Re: Manual to CNC Lathe Conversion -THREADING

> This would be based on final part accuacy, no ?
>
> I mean that if there was a slow, the software would try to catch up
> and be either dead on the next pulse, or too short or too far.
>
> Assuming it was dead on, that would mean that at least on thread was

off.

>
> It would go back to the old saying, accracy costs money, how accurate
> can you afford to be ?

On commercial threading a quadrature encoder is used to assure
accurate threads at any speed up to the limit of the Z axis motor.
Thread pitch variation better than the lathe, lead screw accuracy is
possible( likely on a hobby machine ).

On just about any lathe, there is a combination of parameters and
cutting conditions (number of starts, thread pitch, material, tool
condition, etc) which will cause a spindle to slow too much for an
accurately cut thread.

Interchangable parts are possible in large part due to the creation of
standard shaped and sized (and toleranced)screw threads. While a make
to fit thread may be OK for a one-off, it is very unlikely that an off
the shelf nut will consistently fit the turned screw. Fit means not
too loose as well as not too tight.

> I think in practice, this is more of a problem in rough cuts and
> finish cuts should not see deviations is alignment.

The single point threading process is a series of finish passes,
followed by a single burnish/rub literally "for good measure".

DeskCNC uses a quadrature encoder to assure that the threading tool
position is located at the correct posiiton at all a times during the
cut.

This is especially critical on small machines which have both lightly
powered spindles and axis drives ( the definition of a hobby machine?)

Here is a white paper I wrote on single point threading:

http://www.imsrv.com/deskcnc/lathe/desktopcncthreading.pdf

Some threading pictures here:
http://www.imsrv.com/discus/messages/1004/101600.html

Fred Smith - IMService
http://www.cadcamcadcam.com/hobby