Re: Ball screws

"F. de Beer" wrote:

> From: "F. de Beer" <f.debeer@...>
>
> List,
>
>
> Between Christmas and New year I bought a Bridgeport series I with a
> 2j2
> head. (I think the machine was made in the early seventies).I am now
> busy
> with retrofitting it with EMC to a cnc system. What very important is
> for me
> is that I can use the mill in both the conventional way and the cnc
> way.
> Here is my question: When I replace the original lead screws for ball
> screws
> I will loose the self braking behaviour if it ( don't know this is the
> right
> word for it) which I need when machining parts by hand.
> Any comments?

Yes, the self braking, or self holding feature of Acme screws will not
exist after
the ball screw modification. I would not be too worried about it, as
long as you
leave the axis locks operable. If you are milling, and need both axes
free, then
you must keep a hand on each handle all the time the cutter is in
contact with the
work. The real danger is when climb milling, which is a desirable
milling feed
to get optimum tool life and surface finish. The rotation of the tool
will tend to
pull the work into the tool, and that can cause a nasty crash. But, you
will find
you have excellent control over the machine, because there is no
backlash, and
you can feel the cutting forces more directly.

But, having made the conversion to ball screws and EMC, I have lost all
manual
operation of my mill, and rarely miss it. About the only time I find it
the
slightest bother is when I want to drill just one hole in something, and
it
takes a couple minutes to fire up the computer, start Xwindows, and EMC.

I don't have a drill press.

I find manual operation of the machine pretty easy, and like being
able to set up a move in MDI, and then concentrate on brushing
oil on and chips away, instead of turning handles. So, in a sense,
I haven't done any truly manual milling in about 2 years.

Jon