Quoting from "Moltrecht":

"When cutting a thread with a split nut continuously engaged, the spindle
speed must be slow enough to allow the operator to have complete control
over all of the lathe movements at all times. Thus, the spindle speed used
depends upon the judgment of the operator. He should consider his
experience in cutting metric threads on inch lead-screw machines, his
experience on a particular machine, the ease with which a particular machine
can be manipulated, and the size and type of thread being cut. All other
machine settings made in preparation for cutting threads are the same as
before, except that the 127-tooth translating gear must be used in the gear
train."

One good way to maintain necessary control is to rotate the spindle
manually. I do this with a crank on the outboard end of the spindle.
Another way would be to turn off power to the spindle with enough room left
for it to coast to a stop. Then when almost stopped continue to turn the
chuck by hand. The moral to this is - metric threads aren't as easy to cut
on "English" machines as English threads are. Leave the gears disengaged
from the motor when turning the spindle by hand. Cranking back by hand is a
lot easier to do if you aren't dragging the motor along.

Bob Swinney
wrote in message
oups.com...
This lathe is advertised as being able to cut english and metric
threads. I have had no problems making english threads.

According to the manual, in order to do metric threads you must do the
following:

Change gears - i.e. for a 1.5mm thread, select the two 48 teeth gears
and run one on the 120 main gear and run the lower on the 127 gear
(machine has 120/127 double main gear for converting to metric).

Select the proper combination of levers - i.e L,T,A,C according to the
chart printed on the front of the lathe.

Disengage feed selector to the "O" posotion.

Now, when cutting english you use the dial indicator and
engage/disengage the half-nut lever. On metric, the manual says to
engage the half-nut lever and leave it engaged during the whole process
of cutting the thread.

However, the manual fails to tell you how to stop the machine at the
end of the cut so that you can reset the depth on the cross-feed. You
cannot reverse the direction of lead screw travel as suggested by an
authorized jet technician for three reasons. One, there's a large
warning on the front of the machine telling you not to do this. Two,
it doesn't work since you are temporarily changing gear teeth when
moving the selector know, therefore you are off when reversing and
coming back into the cut. Third, changing the lead screw direction
goes from cutting right-handed to left-handed threads when changing
directions.

It seems that the procedure involves leaving all gears continually
engaged. Then you cut the forward/reverse lever on the apron section
to the neutral position to cut power to the travel. The head continues
to rotate due to momentum until it comes to a rest and the magnetic
latches release on the motor. Then you back out the cross feed, jog
the machine backwards using the jog button, reset your depth and do
another cut. This appears to work, but what do you do to stop the
drift after stopping? If you need to thread a half inch piece that has
a 1/4" relief and then projects into a 60 degree bevel towards the
chuck, you risk crashing the tool into the part when trying to guess
where the momentum will stop the carriage. This machine does not come
with a brake and jogging the machine backwards immediately after
disengaging the feed start lever does not work since the motor does not
disengage the latches until it comes to a complete stop.

I have read other scenarios about reversing with other machines, but
this is designed to run 220V single phase. Any help would be
appreciated.

DC