I have been meaning to make one of these for ages, but was hampered by not having a motor (or spare laser printer for parts), and not being good at 3D printing. However I had made a promise to the family to polish some amethysts we found on holiday, so eventually push has turned to shove.

There are a couple of other Instructables out there showing how to make a rock tumbler, and they should get all credit for informing me along the way.

What also unlocked this for me was that I had an old inkjet printer that was needing to be thrown out.

Materials Purchased:

110mm soil pipe joiner and 2 end caps (Wickes)
Silicon Carbide off eBay (SILICON CARBIDE GRIT & POLISH PACK– 200g 80, 220 &400 &100g POLISH). you will find this under "Lapidary Materials". Cost me £18.95 with postage.

That is all I bought - the rest was in the garage or ready to be chucked out.

Step 1: Printer Dissassembly

Before starting on the base, I needed to know how big the moving parts would be, and so I investigated the printer, initially hoping to find a suitable stepper motor.

It became clear that the small printer had DC motors, and also a gearing mechanism that I could use.

I was careful not to break anything that may be useful, and the you can see the two main rotating rollers. I thought these would be hard to cut down (although the junior hacksaw made easy work of them). Also I was nervous of not finding any bearings, but in fact I used nylon/plastic from the gearing which works well on the steel rods.

Step 2: Soldering / Electronics

This was so simple. I was expecting a stepper motor, and to have to hook it up to my arduino and write some code, but it was clear that these were DC motors - the giveaway being the fact that there were only 2 leads and no circuit board.

I fed 5v into the motor from a usb cable, and this is all it needs, & I added a switch (eventually swapped out due to it not working properly).

There is also an identical 2nd motor that I have kept in case the other wears out.

It rotated the drum at 23 rpm.

Step 3: Base / Foundation

I want the instructable to be robust and aesthetic, and I have a fair bit of hardwood just waiting to be put to good use. It needs to be compact and simple to use too.

So no need to explain the pictures too much, but a simple oak base, with chamfered edges (allowing easy finger purchase). I re-used the chamfer offcuts to give strength to the two uprights.

An upright on one end to support the rollers and small plastic bearings - this was a bit of a mess, so you can see how I covered up the open holes with a glued cover (this should have been screwed really so that it can be re-entered later if needed.

An upright on the other end to stop fingers getting in amongst the gears and to protect the motor (as well as mount the switch.

Step 4: Finish & Polish

Finally a varnish, add some rubber feet and mount the assembly.

The 110mm soil pipe has a 1-2mm hole drilled in 1 end cap. This is to allow you to remove the end caps.

(ADDED LATER: I have glued steps into the tumbler to increase the 'lift' and therefore the fall of the rocks..... see the comments in one of the other tumbler instructables where there is a description of why this is needed (or at least improves the erosion)).

The Silicon Carbide (SiC) arrived tonight, & I understand that the rocks are covered with water and a few table spoons of SiC. Gaffa tape up the small hole to prevent leakage and let it run, a week at a time.....

I need to update this with my operational experience & some before/after pictures of the rocks!