Pier 9 Guide: Making Your Metal Parts AWESOME by Tumbling

This Instructable is for Workshop Users at Pier 9.

Requirements for using the Tumbler at Pier 9:

1. Read through this Instructable
2. Talk with Shop Staff about your project and make sure your parts are appropriate for the tumbler.
3. No copper-bearing metals in the tumbler! That means brass, bronze, etc.

*: [Seinfeld voice] Not that there's anything wrong with that.

Are you making parts in metal? Do you want them to look clean and smooth, but instead they have marks all over from grinding and scribing, or sharp corners from cutting or machining, or welds in hard-to-reach spots that would take hours of filing to clean up? The tumbler is the tool for you!

This Instructable is specifically a guide to using the Tumbler at the Pier 9 Workshop, home of Instructables, but if you are looking to take your metal parts to the next level, this Instructable can be a resource for you as well.

What is a tumbler?

You may be familiar with rock tumblers that run for weeks to wear down and polish the surface of rocks. Metal parts tumblers work in a similar way: abrasive media and water, along with parts, are put in a rubber-lined bin that is either rolled or vibrated to rub the media against the parts. A detergent or compound in the water helps keep the media from getting clogged with metal sludge, and the surfaces of the parts get worn away: sharp edges are broken, surface discoloration and blemishes are erased, and your parts come out smooth, homogeneous, and beautiful.

There are rotary tumblers (like rock polishers) and vibratory tumblers, sometimes called deburring tanks. Removal of burrs (sharp edges) is the primary goal of most tumbling operations, but with the right media you can even mirror-polish parts. A small rock tumbler will work fine, albeit a bit slow, for metal parts, but at Pier 9 we have a 1.5 Cubic Foot Vibratory Deburring Tank that can handle parts up to 16" long

Parts

Your parts should be non-copper-bearing metal*. Tumbling media is like sandpaper: it will even cut hardened steel (slowly). Jewelers often tumble sterling and even gold parts in small rock tumblers. Your biggest limit is size: the tumbler at Pier 9 has a 1.5 cubic foot capacity and measures 18" x 12" x 12". Although there are few hard-and-fast rules for filling tumblers, keep these points in mind:

-A tumbler is most efficient between 75-90% full (parts, media, and water combined).

-You'll want between a 1:3 and 1:5 ratio of parts to media by volume. In other words, if you have 10 cubic inches of parts to tumble, you'll need between 30 and 50 cubic inches of media. How do you measure that, you ask? You eyeball it, that's how. Don't worry too much, just make sure you have mostly media and you haven't filled the tank more than 80% or so. Don't forget: there's water too.

Media

Tumbling media comes in ceramic and plastic. Ceramic is usually for steel and plastic for aluminum. Media comes in different shapes, sizes, and grits (see McMaster Carr's selection here). Don't be afraid of coarse media: it may still take hours and hours to get your parts tumbled sufficiently.

At Pier 9 we have:

• 7/16" V-Cylinder "Smooth" media
• 1/4" Triangular "Polished" media
• Walnut Shell media for polishing soft metals

Media is located in the Project Container when not in use.

Media will attack the edges of your parts more aggressively than the flat surfaces, just because the edges are more vulnerable to abrasion. If you have excessive deep marks on the flat surfaces of your parts, they could take days to tumble, so consider grinding them with fine sanding belts/discs first if possible.

If you are picking your own media, choose a size that will get into all the nooks and crannies on your parts that you want tumbled, but make sure the media won't get lodged in your parts. It can be a pain to unstick dozens of little abrasive chunks from your work, not to mention those plugged areas don't get the same tumbling action as the rest of the part.

*- This is only a requirement at Pier 9.

Water

You want to use as little water as necessary to allow the parts to tumble efficiently. This is a trial-and-error learning process, but generally speaking you want to put all of your parts and media in the tumbler, then fill it with water until everything is submerged slightly.

Compound

Burnishing compound is a detergent/lubricant that keeps the media clean and keeps oils, metal particles, and other contaminants suspended in the water so that the media and metal can interact how they are supposed to. You only need a small amount of compound, usually a couple teaspoons for a small tumbler (but follow the manufacturer's recommendations).

The burnishing compound we have at Pier 9 is Vibra Finish VF 150, a slightly acidic mixture with rust inhibitors to prevent steel from oxidizing. You will want approximately 1.5oz. of VF 150 per gallon of water used.

Getting Set Up

The tumbler at Pier 9 is located in the Hazerdous Materials cage at the rear of the pier. Before you can load the tumbler, there are a few things to do:

1. Fill a bucket with water. There should be a bucket under the drain valve on the tumbler.
2. Tell shop staff that you're planning to use the tumbler and have them open the Project Container so you can get media.
   
3. Make sure the tank is "clean." You're never going to get it sparkling, but at least clear out any solid material (a small amount of sandy grit left over from the last operation is fine), and drain as much water out as possible. Pour some clean water into the tank, swish it around, and drain it out.
4. Make sure you close the drain valve before you proceed!

Loading

1. Put a little media in the bottom of the tank first. Depending on how many parts you're putting in, you may want to layer parts and media like a sundae so that the media can begin its work immediately. Even if you just dump everything in, it will eventually mix itself up and do what you want it to, so don't worry about this too much.
2. Load your parts and media (remember, 1:3 to 1:5 ratio of parts to media is ideal).
3. Fill the tank with water until everything is just submerged. Pour in a bit of compound (1.5oz. per gallon of water approximately).
4. Clamp the tank shut with both clamps.

The control box for the tumbler is bolted to the ground off to one side. It has a timer dial so you can have it automatically shut off after some minutes (up to an hour), or just set it to "On" and come back on your own time.

1. Make sure the power cord plug is plugged in correctly.
2. Turn the timer dial either to "On" or whatever time you want (if you're setting the timer, turn it most of the way around and then back down to the number of minutes you want; otherwise it will not work).
3. Turn the tumbler on and cover the switch with the E-stop cover (don't press the E-stop down or it will shut the tumbler off)

The tumbler will rattle a bunch as it gets started, but after 10 seconds it will even out and start to hum. You can leave the cage now.

If this is your first time using the tumbler, don't leave the Pier while it's running. Overnight tumbling is o.k., but shop staff needs to know in case something goes wrong.*

After an hour or two, shut the tumbler off and take out a part. Rinse it off and take a look. You should see that the edges have been knocked down and the surfaces are starting to even out. If your parts are mild steel with mill scale, you will see the scale starting to be worn down.

If your parts look how you want them to look, congratulations!! You can proceed to Clean Up!!

If they're not there yet, seal the tank and turn it back on. Depending on your goal, tumbling can take between 1 hour and 2 days.

* -For overnight tumbling, make sure to write your name and information on the board at the gate. That way security will not freak out, and they will know who to contact if something goes wrong.

Just because your parts are done doesn't mean you are!

1. Drain the watery slurry out of the tank into a bucket. Close the valve.
2. Using a hose or the rest of your clean-water bucket, fill the tank back up. Seal it, turn it on for 10-20 seconds, then open the valve with the tumbler on. Let it vibrate and drain into your bucket.
3. Repeat Step 2 once or twice until your water comes out clear (you will probably end up with 2 mostly-full buckets).

4. Scoop out your parts and the media into a different bin or bucket.

5. Put the media back in the bin it came in. It's ok if it is wet.

6. Separate out your parts, and take them into the shop and rinse them off in the shop sink.

7. Empty your runoff water into the Waterjet bed.

8. Put everything back where you got it (media bin to the Project Container, bucket under the drain tube, compound on the HazMat pallet, etc.)