Baz,
I have had that problem on occasion. I can't tell you what causes it but I discovered that right before it happens I can hear the air assist stay on. If I hit the reset button (Epilog 24TT) before I engrave the next piece it will engrave fine. Just something to listen for.
Mikey
www.pictureitinstone.com
www.jadeputters.com
"Both optimists and pessimists contribute to the society. The optimist invents the aeroplane, the pessimist the parachute."--- George Bernard Shaw |