Nice work, but I'm lazy and pragmatic. I just bought mine. That Dayton motor you used is probably worth more than my Frankford Arsenal tumbler. Surely a better motor too.
Thanks for sharing, I admire your ingenuity. The whole key is to match the motor and suspesion springs that don't hit a resonant freqency while you have the motor running.
You can adjust the force imparted to the device by increasing or decreasing the distance away from the motor shaft and/or the mass of the offset weight.
Sometimes, when I overload my Frankford Arsenal tumbler, it'll find a resonant frequency and kinda hop it up and down and polish poorly. Keep an eye out for that.
To assist any of you interested in engineering the force imparted into your device, use this equation.
Fn=mv^2/r
Fn = normal force, radial in this case
m - mass of offset weight
v - tangential instantaneous linear velocity of the offset mass. (V= r*omega) (omega is the rotation in radians per second, which is 2*pi*rpm)
r - radius of mass away from center of rotation.
I always use metric units, then convert, simpler math.
What this amounts to is simply increasing or decreasing the offset weight and it's distance until it works sufficiently. Adjusting the offset mass will not change the harmonics of springs, they may match or resonate the frequecy of your motor, which is revs per second in this case. 5000rev/min*1min/60secs = 83.3 revs/second However, overloading your tumbler might slow it down enough to do so as is the case in my storebought tumbler. If you devise your offset mass similar to the third picture, with a bolt that's threaded all the way to the bolt head, you can make it adjustable. You grind a flat spot in it at the threads portion right up against the bolt head or close to it to drill your through hole. Then drill and tap your retaining lock bolt or set screw through the head of the bolt. Now you have a portion of threaded bolt that you can screw a nylock nut on and have an adjustable tumbler.
Once you find your sweetspot, you'll probably never adjust it again, but since this is DIY and all, I thought I'd put some math behind it. If you made it this far, I'm surprised and thank you for letting me get my geek on.