How to strip and reanodise faded fork caps

[suzyj]

Here's a guide to strip down and reanodise your fork caps.  My forks are 998 Showas, of about '02 vintage.  Much of this tutorial applies to any forks, and indeed to any anodised aluminium part.

I was getting annoyed at the orange and faded blue caps and adjusters on the top of my forks.  I'd bought them used to replace my Marzzochi's but apart from new oil and springs, hadn't done anything to them.  There were other bits on the bike I wanted to reanodise, do I figured I'd make a job of it.

Firstly, I collected the gear:

• Tools for disassembly and reassembly (notably a 32mm socket to get the cap off, plus sundry other sockets and allen keys)
• Some bowls and tubs to put the various chemicals in.  I used chemical-safe plastic and glass.  Some of the chemicals are pretty nasty.
• Sodium hydroxide (aka caustic soda or lye) for stripping the anodising.  I bought some granules from the supermarket.
• 10% sulphuric acid.  I used lab grade stuff, but am told that battery acid from automotive stores is around 20%.
• Dyes.  I bought mine from Caswell plating, and used Deep red, Blue 4A, and HBL black (for other parts).  They were the most expensive part of the project.
• A power supply.  The highest voltage I saw was 8V, and the highest current I used was 1.2A.  Something where you can set a constant current is good.
• Plenty of de-ionised water for rinsing parts.
• Some aluminium welding wire for making brackets for holding stuff in the anodising solution, as well as some sheet aluminium to use as a cathode.

I started by removing the fork caps.  Step one was to get the weight of the bike off the front wheel and undo the caps with a 32mm socket.  Then once the caps were free I lifted the front wheel to push the caps out of the forks.  Here's the setup I made to compress the spring, so I could get to the nut under the fork cap to undo it.



Here's the cap with the preload and damping adjustment kit still attached:



So once the cap is out with it's damping rod etc, the disassembly work begins in earnest.  I started by holding it in aluminium vace jaws, and screwing the damping adjuster in clockwise until it came out the bottom.



Then I turned the preload adjuster clockwise to reveal the little circlip on the blue bit.  Once this was removed, I was then able to undo the preload adjuster and pull it out.  



Then I separated the blue center piece from the red cap, and removed all the sundry o-rings etc.  Here's all the odds and sods disassembled on the bench:



After a really good clean and degrease, it's time to remove the anodising.  I just added a tablespoon of sodium hydroxide to a litre or so of water, and waited until all the sodium hydroxide had dissolved.  Wear an apron, thick chemical proof gloves and eye protection here.  Sodium hydroxide will cause really nasty burns if you get any on your skin.  Have plenty of water nearby in case you get any on you.



Now drop a part in, and wait.



After a couple of minutes, it will start to bubble furiously.



Take it out then and rinse it under tap water.  I found some of the bits turned rather black once the anodising came off.  This is due to silicon in some aluminium alloys, and is called smut.  Elbow grease with a fine blue scotchbrite pad and some dish detergent removes this.

Here are the raw aluminium parts after clean-up:

[suzyj]

Now for putting coatings back on.

First I set up a bath of sulphuric acid.  This is about 10% concentration acid in deionised water.  Importantly add the acid to the water, not the other way around, which is much too exciting.

I just used a big sheet of aluminium as the cathode (connected to the -ve side of the power supply).  I screwed some welding wire into a handy tapped hole in a test piece (actually part of my clipons) and went to town.  Current is supposed to be 12A per square foot of metal, for 45 minutes.  Estimating the surface area of complex parts requires lots of guesswork.  Anyway, I used between 0.4 and 1.2A for all the pieces I did.



Here's my test piece in the bath:



After anodising, it gets a quick rinse in cold deionised water and goes straight into a pot of dye at 60 degrees celcius for about 10 minutes.  



Then the final step is to boil it in water on the stovetop for another ten minutes or so to seal in the dye.

So having done some test pieces in black, I had a try with one of the red caps.  I added an aquarium bubbler to help agitate the bath.



