Re: CNC lathe question

Keith:

To cut threads in a metal lathe, a set of gears synchronizes the
spindle with the carriage. A normal wood lathe of course lacks these
gears. For that reason people sometimes use a metal lathe to cut wood.
A router is easily accomodated on top of the carriage. I would venture
to say that you can get a metal lathe for less than a good CNC
conversion of a wood lathe, if all you want to cut is flutes and
spirals.

Expensive CNC turning centers often have what is called "controllable
spindles" usually powered by servo motors. A servo motor is just a
motor that sends feedback to the controller while the controller
adjusts the speed. They are able to cut threads without the gears,
since the controller is the equivalent of an electronic set of gears.

In addition, most wood lathe's slowest speed might be too fast for
routing spirals and flutes. The spindle speed still needs to be
synchronized with the cutter. An encoder (like a tachometer) can be
added to the lathe head. Now you need a CNC controller that takes
feedback from the encoder, etc.

Thinking about this (for the last few months, no less !!) I have come
to the conclusion that there are a two good ways to accomplish this.

One, and probably the least expensive one, would be to add an auxiliary
motor to the spindle. The lathe head then would function just like a
rotary table (4th axis), and any CNC software capable of controlling a
4th axis should work with it. The motor can drive the spindle by means
of timing belts and pulleys, which can be on the outboard side. These
have little notches in them that mate to keep the timing accurate; they
don't slip.

The second, best but most expensive, is to use a cnc mill with rotary
table 4th axis.

I sometimes wonder why the Legacy mill does not have a driving
motor ....

Hope this helps, best regards !

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Keith Clark" <mail@t...> wrote:
> I am trying to build a CNC controlled router to mount onto a
> woodturning lathe. It will hopefully do shaping but I am also hoping
> for thread operations for barley twists etc. Does it seem reasonable
> to have 2 motors, one variable speed spindle motor for normal lathe
> operations and another stepper motor to do the threading operations?
> Would it be possible to do threading with the variable speed
> controller
> and spindle motor alone. It seems this would require a very accurate
> knowledge of the RPMs to time the travel of the carriage. I am
> thinking that a stepper motor would be accurate enough, but probably
> not turn fast enough for normal lathe operations.
>
> I know how it works on my manual metalworking lathe, but I will not
> have the gearing that lathe uses.
>
> Thanks for your input,
>
> Keith Clark