On Wed, 15 Oct 2003 17:23:52 +0000 (UTC), (Dave Martindale) wrote:
Gary Coffman writes:

One thing you can do on even a $399 Harbor Freight lathe which you
can't do on a Taig or Sherline is cut single point threads. To do that,
the carriage has to be geared to the spindle so that the cutter's advance
is timed to the rotation of the work. This is done either via change gears
or a quick change gearbox (preferred) on most metal lathes.

Neither the Taig nor the Sherline are built that way. All cutter motions
are achieved by manually advancing handwheels. This also means it
is sometimes difficult to get a fine finish on the workpiece, ie because
you aren't as smoothly advancing the cutter as a lathe with power feeds
would.

That's true of the basic lathes as delivered. But Sherline sells a
threading attachment that drives the leadscrew from the spindle just
like any other change-gear lathe. (It is designed to have the work
turned by hand crank, not under motor power, which is a problem in some
cases). Sherline also has a power feed option that will give you
consistent finishes but won't do threading. Or you can get the
CNC-ready version of the lathe, put a stepper motor on the leadscrew,
and control it either with Sherline's CNC linear controller or a
computer and drive electronics. Again, this doesn't do threading, but
it does provide controllable carriage speed (and distance) - all using
Sherline accessories.

Then there is the Frog, for both Taig and Sherline. It's a stepper
motor plus electronic controller. It drives the carriage via the rack
on the Taig and the leadscrew on the Sherline. The Frog provides
variable speed/distance power feed like the Sherline indexer. It also
does threading, using a spindle rotation sensor to synchronize carriage
movement to spindle rotation.

I was going to mention all that, but decided not to. All of what you
say is true, but none of it applies to either basic machine as delivered,
and requires retrofitting by the owner. For someone just buying a first
lathe, I thought that was asking a bit much. OTOH, the HF minilathe
will cut threads right out of the box, and it works the way all the lathes
in the metalshop textbooks work, so the novice isn't confounded with
concepts that are a bit unorthodox.

Gary