Tumbler Finish

I'm looking for a way to speed up finishing post machining in my one-man shop. I currently put a scotch-brite finish on my product line and am happy with the look, but need something faster. I've been considering a tumbler. But what sort of finish can I expect? I'm hoping for a satin look and not a dull galvanized look. I'm working with aluminum in this instance.

The finish is dependant on the media you put in the tumbler.
Some people favor walnut shells as a finisher.

You can also tumble with aluminum oxide or other blast media to attain a finish you would achieve in a blast cabinet without much labor. You can also add polish to the walnut shells mentioned above to get a shinier finish. If you want more than just the standard finish you describe it will be a multi-step process.

How big are your parts? Are you just trying to put a finish on or do you want to do a little deburring too?

The only way you are going to figure out how to get what you like is to jump in and buy a tumbler. I suggest buying small one first to experiment with. I got an ultravibe 18 used but very good cond. on ebay for about $100. This will handle about 20lb of media. It is basically just a reloading tumbler but a pretty good one. Even if your parts are too big for this I think it might be smart to make some small coupons to experiment with at this level. Mcmaster has a good variety of medias in smaller quantities.

At the moment I have the ultravibe 18, a raytech which will handle about .75 cu ft or 50lb of media, and a mr deburr which will handle 3 cu ft of media. The trouble with bigger tumblers is that you'll have a bunch of money in media just experimenting. And by the way, if you buy one of the ultrvibe tumblers it will come with a note that it is not to be used wet. I use it wet and it works just fine. I just put a cup or so of compound (soapy water) in. And another thing- if you use household soap go easy. I read a bunch on here before starting. I used too much soap and had suds everywhere.

I am using plastic media first for deburring but as you say it leaves like an almost galvanized finish. I had some parts anodized with just this finish and I think it is a little too course and uneven. I do think they have different grades of plastic though which I have not experimented with.

I have tried several medias for a second step. I have some very smooth ceramic and just got some porcelain media. These leave a nice burnished finish. Still nothing like scotch brite though.

biglord4ever said:

I currently put a scotch-brite finish on my product line and am happy with the look, but need something faster. I've been considering a tumbler.

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YMMV, but I've never had any luck getting that sort of a finish in a tumbler.

How are you currently doing it?

Orange Vise said:

YMMV, but I've never had any luck getting that sort of a finish in a tumbler.

How are you currently doing it?

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You would have to define by what you mean by "scotch-bite" there are quite a few different grades between the pads and wheels. Also how fast you spin the wheels or the parts using the pads can vary the look of the finish. Pressure applied also matters. I can put a matte or a polished finish on an aluminum part chucked in a lathe just by varying the speeds.

There is an awful lot of art to vibratory/tumbler finishing. It's not magic; it's usually perfectly repeatable. But there are an awful lot of variables: finisher type, finisher power, finisher speed, tub shape and size, media abrasive type, media grit, media shape and size, amount of media, amount of fluid, type of fluid, part shape and size, quantity of parts, etc.

Without a lot of experience, it's a good idea to consult either a finisher maker or a media maker with the specifics of your job and get their recommendations.

sfriedberg said:

Without a lot of experience, it's a good idea to consult either a finisher maker or a media maker with the specifics of your job and get their recommendations.

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What fun is that? No one likes to experiment anymore? I don't think there is anything you can't do in a vibratory bowl, it will just take longer than some of the other models.

Orange Vise said:

YMMV, but I've never had any luck getting that sort of a finish in a tumbler.

How are you currently doing it?

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I currently use a red scotch-brite belt on a belt sander.

I'm open to other finishes. I just don't want the dull galvanized look.

sfriedberg said:

....amount of fluid, type of fluid,

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I'd add cleanliness of fluid too. My aluminum tumbler does not have a recirculation system so the fluid gets "dirty". If I keep right on top of it parts come out nice. Let it go too long and the parts get a gray appearance. If it is too bad, I'll just dip them for a few seconds in a caustic etch then rinse. Brightens things right up.

