On the Super 7 I always understood that one didn't use back gear in high speed

Roy

Correct. Back gear, low gear, speed from about 26 to 158rpm.

JA

John

I don't know if this will be of any use to you but I have checked out my lathe. It is quite a bit different from yours in as much that it has an inverter, single pulley drive to the countershaft and two pulley drive to the spindle. The ratios from the countershaft to the spindle are about 3/5 and 5/3.

When the lathe is run in low gear, without back gear engaged, there is slight vibration above about 660rpm which increases with speed but is not bad up to the maximum speed of 1050rpm. In high gear, without back gear engaged, vibration starts at about 2000rpm. Again it is not bad.

This suggests that the vibration comes from the countershaft/clutch and starts at about 1100rpm. The spindle, as one would expect, appears to be vibration free.

I hope this is of use.

JA