"Andy McArdle" wrote in message
u...
If you do a bit of researching on the net you will see that you can make
a
vac chucking system with very little cost. Use an old freezer compressor
for
the vacuum and make a rotating joint with some sealed bearings - the ease
of
the rotating joint manufacture depends on what kind of outboard spindle
arrangement you have.
I used an old 2 piston rather large refrigeration compressor but bought
a
Oneway rotating joint. I made my own drum chucks out of ABS pipe
connectors.
Billh

For vacuum, high air-flow is better than high pressure. A household vauum
cleaner is sufficient, provided it has a by-pass valve to stop the vac
motor
from burning out from lack of airflow.

Depending on the lathe, a rotation joint is not necessary. A tin can can
do
the job! Mine is sized to fit over the handweel and secured to the
headstock with a disk of 1/2" ply, cut in half and drilled to fit closely
around the spindle. Oiling the spindle then applying a bead of silastic
around where the ply joins the spindle seals it enough for the vacuum to
work. (It's highflow, not high-pressure, remember.) A hole cut in the
other tin-can for the hose from the vac and voila!

It generates sufficient pressure to do light touch ups to the foot of a
bowl, careful removal of the tenon, reshaping, etc.

Even a commercial vac-chuck set up won't allow more than a light touchup
and
a tin can's a darn sight cheaper...

- Andy


I think the force holding the bowl onto the drum chuck or faceplate is
approximated by 0.5Xvacuum in inches of mercuryXarea of workpiece under
vacuum. For large diameter pieces this can be a very large number and can
implode/crack the workpiece if it is thin. If the diameter of the bowl is
around 6" or larger under a good vacuum you can do a lot more than just
light touchup cuts.
billh