Re: [CAD_CAM_EDM_DRO] Climb milling was feeds and speeds.

Woody wrote:

> Jon Elson Wrote:
>
> >
> > You can't climb mill safely on machines with sloppy leadscrews.
> >
> OK. This is something I was taught in High School (ok I was taught
> NEVER to climb mill)
> But nobody ever told me WHY. I THINK I can understand the change in
> forces in the system but not exactly how they relate to a sloppy leadscrew
> and why a tight ballscrew is OK.

The rotation of the milling cutter will draw the work into the tool. If the
leadscrew is tight, and there is a hand on the handle (or a CNC control)
to keep it from accelerating into the cutter, then things are OK. With (manual)
ballscrews you must not take your hands off the handles, because the ballscrew
is not self-locking, as the 5 TPI Acme screw is, and it will offer no resistance
to the work leaping into the cutter.

Even with a CNC machine with sloppy screws can't be trusted to climb mill
safely. Either manual or CNC, if there is more backlash in the screw than an
acceptable chip load (feed per tooth) then the work can jump into the cutter
with disasterous results, such as the cutter exploding, the work being ripped
out of the vise, the machine knocked out of alignment, spindle stalling, or
all of the above at once (which I have seen myself!)

With small backlash, even if the work jumps into the tool by the amount of that
backlash, it might only cause a small surface finish change, as long as the
backlash is less than an amount which the cutter can safely handle on one
cutting tooth. That could be .010" or more for a 1/2" end mill on a Bridgeport,
to .001" on a 1/16" end mill on a Sherline. (On the smallest end mills, the
cutting forces are not enough to pull the table against friction, so they are
rarely a problem.)

I always climb mill a finish pass, at least, even with a manual machine, because
the surface finish is much better. You have to be aware of what cuts will
produce enough force on the table to possibly overcome friction.
Now that I have a pretty tight CNC machine, I do almost all work in
the climb direction.

Jon