"I've tried dry tumbling endlessly. The material warps, due to the heat from the friction of the grit."
Nature has a way of creating materials with mechanical properties that can not be reproduced by man.
Clay and cane sugar are two such materials. Apparently tortoise shell and probably bone.
Due to the sensitive nature of your target to water and probably other fluids it would seem that dry tumbling is your best avenue. A meat cooler at the average grocery store is kept at 35F. The cutting room at 38 to 40F. There should be no problem dry tumbling at 35F to 40F ambient.
Or perhaps a fan could keep the batch cool.
Is the vibe motor close enough to the hopper to cause heat to transfer to the hopper ?
Heat born from friction in a vibe is real. No doubt about that. Let's cool the process !
The rocks in my Vibrasonic tumbler get so hot during my Georgia summers that they are unbearable to touch.
This vibe has poor air flow and a big 1/3 hp motor turning at 3450 rpm somewhat enclosed and mounted directly under the hopper.
Lot's of heat generated...
However the rocks run cold in the Vibrasonic when outdoor temps drop to winter levels.
Not exactly sure how cold the outdoor ambient temp must be, probably from 25F to 40F.
Cold enough that I must use less sugar for a slurry/lubricant since the viscosity increases rapidly as sugar syrup cools(think pancake syrup).
Oil has high heat capacity, consider the high amount of heat stored in cooking oil for instance.
And most fluids have a higher heat capacitance than dry conditions where gas/air is involved.
Sugar syrup certainly holds a lot of heat.
Thoughts for consideration...
Jim
B.S.M.E and more importantly P.H.D.I.H.O.E(PHD in hands on mechanical engineering he he)