Quick Start (Rotary Tumbling)

By Alan Silverstein, ajs@frii.com.
Last update (this page): March 16, 2008

If you just obtained a rotary (not vibratory) tumbler and want to get started as fast as possible, read this section and go play.

• Fill the barrel 2/3 to 3/4 full of rocks. All the rocks should be small enough to tumble without getting wedged in the barrel. For best immediate gratification use hard, solid, silicified rocks like agate or jasper (including most fossil wood), and don't mix in softer rocks like calcite, quartz (hard material but it "frosts"), or feldspar.

• Add coarse silicon carbide grit (described such as "30", "60/90", etc, for the grain size). I use 4 tablespoons (volume) for a 3-pound Lortone barrel, and 8 ounces (1 cup) for a 12-pound Lortone barrel.

• Add water, enough to nearly cover the rocks. Ensure the lip on the barrel is clean.

• Seal the lid per the manufacturer's directions and start tumbling. Ensure the lid is on tightly and evenly. Wait one week. Keep an ear on the tumbler occasionally and glance at it once or twice a day. If you are away from home for more than a day, turn off the tumbler while you're gone and resume when you get back. (I keep paper handy to log the start date, etc.)

  Notes:

  • Rock tumbling makes a little noise. Put the tumbler someplace where the noise is hidden or at least muffled to a nice waterfall sound you can enjoy rather than hate. Also pick a place that's not cold enough to freeze the contents of the barrel, as cool as possible to be nice to the motor, not too dusty, dirty, or wet, and safe from bugs, kids, and pets.

  • If you underfill the barrel it sounds noisier. If you overfill it, it makes a lot less noise and the tumbling doesn't work well. You'll figure this out pretty fast with experience.

  • Many instruction manuals say to check the rocks more frequently than weekly. This is messy and really unnecessary. My experiments say only a trace of coarse grit remains after 5-6 days, and none after 7 days.

  • Many instruction manuals say to burp the barrel periodically. This is also unnecessary, the only exception in my experience being bottle glass, it does "outgas" and expand the barrel. All other materials I have ever tumbled seem to dissolve some of the gas, rock, or grit, such that the barrel ends actually suck in during the week. Just keep an eye on the bottom end of the barrel for bulging out (bad) or sucking in (not a problem).

  • Timing is not critical with rotary tumblers. You can mess with them a day early, or let them run several days late if you get too busy to mess with them.

• Open barrel, wash thoroughly: Lid, barrel, rocks. Do not pour the slurry down the drain, it will clog your pipes. The simplest method is to catch it in a bucket (ask for free "bakery buckets" at a supermarket), let it settle, and pour off the nearly clear water. Gather dense slurry until you have enough, set it aside to dry thoroughly, and trash the resulting "mud brick".

  I scrub the edge of the lid and the lip of the barrel with an old toothbrush. I also make sure to get all the slurry and grit out of holes and crevices in the rocks when going to a finer grit.

• Study the rocks. Are they smooth enough to make you happy? If not, repeat another week with coarse grit. Otherwise go on to fine grit. It can take 1-4 weeks of coarse grinding depending on how smooth your rocks are to start with and how rounded you want them to be when polished. (I like my rocks well-rounded...)

  Note, I have enough rocks in the process that every time I dump the barrel from a coarse load, I sort the rocks into at least three classes:

  1. Ready to polish.
  2. Needs more coarse grinding.
  3. Junk, throw it away.

  But especially if you are tumbling all identical rocks it's fine to never sort them, and just repeat coarse grinding the whole load one week at a time until you think they're mostly ready to polish. In this case, start with the barrel kind of over-full because the rocks "shrink", mostly during coarse grinding, and you need enough to work well in the later stages.

• Finish polishing. When you have a "full" load of rocks ready to polish, run them a week with fine silicon carbide grit (like "220"). Then run them a week with "pre-polish compound" (a coarse metal oxide powder), and finally a week with "polish compound". For the latter I prefer cerium oxide, but tin oxide is good too. I find alumina (aluminum oxide) doesn't work well.

  Note well, you must dump the slurry from the coarse and fine runs, but you can reuse -- a lot -- the more expensive prepolish and polish compounds, as described elsewhere.

• How'd it go? If you wash and dry rocks from the final polish step and they are not shiny enough to please you, there are several possibilities:
  • Wrong kind of rocks. Some rocks are just too soft or irregular, or tend to end up "frosted". It's still fun to experiment. If at least one of your rocks in a load is nice and shiny while others are not, probably the others won't take a shine, or at least need special handling.

  • Need more polish time. Try running them several more days, or even another week, with polish compound. Another trick I use is to just get "lazy" and let the polish runs go a bit long on purpose, like 8-9 days.

  • Contamination. Are you sure you got the rocks and the barrel and lid totally clean between steps? Traces of coarser grit can mess you up.

  • Broken edges. Sometimes a crack in a rock will break apart late in the game, and the new, rough edges mess up other rocks in the load. This is disappointing but easy to fix with more tumbling time.

• Remember to lubricate (oil) your tumbler as the manufacturer recommends. On my 3-pound unit I oil the shafts once a month with 10W30 motor oil from an eye dropper bottle, and the motor only rarely when it squeaks, as described elsewhere. On my 12-pound unit I oil the shafts about every two weeks and the motor about every three months.