Anodizing @ Home

The other night I finally finished buying all the supplies I needed to try to anodize some aluminum parts. Anodizing is a process that causes aluminum hydroxide to grow into and out of the surface of aluminum metal. Aluminum hydroxide is very hard, which provides scratch protection and is also porous which allows dyes to color it. Dying the metal is reason for a lot of commercial anodizing and is the main reason I am doing it.

The basic process of anodizing is to form an electrical circuit between the part to be anodized (the anode), dilute sulphuric acid and (usually) another piece of aluminum which is the cathode. Voltage is passed through the circuit which causes the anodizing to take place. The part is then dyed and finally the pores are sealed to keep the dye in.

This post describes how I did it.

First, some safety. Most of the stuff that I am doing to anodize parts can blind or kill you. Always wear gloves. Always wear goggles. Never mix chemicals unless you know what will happen. A few of these chemicals mixed will produce horrible gases that will kill you and your family and probably your dogs too.

Next, the supplies. I bought the following:

  • Battery acid, 5 gallons, from NAPA Auto Parts
  • Lots of distilled water
  • Several plastic buckets from Home Depot
  • 1 pound tube of 1/16″ aluminum tig welding rod from Central Welding Supply
  • 40 amp battery charger from Harbor Freight
  • Black RIT Dye from the supermarket
  • 2 single burner hot plates from Target
  • 2 6 quart pots for the hot plates

The first step is to get the parts nice and clean. I first washed them in warm water and hand soap and then in a dilute mixture of Simple Green and distilled water.

Next I used the welding rod as simple aluminum wire and attached pieces about 6 inches long to each part I wanted to anodize. You have to make sure the wire is attached very well, and also keep in mind that wherever the wire is attached the metal will not anodize. Lots of people use threaded holes and jam the wire in. I just made some little clips by bending the wire.

Next I took 1.5 gallons of my battery acid and mixed it with 1.5 gallons of distilled water. I kept in mind the AAA rule. Always Add Acid. If you add water to acid the water can boil and “explode”. I put 1.5 gallons of distilled water in a plastic bucket and slowly poured the 1.5 gallons of acid in. Very slowly. Probably took me about 5 minutes.

Next I used some aluminum scrap I had laying around to make a cathode and used some as a rack for the anodes to hang from. It’s pretty clear from the below picture:

I drilled a bunch of holes into the anode rack to use as hook hangers and bent the ends of the anode wires into hooks. Hang the parts.

Next step is to apply the juice! Hook up the negative from the battery charger to the cathode and the positive to the anode rack. I’ve read that it’s best to start at low current and ramp it up. My charger has settings for 2 amps, 10 amps and 40 amps so I set it to 12 volts, 2 amps and let it run for 5 minutes. Almost immediately there were bubbles forming around the cathode. The bubbles are hydrogen gas which comes to the surface. Make sure you have some ventilation so you don’t blow up your house. Remember the Hindenburg.

5 minutes later I turned it up to 10 amps and then 5 minutes later I turned it up to 40 amps.

(I should probably note that I am running this batch as I type this post. Most of the experiences for this post come from a batch I did the other night with slightly different gear. )

At this point I let the anodizing bath run for about 80 more minutes. I have read that anywhere from 45 minutes to 90 minutes is good.

There’s a few ways to tell the anodizing has finished. The current draw should drop quite a bit. An anodized surface does not conduct electricity well, so as the surface becomes more anodized the part conducts less electricity. You may also notice a slight lemon yellow tint to the part. I just let it run for 90 minutes and called it good.

Once the parts are finished, turn off your power supply and rinse the parts very well in cold, clean water. The water must be cold or the parts will start to seal.

Next up is the dye. I used RIT Dye which seemed to work pretty well. There’s lots of places to get proper anodizing dye but RIT seems to work for me. I dumped a bottle the black, liquid RIT into 1 gallon of distilled water and put it on the hot plate. The dye works best heated and most people recommend about 140 degrees so that’s what I used. Once the dye was up to temperature I put the parts in and let them soak for about 15 minutes. I have read that you might get the color you need in as few as 15 seconds depending how dark you want it. I wanted dark, dark black so I left them in for 15 minutes.

At this point you can pull the parts out and you may find that some didn’t take any dye or the dye drips right off. This happened on my first batch with one part. What this means is that you didn’t have a good electrical connection to the part. You can remove the dye and anodizing by etching it in a bath of water and lye. I used a few tablespoons of lye in about a half gallon of distilled water.

Once the parts are dyed the only thing left to do is seal them. This is done with boiling water. I read that steaming the parts before putting them in boiling water can help you lose less dye, so I put a pot of water on my other hot plate, put a rack over the pot and placed the parts on the rack. Then I boiled the water letting the steam wash over the parts for about 10 minutes. Then into the bath they go. 30 minutes in boiling water and the parts should be sealed and ready for use! Hooray!

