TOPIC:

I've been using both the goodies you mention for prepping.
A high concentration of caustic granules and (almost) pure nitric acid after that.
The trick seems to be in the power supply I think...
Easiest thing to dye is actually the (smooth) wire I use to hang the parts in the acid bath :

Too bad - nothing really happened when I attached the Robbe charger to the acid bath.
Other than that I somehow blew the fuse on my multimeter when I tried to measure this and that...
There was about 16-17V between anode and cathode but apparently no noticeable current.
I didn't get to check that but I didn't see any bubblies going on.
That last statement isn't very scientific but it is a giveaway of the anodisation process...

I'll leave it be for now and contemplate on the further approach.

I've been reading up again and it kinda eludes me why the process won't work in some cases.

Edou wrote:

So far I have been using the "constant voltage" method which means using a regular power supply or car battery.
The voltage is set and the current should then run (and vary) on it's own.
But with some sorts of aluminium, this current stops swiftly.
This is because the anodisation process creates a layer on the material that starts working as an insulator.

Reading on Wiki I tend to think that the solution to your problems of the process stopping up would be the to increase Voltage, not the Current.
You say that the anodizing creates a layer of insulation, and I would guess the way to overcome the insulation problem would be to increase the voltage.

The current you use should, apparently, be equivalent of the item's surface being anodized.

So, the power supply you should have should probably have both current and voltage adjustment possibilities.

-Lars

Just a thought, but could it be the electrical connection between the hanging wire & the parts? - looking at the pics & thinking, as you get a buil-up of whatever on the wire, it will affect the connection to the parts, & it'll end up being easier for the electricity to pass from the wire into the bath than to go across a "dirty" connection, into the part & then into the bath, if that makes sense?
Also, what's the wire made from? - it was mentioned somewhere that you mustn't have anything in the bath that isn't either lead or ally (ie, no copper or steel) as it will break down to become "contaminants"

Thanks guys, some good points to think about.
Juicing up the voltage has certainly crossed my mind.
Generally 15V should be enough (from what I read) but it's be an interesting approach to see what happens.
I could do a cheap troubleshoot like that the other way around also...
Which would be to lower the voltage with parts that work well and see how that influences the process.
Eddrick, points of contact aren't great in the picture above but the wire is aluminium from a hobby materials shop.
That stuff anodises really well - maybe too well actually...
I may try a lead cathode too. That's easier to find than high grade alloy.

Off topic @eddrick - I think the TA02 gears you sent have become a lost cause...

To prove your connection between wire & parts, stick the multimeter across the junction on a low ohms scale (200 ohm/beep). Do it before you start, & again when the bubbling stops & compare the readings. Also try a better mechanical connection to the parts, eg twist the wire really tight, or bolt it on using ally fasteners. If the wire anodises really well, that should tell you your bath, volts, amps, polarity & dye are probably ok. That leaves something not right with the connection to the parts, the material of the parts, or the prep of the parts I'd say.

Hmm to the gears, I'll try to get to the post office & interrogate them. It says on the receipt "Airmail", so I would've thought it'd only take a few days. Maybe the plane crashed... (Due to poor anodising?)

This was more of a trial to see how it would go with a connection like this, and to see how this alloy would behave.
I didn't bother to give it a second try with better connections because nothing really happened - apart from the wire.
If I can, I use an aluminium or titanium screw. The setup needs many more steps for improvement...
But only useful if I get the basic process going for all sorts of aluminium.

I do think it comes down to the power supply in the end...
This one is too "light" and I will have to find a specimen that gives a more solid current output.
Like one that is used for slotraces for example.
But maybe that car battery is a good idea after all! I can recharge it with this Graupner...

Like I said, try a laptop power supply - most will do 19v smooth DC at around 3-4A (I actually use a modified 12v one as a power supply for my nicad fast charger, works loads better than the pukka 5A transformer). There are some cheapy generic ones floating about on Ebay for around 10gbp, & most have adjustable output voltage (Mine will do 15-24v at 3.5A & that's the basic version)