Re: [CAD_CAM_EDM_DRO] Re: noob laser question

On Sat, 19 Jan 2008 12:44:12 -0600, you wrote:

>Sure. The traditional "electronic balancer" uses a dual-trace
>oscilloscope, a magnet moonted on each bearing and a coil of
>wire to pick up the motion of the magnets. It also has some
>optical system to shine a spot of light on the shaft and sense
>a black dot there as an index mark. This mark triggers the scope.
>
>You get the thing spinning, and raise the speed until the
>vibration becomes strong enough to make a clear wave on the
>scope. If both traces of the scope are roughly equal in
>magnitude and in phase, then you have a "static imbalance", ie.
>the unbalanced weight is roughly between the bearings. If the
>traces are in phase but one is much larger, then the excess
>weight is nearer on bearing. If they are out of phase, you
>have a dipole, with the weights on opposite sides rotationally.
>
>Depending on how the thing is set up, you have to learn how to
>interpret the scope traces as to where to remove metal. You do
>this with a Dremel or similar tool, and just grind off a little
>material at the periphery, then spin it again.

Exactly same way as modellers balance model turbine shafts, and they
turn at up to 200000 rpm.

The rig I made had two nylon yokes where the bearings sat, mounted on
flat spring steel uprights. Glued to the supports were small strain
gauges. They are cheap enough from a decent electronic supply house like
RS Components. (Not radio shack ;). Drive to get it spinning was a
simple model RC car DC motor, with flat pulley fitted and the drive belt
was simply a rubber band around the turbine shaft.

Balancing is done by adding tape until there is no oscillation on the
sensors readout, then removing the same weight in material from the
opposite side of the turbine wheel. A little bit of practice and it gets
very easy to balance out. We found that if it balanced at 10K rpm, it
would generally be fine up to 150k +

Metal removal was done with a Dremel initially, then a fine file.

Steve Blackmore
--