(Copyright 2004 Allen’s Treasure House)
Tumblers must be operated with a full load. In rotary tumblers, that means 2/3 of the barrel filled with rocks, along with whatever abrasives and other ingredients may be required. You cannot tumble a single rock.
Rock tumbling proceeds in typically 4 stages, beginning with the coarse abrasive and then moving up sequentially to the medium, fine, and polish abrasives. Typically, between each stage, the rocks should be run through a brief cleaning cycle in a mild soap solution (consult machine manual for acceptable types of soaps). There are several different abrasives available for each of these stages but they are all used essentially the same way. One difference is that some polish agents do not require a final soap burnishing or cleaning cycle.
In a rotary tumbler, the required tumbling time is typically 1 week per stage, although this varies considerably depending on the rocks, especially in the coarse grind. Vibrating/sonic tumblers are considerably faster.
It is possible to get poor results from a tumbler when using good materials, by improper composition of the load. Probably the biggest factor in good tumbling is the consistency (viscosity) of the slurry. Too thick a slurry will gum up the process and prevent grinding, and may cause separation of the rocks from plastic pellets (if used). Too thin will allow the abrasives to wash between the rocks ineffectually, while also allowing action that is excessively violent, leading to chipping, pitting, or spalling of the surface, which will make a good polish impossible. The optimum slurry will be tacky enough to hold abrasive grains onto the rocks, but yet allow the rocks to slide past one another.
In the rotary tumbler, the desired action is a sliding down the slip zone (upper 1/3 or so of the load. Rocks (speckled with grit in the coarser stages) should slide upon one another, not roll on one another nor pound one another. This condition is achieved by not including many rocks that are too large for the size of the barrel; and by using a mix of different sizes of rocks; and by maintaining the right viscosity of slurry. Note also that the tendency to chip or pit will be more pronounced if the average rock size is considerably larger than the usual average value of about 5/8 of an inch, because of the greater weight of each rock. this problem can be minimized, When using the usual hobby-size tumbler, by including very few oversize rocks. But when dealing with bigger barrels in which the main objective might be to produce considerable quantities of larger-than-usual gemstones, special measures may be needed. b
Specialized tumbling: Rocks that would not normally be considered appropriate for tumbling, such as 3-inch x ¼ inch slabs, and such as 8 inch bulky rocks, have been successfully tumble-polished, but these will typically require special methods.
We regularly stock the following tumblers:
Lortone tumblers have solid rubber barrels for quiet operation and long life.
Other tumblers, including large commercial sizes, are available by special order.
Call, write, or visit for prices.
We also have crushed rock suitable for tumbling, and abrasives, and books on tumbling and other lapidary arts.
We also stock parts for Lortone tumblers: