my dilemna is that one of the barrels bursts open - on average -
once an hour.
Catherine, I have that problem with my Lortone 45C and got some good
advice from the Tech. Dept. at Rio, which I incorporated into my
article on tumble-polishing metal jewelry, published in Lapidary
Journal, July 1999, pp. 75-77. Assuming you may not have that on
hand, here's what I do.
First, I set up my whole assembly on wood blocks (about half an inch
thick), inside an old, large aluminum cake-pan, so that the mess
produced when the cover spontaneously comes off, stays inside the
pan. The blocks keep liquid from getting into the motor.
Also, (this was the advice from Rio), I take a short, thick, blunt
piece of wood and place it under the center of the barrel after it
is loaded, then gently push the barrel downward so that its
bottom is slightly arched up upward. Holding the barrel in this
position, put on the flat inner lid and the upper metal lid, then
tighten the knurled knob. The bottom should remain slightly
indented, and the positive air pressure outside the barrel will
help keep the lid in place.
It's not 100% foolproof for me, because I tumble heavier things,
but it may be fine for you.
HTH (hope this helps)