Vancbiker said:

I'd add cleanliness of fluid too. My aluminum tumbler does not have a recirculation system so the fluid gets "dirty". If I keep right on top of it parts come out nice. Let it go too long and the parts get a gray appearance. If it is too bad, I'll just dip them for a few seconds in a caustic etch then rinse. Brightens things right up.

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What kind of caustic etch and where to buy? If I let the aluminum turn gray I just run them in walnut shells to clean them up, but that takes a while and eventually the walnut shells get dirty and need to be changed out.

caustic etch is probably sodium hydroxide, or something that contains it, like liquid drano, note that it will brighten up everything apart from 2xxx and 7xxx series, those contain too much alloying elements that make parts dark/black after etching, if it does happen and you didn't etch it too much, the smut can easily be wiped off with some soap and a sponge

when a customer sends me supposedly 6xxx series parts to be anodized and I call him back to say they are not, they always swear it most definitely is, then I send them this video explaining I KNOW it is not 6xxx

biglord4ever said:

I currently use a red scotch-brite belt on a belt sander.

I'm open to other finishes. I just don't want the dull galvanized look.

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I'm partial to abrasive brushes, like the Nampower from BRM, or equivalent. You can feed them fast as to minimize the hit on cycle time. On aluminum, they effectively "erase" milling marks and create new ones.

Dualkit said:

What kind of caustic etch and where to buy?

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This is what I use....

Pure Lye Drain Cleaner / Opener, 2 lbs. Food Grade Sodium Hydroxide Micro Beads | eBay

Mix a couple tablespoons in a quart or so of water (real process control there!). The parts I do this with are pretty small. Hang them on aluminum or stainless wire and dunk them for a few seconds until the gray goes away to the point I want then quickly into a rinse. I just use plain water to rinse but some prefer a touch of vinegar in the rinse to ensure that the caustic is neutralized. The temperature of the caustic and how many parts you have used it on will affect the time it takes to work.

Orange Vise said:

I'm partial to abrasive brushes, like the Nampower from BRM, or equivalent. You can feed them fast as to minimize the hit on cycle time. On aluminum, they effectively "erase" milling marks and create new ones.

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Now that's an interesting idea! Thanks for the suggestion!

Vancbiker said:

This is what I use....

Pure Lye Drain Cleaner / Opener, 2 lbs. Food Grade Sodium Hydroxide Micro Beads | eBay

Mix a couple tablespoons in a quart or so of water (real process control there!). The parts I do this with are pretty small. Hang them on aluminum or stainless wire and dunk them for a few seconds until the gray goes away to the point I want then quickly into a rinse. I just use plain water to rinse but some prefer a touch of vinegar in the rinse to ensure that the caustic is neutralized. The temperature of the caustic and how many parts you have used it on will affect the time it takes to work.

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Thanks! I tried the drain cleaner idea on some I think was 1018 parts once. Like you my tumbler bowl does not have a drain so it is a PITA to change the fluid. I could never get it right. I think the issue was too strong a mix. I will try your idea, thanks again.

I am a major lurker and have been for a long time on this site. For some cool information on what a tumbler can do for you check out this old thread and others by the late Mitty:

https://www.practicalmachinist.com/...his-nuts-walnuts-157463/?highlight=mitty+nuts

Dualkit said:

Thanks! I tried the drain cleaner idea on some I think was 1018 parts once. Like you my tumbler bowl does not have a drain so it is a PITA to change the fluid. I could never get it right. I think the issue was too strong a mix. I will try your idea, thanks again.

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Just to make sure we are clear here... I don't run the caustic in the tumbler, just as a post tumble dip if needed. Also, I don't know how/what caustic does to steel. I only do it with aluminum.

Vancbiker said:

Just to make sure we are clear here... I don't run the caustic in the tumbler, just as a post tumble dip if needed. Also, I don't know how/what caustic does to steel. I only do it with aluminum.

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Understand that, thanks.

I sent a batch of sample parts to the Burr King test lab yesterday. We'll see what they send back...