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bjvoorRe: Small vibrating motor
Great ideas, thanks! Someone also suggested a motor - driving an eccentric on its own shaft (not as good) or a belt driven eccentric from a motorized "razor" child's scooter. The speed control from the scooter could vary the speed. Just steal it from your (or the neighbor's) kid.
BonaroRe: Small vibrating motor
Interesting thread.
I suppose the kind of vibration induced would depend on the goal. Do you want to settle the particles by mass or do you want to move the heavy particles in a particular direction.

The linear vibration would move the particles in a predictable direction but if you wanted to just settle then any frequency vibration if sufficiently strong will do that
overtheedgeRe: Small vibrating motor
If you have electricity at the site, you could use a vibratory sander for orbital vibration. This is what Karl von Mueller used in his vibratory concentrating table. I'm still seeking his book on the subject.

For linear vibration, consider a sabre saw or wait for it,
wait for it,
electric hedge clippers.

Have you ever taken apart a set of electric hair clippers? They have a most interesting reciprocal motor using a magnet as the rocking armature. They aren't so good for extended use; perhaps half an hour or so.

eric
FlengRe: Small vibrating motor
The ideal device for the job would be highly efficient and only induce enough vibration to get the job done and no more. Too much vibration wastes energy and will cause the table to destroy itself!

A very cheap vibration device is a relay rigged to oscillate like a buzzer. Depending upon the relay this might or might not be able to achieve enough deflection of the table surface to achieve the desired effect.

Another method would be to use a low frequency speaker attached to the table. One could tune the frequency to nearly match the mechanical system's resonant frequency and tweak the amplitude (voltage) of driving signal to save energy.

Here is a link to a cheap, efficient, low frequency driver:
http://www.mcmelectronics.com/product/MCM-AUDIO-SELECT-55-1250-/55-1250 70-100 Watt low frequency driver

For those that want to be sure there is enough "oomph" there is this $40 device:

600-1200 Watt low frequency driver

A simple tuneable power oscillator could be used to cheaply drive the speaker without a need for an amplifier or a signal source if anyone is interested.
MuleyRe: Small vibrating motor
Here is what I use, they great little vibrators adjustable speed and force.


Vibco SCR vibrators [115 clicks]

They are about the size of a peewee football and somewhat pricey,

Muley
BonaroRe: Small vibrating motor
Yep, you can design/build just about anything and with each improvement there is no doubt it will be better at doing whatever it does. The bell crank to create linear and not orbital vibration to better control the migration of the gold on the table is a good idea....but simplicity does breed endurance and the simple motor with out of balance pulley will probably survive for a decade of casual use before you have to change it with another thrift store motor.

It all depends on how you want to spend your time, fabricating a gold processor or actually processing the gold. :thinking:

I have spent huge amounts of time fabbing elaborate Rube Goldberg devices. They did work but at some point it became a project about the machine and not the gold so I tend to keep it simple now...whatever plugs your nozzle :clap:
overtheedgeRe: Small vibrating motor
A bell crank can be best visualized as a triangle with holes in each corner. One hole is the pivot (on an axle/stud) the other two are connected to rods/cables.

The whole purpose of a bell crank is to change the direction of motion. Example: "up and down" to "back and forth" sideways.

http://en.wikipedia.org/wiki/Bellcrank

In the case of the stamp mill drive, the rod that normally connects to the hammer shoe is connected to a bell crank instead. The bell crank can be either at the top or bottom of the rod.

Now the advantage as I see it.
The eccentric, that lifts the stamp mill rod, smoothly lifts the rod and then abruptly drops it. You could also add or substitute a spring for gravity to increase the cyclic rate. The gravitational constant (32ft/second ^2) limits the cyclic rate as stuff only falls so fast. The higher the cyclic rate, within limits, the greater the through-put for a given width.

It is easier and cheaper to construct a flat surface on a smaller table than a larger table. BUT!!!! The table doesn't have to be so perfectly flat to work just fine. The flatness is consumer driven, not function driven.

Consider beach deposits. The light stuff gets winnowed off by the waves leaving behind the heavies as lag. The beach isn't flat. Wave table?

But there are lots of ways to skin a catfish.
Try not to get tunnel vision when designing.
The trick is to keep your prototyping costs to a minimum because nothing works perfectly the first time. And try to have a bit of fun along the way.

eric
bjvoorRe: Small vibrating motor
Eric, I had the same feeling about a belt driven eccentric - good to hear someone else doesn't consider that folly. I'm not seeing the bell crank thing, though, and I'd like to! How about a description with a little more in detail for a "slow old guy"?
overtheedgeRe: Small vibrating motor
You will get a lot longer life out of your motors if you use a belt drive from the motor to drive the eccentric weight.

Many of these small motors use a bushing type bearings and direct drive puts high dynamic stress on the bearings.

You can then use different pulley sizes to alter the eccentric's rpm. Motors last longest when driven at their design rpm. Older sewing machine motor controllers were just variable resistors.

With small motors and their attendant size belt, you can make pulleys out of plastic, wood, whatever. Even jack-shaft and bearing can be scrounged and/or fabricated.

It usually doesn't cost hardly any more time and money to design and build the most efficient you can within your budget. And in the process, you gain proficiency as a fabricator. Almost anyone can insert tab "A" in slot "B". The skill was in designing the tab "A" to fit in the slot "B".

Anyway, one thing to keep in mind is momentum and the change in direction of said momentum. Newtonian physics can't be escaped.

Now just because I enjoy fun, I'll toss out an "outside the box" concept. Consider the power transfer mechanism of a stamp mill. Rather than a hammer and anvil at the bottom, substitute a bell-crank. Then a drive rod from bell-crank to table. Of course it would work just a easily with the bell-crank on the top of the stamp gang rod. This would put the drive mechanism lower than the table.

Of course, one could get really silly (or maybe not) and in keeping with the stamp mill drive concept, add more gangs driving more tables or perhaps a mix of stamps and tables.

eric
bjvoorRe: Small vibrating motor
Thank you for the comments!
Something there will work.
I like the idea of protecting the motor (whichever one I use) with an old plastic soda bottle - cut to fit over it. I'm constantly amazed at how creative you guys are.

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