Re: CNC lathe question

Victor,

Thanks for your input. I think I am on the right track then. I
will use the existing motor for rapid rpm work and add a stepper
motor to control the 4th axis for threading. It is already set up
for very slow rpm through the timing pulleys and with a tachometer
to calibrate it, It might be possible to run it as is with CNC
control of the carriage. This lathe is a gigantic one so
replacement with a metal lathe is not an option due to the cost.
Should be fun to work out the problems. I appreciate your
thoughts. I too wonder why the Legacy still is without motor...

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "victorlorenzo"
<victorlorenzo@y...> wrote:

> 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 !
>
>
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>
>
> --- 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