Re: [CAD_CAM_EDM_DRO] Air spindles

Ian Wright wrote:

> Hi,
>
> I'm trying to understand how air spindles work and decide how practical it
> might be for me to make a small one for some miniature engraving work I need
> to do. Does anyone have any links to sites with cutaway drawings of these
> beasts or perhaps a dismantled one on the bench which they could post a
> photo of somewhere? Thanks,

A photo of the inside of a Westwind spindle would not give you much
info. It looks like a solid bar with a flange on the end that fits into a
heavy tube about 1/2" ID and 1.5" OD. Of course, if you can look
more closely, you see more detail. There is a centrifugal collet chuck
on one end of the spindle. I have never taken this apart, but can make some
guess about the mechanism. I can imagine a bunch of collet segments
with a hinge point, and a weight above the hinge. When spinning, the
centrifugal force outward on the weights causes the collet segments
to grip the tool tightly.

The middle of the spindle contains tiny motor rotor laminations, just like
a miniaturized AC induction motor, as that is what it is.

The middle of the stationary part also contains motor stator laminations,
wound with 3-phase windings. I don't have the foggiest idea how they
get the windings up through the bore and packed into the tiny slots
in the stator core.

The outer part of the air bearings are bronze slugs, with the id precisely
machined, and tiny (about .015" or roughly 1/4 mm) holes around the
periphery where the air comes in. The inner part of the bearing are
finely machined stainless steel, with about .0005" of clearance, I think.
The thrust bearing is a big SS flange on the back of the spindle, about
1" diameter. The stationary part consists of two bronze plates (one is
part of the upper radial bearing) separated by a lapped spacer ring.
Both of these have about 10 holes in a ring for the air inlet. Air for the
back side thrust bearing comes through that lapped spacer.

The spindle is balanced phenomenally well, of course, so you can actually
not sense the thing is spinning when you hold it in your hand! (If you
twist it orthogonal to the rotation axis, however, the gyro moment
makes it quite clear it IS spinning!)

Jon