Author Topic: Anodising Aluminium - my setup that seems to have worked.  (Read 18234 times)

Offline raynerd

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Anodising Aluminium - my setup that seems to have worked.
« on: December 17, 2009, 10:59:47 AM »
I have recently been making a pen for my dad for Christmas and someone mentioned that I need to anodise it before I give it to him otherwise the surface will scratch too easily and be too soft. I haven`t ever looked into this and dipped my toe in the water for the first time yesterday with some success and then I did it again today, learning from my mistakes and improving my method. I`ve not looked into the Chemistry properly yet but since this is an electrolysis in 20% sulphuric acid, your basically breaking up acidified water into Hydrogen and Oxygen and since the aluminium is attached to the +ve anode where the oxygen is attracted to, I can only presume you are forcing oxidation of the surface of the aluminium. The cathode (-ve) is made from lead and allows the Hydrogen to form at the other side.

So the setup was very simple, a beaker, 1.5M Sulphuric Acid, power supply 12v maximum 4A, some wires and a lump of lead. I took pictures at each stage but just a little interesting bit to kick us off! The final oxide layer has pores in it until it is heat sealed. These pores allow you to add a stain into the pores and colour the aluminium with an organic dye. I tried this yesterday and stained my aluminium blue but I had a thought today, what if the stain dyed non-anodised aluminium and then my proof of anodising is lost!   

My scrap piece of ally, decent finish on one side not great on the other. Just a scrap from the metal bin.


Dipped in the dye for 5 minutes and removed


Success the dye washes off! This is fantastic, I now know that if my dye does stick at the end then I have anodized the piece (or at least done something interesting to it!)


This is the electrolysis cell – 12V, -ve connected to the lead and the acid in the beaker


Here it is bubbling away – you can`t see the bubbles on the picture but trust me, is was going!


With 12V running through it it starts to act like a heater and the water rises. This isn`t good because the final stage to “set” or harden the oxide is heating it at the end. We don`t want to heat it now or the layer won`t form properly. I simply sat the cell in a washing bowl of iced cold water to keep the acid cool.


After 45 minutes the aluminum piece was removed. It certainly feels different, it feels smoother and a touch cloudy on the surface maybe. I tried scratching it with a sharp edge and it did not scratch yet the bit unanodised at the top did.


The moment of truth, if I can stain this now and it wouldn`t before than I`ve clearly done something to it and presumably anodized it. This is an organic dye but I believe the cloth dyes you can pick up at Wilkinsons or Hobbyshops are excellent for this:


And then finally dipped into hot water to seal:


Not as blue as yesterday as the dye solution I made up wasn`t as strong but it has definitely taken it and looks really nice in the light. Clearly you don`t have to stain it, the point is it can be done but it also proves that I must have anaodised it to allow the stain to hold:


And then off to make a brew – it is cold outside!!


chris










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Offline Powder Keg

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #1 on: December 17, 2009, 02:03:33 PM »
Thanks for sharing Chris. That looks like fun! I might have to try it.
Wesley P
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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #2 on: December 17, 2009, 02:21:06 PM »
Hi Chris

Very interesting ,,,great job  :thumbup: :clap: :clap: :clap: :clap:,,would a computer power supply work ?  do you think it would be  possible to turn same PS into a variable one ?

Regards Rob

Offline tinkerer

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #3 on: December 17, 2009, 02:25:39 PM »
Wow! Thanks for this, I had no idea that was all there was to anodizing. Do you think a marine 12v battery charger will be good enough for this? Where did you get the acid?

Can't wait to see the pen when finished.
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Offline Brass_Machine

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #4 on: December 17, 2009, 03:16:06 PM »
Hey Chris...

Making this a how to and moving there. I am going to have to give this a try.

Eric
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Offline raynerd

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #5 on: December 17, 2009, 03:24:58 PM »
Thanks guys, you only want to be supplying 12V but letting it draw what it wants upto 4A. I put a multimeter accross it yesterday and at 12V it was drawing about 3.2A.

