I've been using a cheap $20 jigsaw to shake the bejeezus out of my paints for a while, and it works very well.
Up until now, I've just been clamping the paint bottle to the masking-tape wrapped blade of the jigsaw with a bulldog clip, and that has worked OK, but from time to time I do get a flying paint bottle. Also, it's a bit of a faff getting everything mounted properly.
So, I've made this modification.
The main body of the frame is just a bit of plywood that I've cut out, drilled, and epoxied to the jigsaw blade. I filed down the teeth of the blade for safety's sake. The bottles are held in place by some bits of velcro I had left over from some household job or other; they're just stapled to the plywood frame.
I can shake two bottles at a time with this setup, though how the jigsaw will cope with all the extra weight and vibration in the long term I don't know. It cost very little though, so I'm not risking much.
I cut a notch in the cap end of the frame to give the bottle some lateral stability. I don't know how necessary that is, but it can't do any harm.
