by Kevin Burton
1.Reduce the feed
when you’re approaching the centre When you get to 2 mm (0.080 in.) from centre, begin backing off the feed by as much as 75 per cent. As you get towards the centre, the diameter shrinks, and the machine has to increase the rpms to compensate. But the machine can only compensate so much, and eventually, the rpms will drop.
2.Cease coolant flow when rpms decrease
Coolant helps with chip control, but through-coolant design may actually do its job too well in some cases when near the center. If the coolant is keeping the temperature at the cutting surface too low, it will create a built up edge that will shorten insert life.
3. Keep centre height within reason
Don’t get outside of ± 0.102 mm (0.004 in.) from centre height or you risk anything from chatter to total insert failure. When your setup is either too far above or too far below center, you’re likely losing valuable insert life.
4.Keep overhangs short
The usual rule of thumb is to not go more than 8-10 x the insert width. But if you can, keep overhangs short to make sure you’re always cutting with good rigidity and good security.
5.Stop feed just before centre
Stop feed completely just before you hit zero point and let gravity and component weight do the work. If you feed the cutting tool straight to the centre, or even worse, through the centre, you’re exposing the tool to less than ideal conditions—rpms, for instance, are zero at centre. The insert can be hit by the part falling off, causing edge damage. Or, if there’s a sub spindle, an operator can twist it off the part and pull it away from the feed bar.
Kevin Burton, product specialist, Sandvik Coromant, Mississauga, ON