jamesp would that also be remediated by slowing the roll? It seems like if you are tumbling in a different shape (e.g. relatively narrow tire versus much wider barrel) you could trade off volume for speed, so the rocks roll over each other rather than bash each other.
In the link
hornseeker posted there is a video and the action seems at least potentially non-destructive (well no more than is helpful for rounding)
The problem I ran into was pretty simple. I was able to run the tumbler open to watch it like the above Youtube video John.
For a normal size car tire I was still getting a roll distance of 20-24 inches.
And the rocks rolled from top to bottom of that distance, some picking up what i consider too much speed.
Even if the tire rotated slow, a tilt was required to start the 'avalanche'. And the speed at the bottom of the avalanche was pretty fast.
A 6 or 8 inch barrel can rotate very fast but there is not so much high speed impact because the rocks are in a smaller container 3/4 full
and moving in a rolling blob, short 'avalanche' distance.
it is all about the avalanche within that caused my problems.
The big tire was really a failure because it had such a gradual slope due to it's large diameter. Causing the rocks to slip.
To avoid the slipping I had to increase it's speed, which powdered the edges and corners of the rock.
So I screwed kickers into the big tire to stop the slipping and slow it down and still had impact damage due toe the long avalanche effect.
The smaller the tire the less damage that occurred. But with a tire you are basically running a barrel 1/4 to 1/3 full.
By running a barrel at a normal 3/4 full the avalanche within is very short and there is no room for rolling speed to increase.
Just running a tumbler barrel at 1/3 to 1/2 full will impact frost without filler of thickeners.
So I never figured it out the tire tumbler. I have even canned my 8 and 10 inch barrels and run longer 6 inch barrels very fast.
They grumble instead of crash, and lots of grinding action seems to take place. Just a preference, not necessary,
and seem to coarse grind fastest.
Here are some photos that may illustrate. this is coral. It is virtually fracture free.
These are called crescent fractures from impacts
Notice the heavy frosting on the edges. Albeit, they rounded, but they are frosted and full of crescent fractures
This photo is of the same material done in a barrel. Granted it is smaller and less apt to bruise like big heavy rocks.
But it is a chip of off the same type coral above a shows how fracture free this material is
I went outside and cracked the round one in the above photo open. So the innards can be seen.
Then I remembered how I put so many special corals in the tire tumblers and beat them up.
The inside is pretty and fracture free.
and then the outside is a different story