Sulphuric acid is car battery acid. It is very hard to get hold of as it has many unpleasant uses and I don`t think you can even get it for batteries, it is only sold IN batteries. Can`t help you there - I`m lucky as I work with the stuff most days. It is only 1.5M and if you did it for longer I bet you could get away with 1M so your not looking for a concentrated solution which would be dangerous.

 Rob.Wilson -  Darren started a thread on making a variable power supply. You don`t actually need a variable one for this use. I believe you can convert a power supply to variable.
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Offline raynerd

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #6 on: December 17, 2009, 03:25:51 PM »
lol, you know you`ve "made it" when you get published in the "how to" forum  :ddb:
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Offline andyf

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #7 on: December 17, 2009, 03:48:22 PM »
Quote
Tinkerer asked: Where did you get the acid?

When I did a bit of anodising, I couldn't find any local source of H2SO4 - the car battery places I tried said they didn't carry it nowadays, because batteries are "sealed for life". But one of them kindly gave me a couple of dead batteries taken out of cars. I drained out the acid (with great care, and wear eye protection, just in case) and diluted it down by adding it to the same volume of water (add acid to water, not the other way round). Though impurities were doubtless present, it worked fine for my anodising, using a battery charger. A good battery connected in parallel with the charger to act as a smoothing capacitor may help; I didn't try it. For bigger parts, more current can be helpful. I have sometimes used a 20amp 0 - 30V variable dc power supply, so I could crank up the voltage and hence the amps.

One tip - before anodising, dip the aluminium into a strongish solution of caustic soda (aka lye, aka sodium hydroxide) for 30 seconds. It will fizz merrily, producing a nice satin surface ready for anodising, and will also remove greasy fingerprints. Rinse, then anodise. The caustic soda doesn't appreciably reduce the size of the part.

I tried dyeing, but couldn't get results nearly as good as Craynerd's - nice job  :thumbup:.

Andy

Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline dsquire

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #8 on: December 17, 2009, 04:20:17 PM »
Chris

Very nice set up. This shows that it can be done at home for small items rather simply. I'll bet we start to see a lot more small anodized items show up from a lot of different shops now. Thanks for showing us this Chris.  :ddb: :ddb:  :mmr:

Cheers  :beer:

Don
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Offline Bernd

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #9 on: December 17, 2009, 04:31:14 PM »
I posted this sometime ago.

http://madmodder.net/index.php?topic=1529.0

Bernd
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Rob.Wilson

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #10 on: December 18, 2009, 08:15:23 AM »
Hi Lads

You can get battery acid from ,,, companys who supply TRACTION BATTERYS ,, for use in Forklift truck ,electric vehicals and the likes   comes 1250SG if i remember correct ,,, you will have to by 20ltrs , about £30,to £40, if you live in the NE of UK  ,,,, Battery power ,, washington ,tyne and wear,, will help you out
I will  have to get some more acid as i have used mine for pickeling after silver soldering,,,,,,,,,,,must dig out that PS too and give it ago ,,

Cheers Rob

Offline Andy

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #11 on: December 18, 2009, 10:09:56 AM »
I don't know if this is any good to you, but you can get small quantities of battery acid here - http://www.getgeared.co.uk/Battery_Acid and probably many other places as well.

I got my last lot a couple of years ago from my local car spares place - 1 litre bottles.
From probably the smallest, dampest and most untidy workshop in Bradford, West Yorks, England, if not the world..

Offline NickG

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #12 on: December 18, 2009, 10:22:08 AM »
Thanks for sharing that Chris, very interesting. H2SO4 is also used for pickling copper wjem doing silver soldering.

Nick
Location: County Durham (North East England)

Offline raynerd

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #13 on: December 18, 2009, 02:11:47 PM »
Glad you have managed to source some sulphuric, like I said, I was lucky in that department.

AndyF mentioned dipping into sodium hydroxide solution before anodising which I believe is good practice, I did this on the very first trial version and it fizzed and gave a better surface....infact, my first piece stained better and I wonder if this was the reason? I didn`t do it on my second pictured trial because I didn`t have any keys for the lockup cubboard and I thought it was a good finish anyway but now in retrospect I wonder if it did effect the anodizing? I mean it has definately worked for a fact but my first piece stained even better. Humm, time for a third and final trial!

