Re: Lathe CNC retrofit

>--- In CAD_CAM_EDM_DRO@y..., "Marcus & Eva" <implmex@a...> wrote:
> 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,
Hey man it was only a generic design. Do I have to build it for you?
[just joking <g> ]
Yes you are right though about them moving under their own inertia.
The greater the pitch the more this happens.
Because you want to use as a manual machine probably the best way
would be adjustable brakes on both handwheels so you can set preload.
I built a big grinder once that ground spherical ball valves over 64"
in diameter for the Russian oil fields. This had programmable infeed
on the carriage and air cylinders braked the cross slide when it
wasn't feeding. This would be hard to do on a lathe because you tend
to use both axis at the same time in manual mode.

John S.

>
> ----- Original Message -----
> From: "stevenson_engineers" <machines@n...>
> To: <CAD_CAM_EDM_DRO@y...>
> 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.