Re: [CAD_CAM_EDM_DRO] Re: Lathe CNC retrofit

Hi John:
That's a great idea!!!
I have only one question with a ballscrew in this application.
I was under the impression that with a ballscrew, you can sometimes spin the
screw by putting pressure on the carriage or the cross slide.(kind of like
the knee that drops when you disconnect the Z axis servo)
Were you going to use the inertia of the motor to help overcome this?
Or maybe drop a friction pad onto the screw during hand motion?
It would be a real pain to have to keep a hand on the crossfeed screw to
keep it from unwinding during a cut, or have the carriage backing up on you
everytime you tried to face off a plate.
Cheers

Marcus

----- Original Message -----
From: "stevenson_engineers" <machines@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Wednesday, January 30, 2002 4:13 PM
Subject: [CAD_CAM_EDM_DRO] 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.