Chris
 
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Offline andyf

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #14 on: December 18, 2009, 03:16:47 PM »
Chris, as I remember it :scratch: anodising causes microscopic tubules of some Al compound or other to grow all over the surface, so there are tiny pores all over it. The dye gets into the pores. Boiling (or steaming) the part after dyeing causes the compound to hydrate and swell up permanently, sealing the dye into the surface.

"Satinising" the part with caustic soda before anodising must considerably increase its surface area at the microscopic level. So more pores are formed during anodising than on a smooth surface. More pores = more trapped dye and hence a better colour.

That's my theory, anyway  :smart:

Andy
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I've cut the end off it twice, but it's still too short

Offline tinkerer

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #15 on: December 18, 2009, 05:37:37 PM »
I found a good tutorial on anodizing aluminum. It goes along closely to what you fellas are doing, but is a good read.
http://astro.neutral.org/anodise.shtml
Tink

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Offline DMIOM

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Re: Anodising Aluminium
« Reply #16 on: December 20, 2009, 06:40:27 AM »
A few notes & tips on anodising from our experience to get reliable and consistent results

Aluminium naturally oxidises in an oxygen-bearing environment, which is why you rarely see truly-shiny aluminium; the natural oxide though is thin, soft, and disorganised.   Anodising is an electrolytic conversion of the surface of the metal into an oxide, but one in which the oxide forms a hexagonal matrix very much like the cells of a honeycomb. That structure is thicker, more robust and electrically insulating - but the cells have to be sealed after anodising otherwise the porous surface is rapidly contaminated.   Un-dyed (type II) anodising is clear so either you just get the colour of the oxide matrix which is a light grey; or those cells can be loaded with a dye before sealing, which can give a variety of colours through to black (there is no useable white dye for anodising though). The honeycomb does not bend well around corners, so aim for a minimum of 0.5mm radius on any edges.

You can find references to Type II and Type III anodising.  Type II is the most common, and is normally the one to use if you wish to dye the item.  Type III (sometimes referred-to as Mil-Spec or "hard-cote") is a special process carried out with very high current densities and chilled electrolyte; which results in a far smaller pore size which makes it far harder-wearing but the cells are so small they cannot take much dye.

The item to be anodised needs to be 'pure' aluminium - can be various alloys but normally no inserts of other metals. Castings can be a pain to anodise due to imperfect mixes leading to blotchy results. Any welding needs to be with wire of exactly the same composition as the base alloy, otherwise it shows to a greater or lesser degree. If you want a matt surface, either etch it for longer, or blast with glass beads or similar media (never use sand or grit, as it remains embedded and leaves un-anodised spots) or media which has had ferrous contamination.

As it is an electrical process, getting a totally conductive surface and making good connections are key.  The items needs to be grease free - either straight from the machine, or degreased. We use brake cleaner and then dip in a heated degreaser. The test is to check if the item will pass the water-break test - spray the item with water and if it beads up anywhere the surface is contaminated - you need to see a continuous water film with no breaks.

After degreasing, you need to be sure there is no insulating oxide etc. on the surface. If necessary, the item is then dipped in an alkaline strip/etch to get down to bare metal (especially necessary if the item has been anodised before); longer etching can also be used to give a more matter finish.  As almost all aluminium products are alloys, you need to watch for smut on the surface - the strip/etch will remove sufficient aluminium but other constituents such as copper can be left on the surface.  Various alloys will have different levels of smut or soot left on the surface, so the next step which may be needed is a quick dip in a "de-smut".

Between each tank, its essential to avoid carrying-over process chemicals, so a good technique is to hold the item over the tank it has just come out of, spray and/or squirt from a wash-bottle with water (especially threaded/blind holes etc.), dip in a tank or bucket of clean water, spray again and then move to the next stage. You don't normally dry the item between stages.

Talking of water - anodising is a chemical process and all solution make-up and rinsing needs to be with distilled or reverse osmosis / DI water.

