Date: Fri, 03 Nov 2000 16:57:20 -0700

Author: Jim Krider

Subject: RE: Measuring Ball Bearings

Post:

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Many years ago I worked as a precision tool grinder. We had a projection
device for measuring curvature that would cast a silhouette on a screen.
Unfortunately, for this discussion, we did not make balls. We did, however
measure radiuses on countersinks.

A circle was drawn on tracing paper and taped to the screen. The silhouette
could be seen through the tracing paper and was compared to the circle.

For a sphere a similar test could be made to cast a silhouette on the screen
with a device to hold and spin the sphere. You then spin the sphere back
and forth slowly comparing it to a circle.

We had a precision cylinder exactly one inch long with which to calibrate
the silhouette.

Perhaps something like this could be made to measure your ball bearings.

Jim
******************************************
Jim Krider James.Krider@asu.edu
Physics and Astronomy Instructional Resource Team
Arizona State University Department of Physics and Astronomy
PO Box 871504, Bldg. PS Rm. F470,Tempe, Arizona 85287-1504
Phone: 480-965-8086 FAX: 480-965-7954 Web:
http://www.public.asu.edu/~jkrider/



-----Original Message-----
From: Paul O. Johnson [mailto:pojhome@swbell.net]
Sent: Thursday, November 02, 2000 4:36 PM
To: Tap-L
Subject: Measuring Ball Bearings


I have a team of undergraduate students who plan to enter a NASA contest to
conduct a physics experiment in low to zero g aboard an airplane near the
top of a big outside loop. The experiment they want to do is to investigate
how the value of g affects the traditional method of making ball bearings --
putting drops of molten metal in free fall while they freeze.

They imagine the liquid drops will assume a spherical shape due to surface
tension, but air drag will distort the sphere a tad toward a teardrop shape
while the drops fall. If the drops fall slower at smaller values of g, they
should suffer less distortion and should freeze in a more spherical shape.

Their main question is: how can they measure the roundness of the frozen
balls? How do bearing manufacturers do it?

Any ball experts out there?

Paul O. Johnson
Collin County College

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charset=3Diso-8859-1">
5.5.2652.35">
RE: Measuring Ball Bearings



Many years ago I worked as a precision tool =
grinder.  We had a projection device for measuring curvature that =
would cast a silhouette on a screen.  Unfortunately, for this =
discussion, we did not make balls.  We did, however measure =
radiuses on countersinks. 



A circle was drawn on tracing paper and taped to the =
screen.  The silhouette could be seen through the tracing paper =
and was compared to the circle.



For a sphere a similar test could be made to cast a =
silhouette on the screen with a device to hold and spin the =
sphere.  You then spin the sphere back and forth slowly comparing =
it to a circle.



We had a precision cylinder exactly one inch long =
with which to calibrate the silhouette.



Perhaps something like this could be made to measure =
your ball bearings. 



Jim

******************************************

Jim =
Krider           =
            =
     James.Krider@asu.edu


Physics and Astronomy Instructional Resource Team =


Arizona State University Department of Physics and =
Astronomy


PO Box 871504, Bldg. PS Rm. F470,Tempe, Arizona =
85287-1504


Phone: 480-965-8086   FAX: =
480-965-7954   Web: HREF=3D"http://www.public.asu.edu/~jkrider/" =
TARGET=3D"_blank">http://www.public.asu.edu/~jkrider/







-----Original Message-----

From: Paul O. Johnson [ HREF=3D"mailto:pojhome@swbell.net">mailto:pojhome@swbell.net]=


Sent: Thursday, November 02, 2000 4:36 PM

To: Tap-L

Subject: Measuring Ball Bearings





I have a team of undergraduate students who plan to =
enter a NASA contest to


conduct a physics experiment in low to zero g aboard =
an airplane near the


top of a big outside loop. The experiment they want =
to do is to investigate


how the value of g affects the traditional method of =
making ball bearings --


putting drops of molten metal in free fall while =
they freeze.



They imagine the liquid drops will assume a spherical =
shape due to surface


tension, but air drag will distort the sphere a tad =
toward a teardrop shape


while the drops fall. If the drops fall slower at =
smaller values of g, they


should suffer less distortion and should freeze in a =
more spherical shape.



Their main question is: how can they measure the =
roundness of the frozen


balls? How do bearing manufacturers do it?



Any ball experts out there?



Paul O. Johnson

Collin County College




=

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