Re: noob laser question

Hi,

this is one of my questions - and this is why I kept posting the
method I intend to use for balancing. I feared the spring will somehow
"oscillate" and the cutting tool won't get the heavy little part that
needs to be removed. I was thinking about doing this little by little,
very slowly increasing the rpm. But I guess it won't work.
So I will have to mount an accelerometer and an optical sensor to
identify the heavy spot and then try to remove it with a micro drill
or smth.
BTW, has anyone here done that before? Any draw or smth for this kind
of device?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@...> wrote:
>
> 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
>