Re: To tool change, or not tool change

Ballendo,

SCMI CNC routers have a neat way to get around the need for spindle
orientation. The holders and the spindle nose both have face gears
that loosely mesh as the toolholder is pulled up into the spindle.
The gear teeth are pointed so they'll mesh no matter how they're
oriented. This method would be easy to retrofit onto almost any
machine.

As to having machines that'll automatically "switch" tools, I've seen
a couple of clever ideas. The easiset to implement on a home-built
was a design on a gantry type wood router. They used multiple Z-axis
slides, each having it's own spindle motor with a different tool in
each spindle. Simply activate a different Z-axis slide when changing
to another tool.

Another idea on a wood router was to mount a number of air tools on a
six-position rotary table which was mounted in the normal spindle
location. The air tools were fixtured such that they pointed
radially out from the rotary table. The rotary table was attached to
the Z slide so the current tool was aimed vertically downward. At
tool change command, the rotary table indexed, bringing the next tool
into position. Very much like old Burgmaster drilling machines.

I agree about the ratcheting type automatic drawbars. Hate 'em!!


FWIW, even on high dollar production CNC's the toolchanger is one of
the biggest headaches. Have you seen any successfully operating home
built changers?

thanks,

Doug

--- In CAD_CAM_EDM_DRO@y..., "ballendo" <ballendo@y...> wrote:
> Doug,
>
> This was what Roland and I discussed...
>
> There are a few ways to orient the spindle: A shot-pin tied to rpm;
> i.e.,doesn't shoot-out until rpm is nearly zero. Adding a slow-
speed
> motor and sensor used like a car starter motor (stays out of the
way
> until a spindle orient is needed, at which point it "takes over"
til
> the sensor is read). sensor could be anything from a magnet/hall-
> effect to a "real" encoder index pulse. And the one Roland
> mentioned, "turn the HOLDER!, rather than the spindle".
>
> Those who have used these "ratchet wrench" draw bars either
love 'em
> or hate 'em, IME. Screwed up threads on holders and drawbar; did it
> or didn't it "take" seem to be the main reasons I've heard).
>
> This becomes more of a problem in something expected to run
> unattended; i.e., fully automatic.
>
> Hope this helps.
>
> Ballendo
>
>
> --- In CAD_CAM_EDM_DRO@y..., "doug98105" <dougrasmussen@c...> wrote:
> > Rab,
> >
> > There's a fairly easy way to implement an automated tool change
on
> > small mills. That is, provided the mill has some sort of draw
bar
> > pulling the toolholder/collet up into the spindle.
> >
> > Fit the mill with a Kurt type pneumatic draw bar assembly. These
> are
> > not much more than an inexpensive air rachet wrench. Chances are
> > you'd have to fabricate this yourself, I doubt Kurt & others make
> > these for the small mills. You'd need a spare M-code to activate
> the
> > pneumatics.
> >
> > Fabricate a rack, mount on the back or end of your mill table to
> hold
> > a few toolholders (note, this rack will use up some of your
> machine's
> > travel). To retrieve a tool move into position so the empty
> spindle
> > is over the tool, bring the spindle down over the tool and
activate
> > the power draw bar. The tool will be pulled up into the spindle
> and
> > locked.
> >
> > To change that tool, position back over the empty tool rack
> position
> > and drop the tool out by activating the power draw bar in
reverse.
> > Then move over to the next tool and repeat the above change
> procedure.
> >
> > If your mill has a key (like R8) or locating tabs (like 40 taper)
> in
> > the spindle those would have to be removed since you have no way
to
> > orient the spindle to align with toolholder.
> >
> > This isn't the most elegant tool changer, but it's far less
> > complicated than those used on high production machines.
> >
> > Doug
> >