Re: Lathe CNC retrofit

The problem of driving a lathe via CNC and manual is easy to solve.
The CNC part is a standard setup. Ball screw driven by stepper or
servo driving a ball nut secured to the apron / carriage.
The manual part is handled by reverse engineering the feed from a
manual lathe.
Take a feed shaft from a manual lathe, you know the plain one with a
keyway down it. In this case though we just use a length of hex bar.
Position this to run under the ballscrew and be supported in
bearings / bushes either end. Behind the apron in a bushed bracket
free to rotate is the female of this hex part. This is the reason to
use a hex bar as it's off the shelf and you can use a six sided cut
down socket for the internal part. Saves cuting a long keyway in a
shaft and making an internal fixed keyed mating part.
Fastened onto the end of this socket is either a bevel gear or worm
gear depending on personal design or what's in the scrap box.
Driving this bevel or worm wheel is another bevel or worm with the
saddle traverse hand wheel on it. The reason for the gears is to get
the handwheel at 90 degrees to the feed shaft.
All that remains now to do is to connect the two up at the tail stock
end by gears or belts. If using worm gears a simple dog clutch is
needed to prevent the drive locking up in CNC mode. If using bevel
gears it can be left in mesh or just equipe the handwheel with a
folding handle so when it's in CNC mode there is nothing sticking out
to get caught up on.
In CNC mode the motor will drive the ballscrew and by default drive
the feed shaft and handle [ with bevels ]
In manual mode the handwheel drives the socket thru the gears and in
turn rotates the ballscrew and so moves the carriage.
Pay attention to which side you mount the bevels and the hand of the
ball screw so you get the turn the hand wheel the 'correct' way round.
I hope this description is claer enought. Depending on machine layout
you will have to fit to each machine. This is just a generic
description.

John S.