Re: [CAD_CAM_EDM_DRO] Re: noob laser question

Cristi wrote:

> Hi,
>
> Just need to remove very small ( tenths of miligram ) pieces from that
> disc. The disc is about 50 mm diameter and about 30 grams weight or
> smth like this.
> I really need to balance them as I intend to use them in an inertial
> platform, so I would like to remove vibrations as much as possible. I
> know I can add low-pass filters to the accelerometers for vibrations,
> but I prefer not. I would like to know if I can balance it using a
> lathe cut tool so I can avoid the laser.
> Balance is done holding the disc with a ball bearing suspended with 3
> springs, in perpendicular plane to the axis of rotation.

Inertal measuring unit stable platform? Ohhhh, man!

I would suggest using a "strapdown" scheme, and use either the
"wine-glass" rate gyros from Kyocera for low-resolution work, or
a fiber optic interferometer angular rate sensor. These are
actually available off the shelf for reasonable prices, but you
could do your own without great effort. (They use a special
low-grade laser called a Super-Luminesecent Diode to avoid mode
locking with the fiber spool.)

I gather you thought you could balance the rotor by just shining
a CW laser at the edge while it spun, or now just touch the edge
with a cutting tool. That will make it ROUND, but it won't
balance it. If you mount it on springs, it will vibrate,
especially if you apply a cutting tool to the edge, it will
bounce off. You will end up with a non-round rotor which will
actually be WORSE than it was before. The laser at least
wouldn't cause the bouncing, but if I remember how this all
works, the unbalanced mass causes an acceleration, so that the
peak deflection of the axis occurs 90 degrees behind the heavy
spot. So, the laser would burn off material trailing the heavy
spot by 90 degrees of rotation, never actually fixing the imbalance.
You have to deal with tiny density variations in the material as
well as tiny manufacturing variations. There is no alternative
to determining where the heavy spot is and then removing in
by specific effort. A computer could do this by measuring the
location of the heavy spot and then timing a laser to fire at
the right time to burn it off. A CW laser (if my physical
understanding of the problem is right) will never work.

If you only need to remove tenths of a mg, then just determine
the heavy spot and rub it on a piece of paper a couple times.

Oh, what are you making your 30,000 RPM rotors out of? Better
not be aluminum, or we'll be reading your obit soon. (We had an
aircraft instrument tech killed here about a decade ago when he
hooked a 12 V aircraft gyro to 24 V by mistake, and the rotor
exploded and killed him.)

Jon