Re: [CAD_CAM_EDM_DRO] ...but how much precision????

Bill Kichman wrote:

>Thanks for sharing your experiences guys...what I was basically after, is,
>how precise must my machine's backlash be, to attain a reasonable amount of
>precision, all other things being equal, without having to resort to
>ballscrew conversion. And additionally, how much precision is typically
>merited in machining work As I understand it now, most professional cnc
>machines are lucky to attain 0.0005 to .0015 accuracy. Sound correct?
>I spent a part of last evening adjusting the acme screws on the old 1945 Van
>Norman mill that I will be converting to cnc, and using a dial indicator,
>was able to reduce the backlash on all 3 axes to within (1) thou. The
>handwheels are a bit tighter than I would want for manual use now, but I
>don't intend to do a LOT of hand turning :-) This machine is in great
>shape, they don't make things like they used to.
>
>

That is VERY good on a used machine. Usually, the center of the screws
are worn more
than the ends, and if you tighten the nut so it just binds a little at
the ends, you still have
a lot of backlash at the ends. On my old Bridgeport, I tightened up the
nuts, and got
about .015 in the middle of the X, and about .025" on the Y, which I
knew was
BADLY worn. .001" blacklash measured at the table is very good, and
will
make CNC work well. You still have the higher friction of Acme screws,
though,
but a stronger motor can overcome that.

Jon