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Detailed Review of the Thumler's Model MP-1 Rock Tumbler

This review was prepared by Hobart King, Adam Rittenhouse, and Angela King of - an online store that sells everything that you need for rock tumbling. They also publish the Rock Tumbling Library.
Thumler's Tumbler MP-1
Tumbler Model: Thumler's MP-1 Rotary Rock Tumbler Kit
Brand / Manufacturer: Thumler's Tumblers / Tru-Square Metal Products
What You Receive: Thumler's MP-1 Rock Tumbler Kit includes: the tumbler; a rubber tumbler barrel; a booklet titled "A Guide for Rock Polishers"; a grit pack that contains the grit and polish needed to tumble one batch of rocks (packets of coarse, fine, pre-polish and polish are included); a package of rocks that are properly sized for this tumbler; and, a packet of jewelry findings that will enable you to make a necklace with pendant, a keychain, and a pair of clip-on earrings using some of the tumbled stones that you will produce. More photos below.
Barrel Construction: A soft rubber barrel, with a plastic lid, that seals with a retainer ring. The inside shape of the barrel is a 15-sided polygon. The 15-sided shape of the barrel produces a gentle increase to the tumbling action when compared to a barrel with smooth sides.
Barrel Dimensions: Outside: 5" diameter, 3" height
Inside: 4 1/4" diameter, 2 5/8" height (floor to lid seat)
Barrel Volume: Approximately 20 U.S. fluid ounces (600 milliliters)
Tumbling Capacity: This tumbler is intended to process about one pound of material (rocks, or, rocks plus media).
Tumbled Rock Size: The MP-1 tumbler works best when tumbling rocks and minerals that are in pieces that range from about 1/4" to 1 1/2" in size.
Base: Molded plastic
Tumbler Rating: We rate this to be a "Beginner's Rock Tumbler". More information.
Barrel Speed: 50 RPM, 667 inches per minute inside. This speed will produce bruising and breakage in many types of rocks that are commonly tumbled.
Rock Type Performance: The Thumler's MP-1 Rotary Tumbler can tumble most jaspers, agates, and other materials with a very high tenacity (resistance to breaking, bruising, falling apart) into nice tumbled stones with no accommodation for the speed of the tumbler.

The MP-1 can tumble some materials with a brittle tenacity into nice tumbled stones if they are cushioned - with at least 50% of the load being cylindrical ceramic media under 5/8" in size. Without cushioning media, these materials might be bruised or broken. Materials that bruise or break include: varieties of macrocrystalline quartz (amethyst, rock crystal, smoky, rose, etc.); varieties of granular quartz (quartzite, aventurine, etc.); tiger's-eye, beryl, granite, unakite, and similar materials.

Even with ceramic media, bruises and breakage will occur with many brittle materials (including the ones listed above). The larger the pieces, the more likely that bruising or breaking will occur.

Rocks that cleave easily will often be broken in the MP-1 tumbler, even if they are tumbled with at least 50% of the load as ceramic media. These include: labradorite, moonstone, orthoclase, amazonite, sunstone, and other varieties of feldspar; fluorite, topaz, and calcite. A tumbler with a slower, gentler tumbling action will work better for these types of rocks. We usually use a vibratory tumbler with these types of materials - especially during the medium grit, fine grit, and polishing steps.

The MP-1 tumbler is not a good choice for tumbling man-made glasses and natural glasses (such as obsidian and Apache tears) and granular aggregates (such as apatite and olivine). These materials will usually be broken or bruised - even if they are tumbled with ceramic media. A tumbler with a slower, gentler tumbling action will work better for these types of rocks. We usually use a vibratory tumbler with these types of materials - especially during the medium grit, fine grit, and polishing steps.
Replacement Parts: With proper use and maintenance, this tumbler should last for years. Some parts - such as belts and barrel lids - may need occasional replacement. Replacement parts (belts, barrels, lids, retainer rings, bearings, guides, retainer clips, rollers, motors, drive shafts, idler shafts) are available from the manufacturer and some vendors.
Operator Maintenance: Each of the four bearings should be lubricated with one drop of SAE 20 motor oil, or one drop of household oil, once per month, or after every batch of rocks is tumbled. Bearings should be cleaned with soapy water if dirt or oil residue accumulates. Instructions for this easy job can be found here.

The belt and pulley grooves should be cleaned with a rag dampened with soapy water (or a Q-tip) if evidence of dirt or grease is noticed. Instructions for this easy job can be found here.

Motor lubrication is not required.
Operating Environment: This tumbler should be operated indoors, in a space where temperatures do not drop below freezing. Do not operate in a damp or dusty location. See our article about "Where to run your tumbler?".
Minor Issues: We purchased one of the early MP-1 tumblers in 2009 and have used it to polish dozens of loads of rocks. We have also sold thousands of MP-1 tumblers to customers of between 2009 and today.

The most common customer complaint is that the barrel lid wears thin from the moving rocks in the barrel, and a hole eventually develops in the center of the lid.

To avoid making a mess, we test our lid with thumb pressure before placing the lid on the barrel. Too much flex in the lid warns that the lid is thin and might wear through, so it is time for a new lid. A lid lasts us through many batches of rocks. Large angular rocks and filling the barrel too full are particularly hard on the lid. We have an article that provides some suggestions here (see item #6).
Author of this Review: This review was prepared by Hobart King of I have been using rock tumblers for over 50 years and have been the owner and manager of since its founding in 2009. We are retail sellers of rock tumblers and rock tumbling supplies.

I purchased an MP-1 tumbler when it was first released in 2009. After using it to tumble several batches of rocks, I was satisfied that it was an excellent tumbler, and we started selling them in early 2010. Since then we have sold thousands of MP-1 tumblers. We have also used that original MP-1 tumbler to test many of the roughs that we sell - and it is still running fine.

We are proud to sell this tumbler because it does a great job tumbling rocks, stands up well after years of use, and produces very few customer complaints. If this was not a good tumbler, we would not be selling it. I have interacted with lots of customers who use the MP-1 rock tumbler, and I believe that I am a qualified person to write this review.