The actual anodising can be done to a number of different "recipes". The one we use is one part battery acid ADDED TO three parts water (ALWAYS ADD ACID as otherwise the exothermic reaction will spit acid at you). We then run the tank at 68-70 F (too cold and you will get "winter grey" where the matrix is too small to accept dye properly; too hot and you will get chalky surface from poorly-formed matrix and acid dissolution).  

Racking - you need to suspend the item for all tanks (never let it sit on the bottom) and in the ano tank you need electrical contact as well. The contact needs to be 'agressive' as during the anodising, the aluminium will be trying to grow an insulating layer even beween the workpiece and your contacts. The only three metals you can usually have in the acid electrolyte are aluminium, lead and titantium. You can use aluminium wire but it is renowned for losing contact so the best is Ti - either wire/rod bent into a spring or purpose made clips from the likes of ServiSure.  You will also benefit from aeration/circulation to prevent hydrogen bubbles building up and forming minute insulated under-anodised spots.

Cathode - Lead is often used for the cathode plate (code 4 roofing flashing or similar) and carry the lead up & out of the electrolyte and make connections away from the reach of acid vapour. Aim for at least as much exposed cathode (i.e. not including that against the side of the tank) as the overall area of the the workpiece; and if you can, have the cathode wrap-around the sides/bottom of the tank to get more even results.

Power supply - you can just use a fixed voltage and "let her rip" but for consistent results you are better using a constant-current power supply. You calculate the total wetted surface area of the part (i.e. if its a cylinder, you need to allow for the inside as well as the outside), multiply that by the chosen current density (we use 6 A / sq foot), and set that on your constant current supply.

Duration - if you're using a constant current supply, you can then predict the time needed to achieve your target oxide thickness; light colours need about 0.5 thou; dark colours/black need a full 1 thou. With the method we use, at 6 ASF it takes 120 minutes to grow a full 1 thou or 1 hour to grow 0.5 thou.

Dyeing - you can use clothes dye or food colouring; but for predictable results you are best using proper anodising dyes - these are designed to fit into the anodising matrix and give predictable results.  They can be used cold, but are best used warm (up to maybe 120F) but not too hot, otherwise the matrix is sealed prematurely. Dying can take from a couple of minutes to 15-30 minutes for deepest colouration.

After dying and usual rinse, the item is then hung in the boiling sealant. You can seal in pure boiling DI water (or even just in steam) - that is best for anything which is associated with the food chain or which will be in skin contact (as some folk are nickel-intolerant) - otherwise sealants such as boiling nickel acetate solution provide maximum surface protection.

After removing from the boiling sealant, a good final stage is a quick wipe-down with WD40 to prevent bloom.

PPE at your own discretion - we use boots, battery-apron, gauntlets & face shields; and work in a well-ventilated environment with eye-wash to hand just in case.

You can buy kits - we started with a kit from Caswell and then grew to our current setup (used to anodise housings etc. for our own manufacture of motorsport TV / filming equipment, and for others).

Have fun & stay safe !

Dave

(no connection with ServiSure or Caswell, just users of their products)
« Last Edit: December 20, 2009, 10:43:35 AM by DMIOM »

Offline Bernd

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #17 on: December 20, 2009, 11:52:57 AM »
That's quite a write up there Dave for your first post. Much appreciated for the content.

Welcome to the collective.  :borg:

Would give us an introduction on the introduction page of the forum.  :wave:

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Bernd
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Offline DMIOM

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #18 on: December 20, 2009, 12:44:32 PM »
Thanks Bernd - have watched & learnt from those on here for a while but hadn't posted until now when I thought I might be able to contribute something useful.

Have posted a note the intros as well now

Dave

Offline John Stevenson

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #19 on: December 20, 2009, 12:55:24 PM »
You can get any chemicals you want in the UK from these guys.

http://www.reagent.co.uk/sulphuric-acid-ar/battery-acid.html

2.5 litres for £10

John S.
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Offline andyf

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #20 on: December 20, 2009, 02:30:59 PM »
Dave, I've only just read your post. So good that I've printed it out for future reference.  Concise, too - OK, there was a lot in there, but every word counted. Thanks very much. :thumbup: :thumbup: :thumbup:

Andy
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I've cut the end off it twice, but it's still too short

Offline Jonny

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #21 on: December 20, 2009, 04:45:09 PM »
Havent done any anodising for 4 or 5 years, it was rather hit and miss, even done hard anodising a few times at 13.8v.
What put the dampener on things was my son breaking the 4ft fish tank, gallons of 20% sulphuric flowing out.

