciate it, and you are his best teacher.
Ray
"mj" wrote in message
ps.com...
When you got to this line:

The tool looked brand new, but had the earmarks of being a cheap
import.

I knew then you were going to have problems without reading the rest.
I've never had luck getting a cheap import to work for flaring copper
tubing (especially double flares). I made the mistake of buying one of
these pieces of crap once. I had the same problem as you...the tubing
not staying put. I finally found a decent tool at work and that one
worked great.

Mike