A short film sharing what I’ve learnt about low current density anodising of aluminium from my limited experience in the home workshop. This isn't meant to be the right way, or even a good way, it's just the way I do it.
The technique provides a measure of improved durability / corrosion resistance to parts, as well as changing the aesthetic.
Note: The chemical baths can be reused over and over, so no need to remix for every job.
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00:00 - Materials used in this film may now be hard to source in the UK
00:30 - The importance of surface finish of the part
01:34 - Beware hazardous chemicals
01:50 - Dilute your chemicals the safe way
02:53 - Calculating sodium hydroxide etch bath dilution by weight
04:30 - Calculating sulphuric acid anodise bath dilution by weight
07:28 - Discussing anodising dyes
08:57 - Powering the anodising circuit
09:25 - A simple magnetic stirrer
09:45 - Cathode material and layout
10:21 - Estimating the surface area
11:03 - Using the 720 rule to set time and current
11:15 - Connecting the part to the anodise circuit
11:55 - Cleanliness is next to godliness
12:47 - Pre-anodise etch
13:02 - Setting the power supply
13:13 - Completing the circuit
13:57 - Dying the part
14:27 - Hot water sealing
14:40 - The finished part
Useful links and further reading
Changes to the rules surrounding the supply and possession of sulphuric acid in the UK during 2018:
www.gov.uk/government/publica...
and
assets.publishing.service.gov...
For those speculating about the reason for the withdrawal of concentrated sulphuric acid products from general sale in the UK, this article might give food for thought:
www.bbc.co.uk/bbcthree/articl...
• Acid Attacks In The UK...
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Using sodium bisulphate in place of sulphuric acid:
www.observationsblog.com/scien...
• Anodize and dye alumin...
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A 15% acid solution seems to be what many people aim for. There’s pros and cons to higher and lower concentrations but they’re beyond the scope of my little setup. finish.com has a wealth of information:
www.finishing.com/11/30.shtml
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Some 720 rule calculators.
The one featured is by ‘kreutz’, mainly as I can use metric sizes with it. 1 mil is an optimistic coating thickness for sulphuric anodising -thicker coatings require hard anodising which is beyond the scope of this film.
chemeon.com/p/calculator/
www.hobby-machinist.com/threa...
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POST UPLOAD UPDATE:
Some overseas viewers seem annoyed that the UK government would take steps to try to ensure the safety of their citizens by making it more difficult to obtain something that (a small minority of) the general public has demonstrated they're too stupid to have free access to. I dare say the persistent shopper will still be able to obtain it, but I wanted viewers to be aware of which side of the law both buyer and seller will be on if the relevant paperwork is not available.
I should probably have said “small quantities of clean lead sheet are surprisingly hard to get hold of”. I've since obtained some from a friendly roofer 😉
I’m not a chemist, but I believe having too little acid to mix to the original calculation left me with a solution of around 14.5%. Given my ball park approach, I didn’t think it was worth the re-calculation / re-weighing / re-filming for a such a small difference. With concentration, time, temperature, current density and material all playing a part (and being beyond the scope of my simple setup) I just wanted to get on with it. Note: You can’t just divide the weight of acid by the weight of water to get a percentage, it needs to be the weight of acid by the weight of solution (i.e. acid plus water).
I've had a few messages about MEK. Whilst not to be taken lightly, some comments might be an over reaction:
www.gov.uk/government/publica...
Both etching with sodium hydroxide and anodising liberate gas. In a well ventilated workshop for a short time I see no issues. If you're in a sealed room for a long time, it may be something to take into consideration.
Here are a few other clips where I use the same setup, with pretty good results: • Mini Lathe Cross Slide...
• Machining and Casting ...
• An Improved Work Light...
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Manually subtitled for accuracy (click the CC box)
Shot: DMC-TZ30 1280x720 50P AVCHD
Edit: FCP7 ProRes 422
Mic: C01U