Todd Rearick wrote:
OK, so when one adds CNC to a mill or lathe, it's a good idea to upgrade to
ballscrews in order to eliminate backlash.....sounds reasonable to me, but
I'm a little confused about what this does for the leadscrew of a lathe. Is
there a special ballscrew that can be engaged/disengaged like a T-nut? I
can't quite figure out how anyone would thread with a lathe after replacing
the normal leadscrew with a ballscrew....seems like manual threading would
be completely out after that.

I suppose the CNC controller could perform the threading operation, but it
would need to know the spindle speed and phase...how is this normally done?

Todd


The only way to do it without CNC software that supports threading is to
have the ballnut be bolted to the carriage in an easily-disconnected
way. Unbolt to thread, put bolt back in for CNC.

CNC control that DOS do threading has an encoder on the spindle, and
"electronic gearing" that links the carriage motion to the spindle
rotation for a certain distance, then breaks back out of that mode
for the return pass. Note that almost all hobby-level programs do
NOT do electronic gearing. Every one I've seen does spindle
synchronization, then just does constant-rate motion for the thread.
This is just not as accurate as real gears or true electronic gearing,
where the spindle rotation rate is monitored all through the threading
pass. You can almost certainly tell that any program that uses a
one-pulse per rev spindle detector is doing sync, not electronic gearing.

Jon