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## ball mill question answered (long)

### wayneinkeywest on wed 17 dec 03

Many, many thanks to all who took time to write
regarding my interesting experiment in
creating a cheap (under \$100) ball mill.

The experiment was a qualified success:

A five gallon bucket with only one "vane"
made of 1x1 aluminium angle bracket attached
on the interior wall of the bucket was just enough
to tumble contents when loaded into
a regular gas (or electric) clothes dryer.

Plywood plates had to be installed to the outside
of the bucket with "L" brackets to stabilize it inside
the dryer drum, which rotates at a speed of 73 rpm
based on the following equation:
diameter of the motor pulley (1inch) divided by the
diameter of the drum pulley (24 inches) times the
rpm of the motor (1750) equals 73 rpm
expressed mathematically: (1/24)X1750=73

My sincere thanks to repairclinic.com for providing
me that formula.
Did you know that the rpm of a clothes dryer drum
is not listed on any manufacturers website, or
in any owners manual? Interesting.

I installed it only temporarily, using the plywood
stabilizers inside the drum, since my partner is still
screeching about using the dryer for something other
than clothing, and it all had to be removed
before a murder (mine) was committed.

Since the bucket has a diameter of 15 inches (which
yeilds a radius of 7.5, the square root of which is 2.738)
the formula for critical speed becomes:
29.923 divided by 2.738 equal 10.93
correct speed becomes (87+64%/2)=75.5%(average)
of 10.93, or roughly 8.27rpm. That's not gonna get it...

Working backward, since we know that the drum rotates
at 73 rpm (without modifying anything on the dryer):
73R=22.59
R=3.23
Isn't math fun?
Since I have no interest in a container having a diameter of
6-1/2 inches (too small)
I installed the aluminium vane (as a test. I'll make one from
porcelain soon enough) in the five gallon bucket, gave
it a half charge of water mixed
with sand and some local "pea rock" from the pathway,
installed it in the dryer (muttered a prayer) and turned it on.
(Make sure your container is water tight first...)
I now have a working ball mill, a pissed off partner, and a
neighbor that told me "to have the bearings checked on
that dryer, 'cuz it sounds like a broken stone crusher."

Can I consider that a compliment? :>)
Wayne Seidl

### pdp1@EARTHLINK.NET on thu 18 dec 03

Hi Wayne,

Too...since there would be some slip between the Drier's
rortating Drum's interior and the Bucket as roll against
it...

The actual speed at which the Bucket shall revolve will be a
matter of it's diameter against the internal diameter of the
Drier's Drum, minus the slip..

The drier's Drum likely runs from a Belt and Pulley
arrangement from an electric Motor, and, the ratio of the
Pulleys could be changed to effect a different Drum speed...

If all this had been said, forgive me for the redundance! -
I have missed some of this...

Best,

Phil
Las Vegas

----- Original Message -----
From: "wayneinkeywest"

> Many, many thanks to all who took time to write
> regarding my interesting experiment in
> creating a cheap (under \$100) ball mill.
>
> The experiment was a qualified success:
>
> A five gallon bucket with only one "vane"
> made of 1x1 aluminium angle bracket attached
> on the interior wall of the bucket was just enough
> to tumble contents when loaded into
> a regular gas (or electric) clothes dryer.
>
> Plywood plates had to be installed to the outside
> of the bucket with "L" brackets to stabilize it inside
> the dryer drum, which rotates at a speed of 73 rpm
> based on the following equation:
> diameter of the motor pulley (1inch) divided by the
> diameter of the drum pulley (24 inches) times the
> rpm of the motor (1750) equals 73 rpm
> expressed mathematically: (1/24)X1750=73
>
> My sincere thanks to repairclinic.com for providing
> me that formula.
> Did you know that the rpm of a clothes dryer drum
> is not listed on any manufacturers website, or
> in any owners manual? Interesting.
>
> I installed it only temporarily, using the plywood
> stabilizers inside the drum, since my partner is still
> screeching about using the dryer for something other
> than clothing, and it all had to be removed
> before a murder (mine) was committed.
>
> Since the bucket has a diameter of 15 inches (which
> yeilds a radius of 7.5, the square root of which is 2.738)
> the formula for critical speed becomes:
> 29.923 divided by 2.738 equal 10.93
> correct speed becomes (87+64%/2)=75.5%(average)
> of 10.93, or roughly 8.27rpm. That's not gonna get it...
>
> Working backward, since we know that the drum rotates
> at 73 rpm (without modifying anything on the dryer):
> 73R=22.59
> R=3.23
> Isn't math fun?
> Since I have no interest in a container having a diameter
of
> 6-1/2 inches (too small)
> I installed the aluminium vane (as a test. I'll make one
from
> porcelain soon enough) in the five gallon bucket, gave
> it a half charge of water mixed
> with sand and some local "pea rock" from the pathway,
> installed it in the dryer (muttered a prayer) and turned
it on.
> (Make sure your container is water tight first...)
> I now have a working ball mill, a pissed off partner, and
a
> neighbor that told me "to have the bearings checked on
> that dryer, 'cuz it sounds like a broken stone crusher."
>
> Can I consider that a compliment? :>)
> Wayne Seidl
>
>
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