Monday, January 01, 2007

DIY Rock Tumbler

I've been saving up to buy a rock tumbler for my rockhounding, but to date I've managed to save almost nothing. Growing impatient, I decided to build one for myself.

As far as I can tell, a tumbler is just a canister that rotates with rock and grit inside. How hard can that be? I've managed to begin construction on one for less than $20. They typically cost around $150. Mine has the advantage of being a bit of home schooling in the subject of mechanical engineering for my kids.

The tumbler design is simple. An electric motor will turn a shaft which will rotate a coffee can mounted on furniture wheels. The motor's speed will be controlled by a light switch dimmer. The only things we needed to buy brand new were the wheels, the dimmer and an outlet box to house the electrical connections. Total cost: about $12. For the motor, I went to a thrift store and scrounged around until I found an old Black&Decker corded drill. Cost: about $4. Perfect!

We sawed the handle off of the drill since we no longer needed the trigger and the handle got in the way.

Our tumbler throttle.

The drill taken completely apart. It was filthy inside and needed a good cleaning.

Mounted on furniture wheels, the weight of the can is taken off of the drive shaft.

Once I had figured out how to open it, I had my son take it apart. At this juncture in the project, I hit upon a real brain wave. Household electronics can be picked up at estate sales and thrift stores for next to nothing. Most people are afraid to take their appliances and tools apart because they don't know what's in there and they're afraid they'll never get them back together. I want my kids to grow up without that fear.

I'm going to start buying these and handing them to my son to be totally dismantled and reconstructed after he does his best at explaining how they work. If they never work again after dismantling, the cost will be trivial compared to the education and confidence he will gain. As my daughter grows older, I'll do the same for her. My kids aren't home schooled, but modern schools miss parts of their education like this. Not many kids take shop classes any more.

Enough about home schooling. Back to the project.

My biggest technical hurdle was the drive shaft. I don't know how to weld and I couldn't figure out how to connect the coffee can to the shaft. Finding the drill was a stroke of luck in more ways than one. While at Home Depot looking for the wheels and the dimmer, I came across a turnbuckle. That solved all my problems. By using a spade bit in the drill, I could put the spade portion of the bit into the turnbuckle after having drilled the turnbuckle through the coffee can. Voila! I had the connection between the motor and the can.

The turnbuckle assembled on the can.

The spadebit fits perfectly into the turnbuckle.

The full assembly of the can. It will later be mounted on a 3/4" plywood base.

We're at a standstill right now because the drill needs a couple of pieces. A pair of connectors inside the drill had worn out. I'll be hitting the local DeWalt repair place for the parts tomorrow. I'm sure they'll think me quite mad. That just adds to the fun!

Update: The HCCRT Mark I is done. See the results and definition of the acronym at this post, complete with YouTube video.

For more educational posts, visit the Carnival of Home Schooling. For more posts on saving money, please stop by the Festival of Frugality.


Scribbit said...

That's impressive that you can rig something like that up. I'd be a weenie and just save up my $150. I always wanted one of those as a kid but I always had a feeling that the kid versions wouldn't work at all, being so cheap. I still wanted one though.

Alasandra, The Cats and Dogs said...

Good luck.

I broke down and bought Lord Epa one last year for Christmas, the results were great. Now we need to find some more rocks. The noise is horrible though, luckily we were able to put ours far away from the house down at Hubby's shop.

Scribbit mentioned the kid version, don't waste you money. Been there done that. It's good for the packet of rocks included with the tumbler and that is about it.

K T Cat said...


The coolest thing about this project was to realizie that you could tear things to shreds to understand them and still be a weenie about the ones you used every day. The thrift store was loaded with small appliances for under $5. Estate sales are the same way.

Add to that the magic of the Internet and you can find the schematics for just about anything on line to help figure out what everything does.

My next step will be to go to a used book store and look for one of those "How Things Work" books. That would be a great companion piece to the project.

Unknown said...

ive got tried building this and altered it a bit the only prob i get is that any dimmer i use either goes way to quick or not at all even turn ing it the ever so slightest it will b of then basically blowing on it to turn on when it finally gets a lil power its way to fast ive tried several dimmers and drills and other motors

Anonymous said...

If you think about whats required for a polisher the first thing that comes to mind is it has to run for a long time, and not run fast. any eletric motor for a fan is made to run for a long time at several speeds.
the second thing I think about is the drum must not leak water and it must be light enough and yet still be strong enough to not have a hole worn in it.
I think that most plastic paint or other resealable contaners might work they come in all sizes.
the next think I think about is how much rock do I want to polish?
I have a box of broken black marble I would love to brake up and polish it weighs 20 or 30 lbs. with this kind of weight I will need something big like a 1/2 hp motor. some good caster wheels that will turn easy to lessen the drag, some with bearings maybe.
I could put duck tape on a portion of the drum to give it grip the wheel from the moter to turn it. what do you think?

Markus said...

VERY COOL!!! Thanks for posting this. I'm making one this weekend!!

K T Cat said...

springboard, if you do so, I'd love to see the pictures and hear the results. For me, this was more of a fun project then something that actually worked. I had a great time doing it, but I must confess I didn't make the necessary modifications and go through the two or three more versions to get one that worked.

Stan said...

Very good idea. I uesd a dryer motoer, lawn mower pulleys and pvc. it cost me around $35 for my stuff

K T Cat said...

Stan, that's an awesome idea! Thanks for leaving the comment and adding to the quality of the post.

Anonymous said...

You might also consider a hand held whisk as a power source, mine has 5 speed settings, and with one dough hook attached it mates perfectly with the turnbuckle.

K T Cat said...

Thanks, Anon! That's a great idea!

Anonymous said...

I used a dremel tool on my tumbler, they too have adjustable speeds like an electric mixer and no disassembly is necessary

funx said...

Your plan inspired me, but how do you keep the rocks and media from falling out of the can while it's tumbling? I see two small holes in the tumbler walls and one very big hole at the drive shaft end.

My plan involved a similar arrangement, but with the motor turning a shaft that drove a belt that wrapped around the can. That way I wouldn't have to have holes in the sides.

Your scheme is simpler if I can just see how to seal the can while tumbling rocks, grit, and water.