I’m still a total newbie at this, and I’m actually going to a professional anodizing shop next week to see how they do it. That said, I did get really nice results and it seemed pretty easy. Takes some time and a few dollars but the result is amazing!

My pictures of the finished results are here and Courtney’s pictures of the process are here.

Recent Work and Overheard

So, the other day Courtney and I drove down to Kent cause I got a hot tip on some powdered red jewelers rouge at Jerry’s Rock and Gem. We went in and it was pretty clear from the start that by gem they mean “Crazy people crystals”. This was confirmed when while standing in line I heard the lady next to me (dealing with another clerk) say “Well, you know, if the¬†cataclysm¬†comes I hope you have 4 or 5 big trucks to get all of this stuff to higher ground.”

She said it in hushed tones and you could tell she was just dead serious.

That being said, Jerry’s was pretty cool. They did have the rouge I needed (more about that later) and they had a great selection of tumbling supplies, petrified wood sculptures, all kinds of interesting minerals and all kinds of rock and gem related stuff. Neat place.

So, since my last post about my clock I’ve been working on my clock and one other thing. For the clock, I decided I would make 5 total, complete clocks and then be done with it forever. The clock has a lot of parts to make a single enclosure so I spent some time trying to speed up the process of making some of the parts.

One of the components of the clock is these tiny 1/4″ polished aluminum rings. I made the first 8 for the original clock by hand but it took forever and was very difficult. I cut the little pieces of my bandsaw and then bored them out on my drill press but the parts are so small it was difficult to get them in a vise without ruining them.

So, what I did this time is I made a “ghetto lathe”. I took a piece of 1/2″ aluminum plate, drilled a 1/4″ hole and a few 10/32 tapped holes and then a 10/32 tapped hole in the side to intersect with the 1/4″ hole. Into the 1/4″ hole went a stubby 1/4″ drill and I put a set screw in the side to hold it. In one of the tapped holes I put a lathe tool post and a lathe cut-off tool. Then I put my polished tube stock in the chuck of my mill and wrote a program. The program would push the spinning stock down on the drill to bore it out and then run it against the cut-off tool to cut off a perfectly sized ring. This worked perfectly! I made the 40 rings I needed in just a few hours. There’s a video of the process below.

The next thing to do was to make the 40 metal plates that make up the body of the clock. Each clock uses pairs of 4 different shapes for 8 pieces each. I made a little fixture out of MDF on my mill and cut these all out in the course of one long Saturday. Nothing special there.

The special part was that I did not want to hand sand all of those parts, so I went to Harbor Freight and picked up a 18 lb vibratory tumbler for the low, low price of $149 and set to learning how to use it. I got some plastic triangle media from a local friend and threw in my parts in batches of 10 for about 6 hours each. This put a nice matte finish on the parts, rounded all the corners and removes burrs, which was great! After that I used walnet shell media with the aforementioned red rouge to polish the endcap pieces as these will be anodized. I let those run for about 36 hours and they came out very nice. A few steps from a “mirror” finish.

Now I am at the anodizing stage. I’ve done a lot of reading and I feel like I will try doing it myself. I picked up a bunch of plastic buckets at one of my nearly daily Lowes trips the other day, got some lye yesterday, got 5 gallons of sulphuric acid today and need to pick up a few more supplies tonight. I’ll probably wait till the weekend to give it a try and assuming I have some success I’ll write a post about how that works.

My next project, and the one I expect to consume me for the rest of this year and maybe longer is OpenPnP. I decided that I would like to own a small pick and place machine for doing PCB assembly but I don’t like the $30,000+ price tags. I figure this is something that would be fun to build and maybe in the mean time I can revolutionize home PCB manufacturing! My hope, and goal, is to design and build a fully functional pick and place machine that that can reproduced for around $1,000. I will make all the designs and software open source and maybe, if there’s interest, produce some kits or something.

OpenPnP is still in it’s very beginning stages. So far I have bought a few basic parts and I’ve been making some parts on my mill. My goal for this month is to have a working, high precision 2 axis “cartesian” platform and to be working on adding motion control. My target is to get a basic 2 axis CNC made so that I can start working on the head design, which is where all the hard work is going to be. The CNC doesn’t need to be complex, but it needs to be precise and fast. To that end I am using THK linear guides for X and I am considering Hiwin linear guides for Y. I bought the THK guides off eBay to get started but will probably spec Hiwin for both axes in the final version.

So, that’s what’s new. I’ll be posting quite a bit about OpenPnP over the next several months. Now that I have officially announced the project I intend to document my progress as much as possible.

In the mean time, if you are interested in OpenPnP please go to it’s homepage and read what I have there. I am currently interested in talking to people who have experience with computer vision systems as I expect that to be a very difficult part of the system.