I used to get electrical breakdown especially when using wire. Only success was filing up a taper and wedging in a hole.
Tried as many different inks as i could, name it must have tried it some at best with little success, but in the end opted for what the pros use.

Initial current draw on this 4 1/2" dia exceeds 8 amps but drops to around 2 1/2 amps after 10 mins.
http://pic20.picturetrail.com/VOL15/728921/1243489/98753075.jpg
Around 4 amps initial on this dropping to 1 amp.
http://pic20.picturetrail.com/VOL15/728921/1243581/27203664.jpg

Offline DMIOM

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #22 on: December 21, 2009, 07:33:41 AM »
hi Jonny,

agree - connections can be a challenge!

Given that the metals in the tank can normally only be aluminium, lead or titanium; the obvious starting point for many is to keep it all-aluminium.

Some folk try using aluminium bolts and straps, racking etc. but its never that easy/reliable - firstly the mounting hardware has to be stripped (alkaline etch) between runs; secondly aluminium nuts&bolts aren't that great either.  If there is a suitable tapped hole on the workpiece, a threaded rod could be used; or a heavy-gauge aluminium wire doubled-up and 'self-tapped' into the threaded hole. The problem with the latter is (a) getting a good enough contact (needs pounds if not tens of pounds force to get reliable connection) and (b) as the wire doesn't fully fill the hole, its a real trap to carry over process chemicals from one tank to the the next - those chemicals may not be enough to poison the next tank, but if they leak or leach out they can cause visible blemishes on the finished article.

The next step which works well in many cases is to use titanium wire/rod.  If there are any holes or bores in the workpiece (needn't be tapped) then a good springy Ti rod can be perfect to make connection and suspend the item - but it does need to be well-sprung (typically a J shape) - 1/16" rod is too compliant in most cases, but 1/8" rod can work well.  The great benefit of Ti is that it has both the mechanical springiness and that it doesn't need stripping between runs - you run it once to pickle or blue it, thereafter (unlike aluminium racking) it has no significant effect on the anodising current load either.

The 'ultimate' is to use Ti clips - and they have the advantage of presenting a sharp edge to help maintain the electrical connection - two sketches below show round wire and angular clips in use in a bore






After using Ti rods for a while I invested in some racking, clips & hardware from ServiSure, and it was well worth importing them.  We did buy various spines and racks, but for many of the items, we use a spider made of their clips and hung from the tank bar by a 1/8" Ti rod.

Using the full spine etc. for a large item (14" tray)



The clips are available in big sizes as well



Here, a long cylinder (about 9" if I remember correctly) is held using two large clips each suspended from a 1/8" Ti rod to Ti angle



And our most frequently-used combination - a spider of small step-clips on a 1/8" Ti suspension rod



Dave (no connection with ServiSure, just a satisified user)
« Last Edit: December 21, 2009, 08:11:01 AM by DMIOM »

Offline Jonny

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #23 on: December 27, 2009, 07:35:04 PM »
Nice one there Dmiom did have a couple of Ti to try but never got round to it.
Every pro anodiser i have been in uses Ti spring clips and have a Ti machining job to do shortly.

Run out of dye and need to replenish.

I used lead to fully line the rear on both tanks protruding out of the sulphuric level and attaching a meaty croc clip. Aluminium foil rips and tears easilly and starts to float or lift off bottom and sides.

Incidently fitted a fair few of those in your bucket plus made some at work.

Offline cozy

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Re: Anodising Aluminium - my setup that seems to have worked.
« Reply #24 on: April 16, 2010, 08:12:40 PM »
Here's a few pics from when I've done some...

Rear caliper bracket I made for the bike...















Did some other bits as well...