OK, you might be mixing apples and oranges here.
A vibratory tumbler for large steel objects will clean up the surface, remove discoloration and scale, and leave a nice matte finish. It won't be suitable for leaving a fine finish above 400 grit. That works to some degree on small parts with plastic media and grit/polish, but not well on parts like knife blades. Walnut and rouge will also produce a polish, but aren't going to work as well on blades. You can experiment, but remember that you will need to empty the tank and change the media it with the next step to go up the grits. Media runs from $2 to $5 per pound, and a large tumbler will hold 25-100 pounds. This can get expensive with a set of four to five steps costing about $1000. It is reusable for a long time, but careful cleanliness will be necessary to avoid grit contamination.
A smaller vibratory polishing table or bowl will work so-so on knife blades. I have given away several 20 pound units, and as far as I know no one kept on using them for tumbling blades. The only folks I know who use this type on blades are folder makers.
Use either ceramic media and loose grit or use impregnated plastic media. Pyramids work best for larger pieces. I know that Daniel Boone VII in central VA uses a huge tumbler to finish his decorative blacksmith pieces. His tumbler is a 4' tank model that holds about 100 gallons ( or more?) of dry media. It makes a lot of noise. Nice guy...give him a call - 540-967-3267 .
I just purchased a vibration motor for making a smaller unit with a 18-24" tank and will build it with the new shop. It will be outside, and must be mounted on really solid support posts cemented in the ground. It will have a cover for when not in use. Being outside will allow easy wash out of grit and swarf. My plan is to make an elliptical segment tank and mount the vibration motor on one side near the bottom. I will experiment with a plywood mock-up to get the placement and orientation of the motor right before making a 16 gauge steel tank and installing a rubber liner.
The motor has 100Kg of vibration force, so it should shake the tank nicely, setting up a rotation. It is 3Ph, so I can increase and decrease the speed to tailor the finishing. A timer and the speed control will run it.