The red dye was a disappointment though - the colour wouldn't go any darker than reddish pink.



So I decided to change the colour scheme, and have silver caps, with black preload adjusters.

After stripping the red off, I repeated the process for each of the six pieces.  I used a scalpel to score through the anodising to better show the preload adjustment lines.  The end result looks like this:



Reassembly was a reverse of disassembly.



And then finally I reassembled the rest of the forks.  I think they turned out okay.  Not exactly what I intended, but they look cool on the bike.  Certainly heaps better than the original look:



The caps are a reasonable match for the steerer cap.

[Raux]

  

freaking awesome

love the black and silver better

[Anchorism]

So roughly how much is the cost to do something like this?

[suzyj]

So roughly how much is the cost to do something like this?

$50 for the black dye, $20 each for the blue and red (which I didn't end up using).  $3 for the sodium hydroxide.  Everything else was scrounged.

I've got enough dye left to last me the rest of my life.

[Raux]

would this be considered hard or normal anodizing. ie will it fade to purple?

[suzyj]

would this be considered hard or normal anodizing. ie will it fade to purple?

It's normal anodizing.  I believe that you need to cool the acid tank in order to do hard anodizing, and that seems like hard work.

As for fading, time will tell.  From what I've read, the fading is down to the UV stability of the dyes used.  I went for dyes that are specifically made for anodising, so hopefully it'll be reasonably durable.

[Speeddog]

What's an approximate cost of a suitable power supply?

[suzyj]

http://jaycar.com.au/productView.asp?ID=MP3086&keywords=power+supply&form=KEYWORD

This would be entirely suitable.  You can also use a battery charger with a rheostat and ammeter to set the current.

[mattyvas]

You are freaking amazing Suzy.
So many things you do I just dream of, maybe one day I'll be able to do 1/4 of what you take on with your bike.

[Slide Panda]

First I set up a bath of sulphuric acid.  This is about 10% concentration acid in deionised water.  Importantly add the acid to the water, not the other way around, which is much too exciting.

^^^ Important tip!

It's normal anodizing.  I believe that you need to cool the acid tank in order to do hard anodizing, and that seems like hard work.

As for fading, time will tell.  From what I've read, the fading is down to the UV stability of the dyes used.  I went for dyes that are specifically made for anodising, so hopefully it'll be reasonably durable.

Yep - type 2. Type 3 is the hard coating which is harder to do, more costly and only comes in dark greys.

And it's all about the dye. If you use crappy stuff that won't hold up to UV, it'll fade fast. If you want a nice black you should find out who Rizoma sources their anodizing too and use what ever dye they use. What ever it is, it's the most fade resistant dyes I've seen.

And it wasn't mentioned - but you don't need to dye parts to anodize them. The fork cap Suzy did is now just as anodized as the black bits - it's just what shops refer to as clear or natural.

[suzyj]

And it wasn't mentioned - but you don't need to dye parts to anodize them. The fork cap Suzy did is now just as anodized as the black bits - it's just what shops refer to as clear or natural.

I used a very special clear dye for that.  It's not widely available, but I have a limited quantity for just $100 per floz.  1 floz can be diluted with deionised water to make as much dye as you need.












Just kidding.  As Sad Panda alludes to, the clear anodised bits are anodised and sealed, skipping the dying part.

[DucHead]

Very cool!      

[lukevo]

Those fork caps turn out bloody awesome ,

No knowing anything about anodizing....how hard would it be to anodize smaller items such as crank case bolts ? Would anodizing cause a metallurgical weakening?

[suzyj]

No knowing anything about anodizing....how hard would it be to anodize smaller items such as crank case bolts ? Would anodizing cause a metallurgical weakening?

Only if your crankcase bolts are aluminium or titanium.  Anodising doesn't work with steel or stainless.  I hope you're not using aluminium crankcase bolts.

With titanium, you can get all sorts of different cool colours without dyes, simply by varying the thickness of the oxide layer.

Anodising doesn't affect the strength of the part, as it's only adding a layer of aluminium oxide 20um thick or so.