Any reason why I shouldn't get brake cylinders and other parts anodised?

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  • Any reason why I shouldn't get brake cylinders and other parts anodised?
  • In mean engineering reasons, not aesthetic reasons. 😛

    I’m getting a few bits anodised for my Rooster.
    I’d like to get both the master and slave cylinders done.
    The process “grows” the base metal by about half it’s depth. So a 25 micron coating will result in a 0.025mm decrease in the bore size.
    Will that be a problem in itself? I’m guessing that’s within manufacturing tolerance anyway.
    Will the anodising contaminate the brake fluid as it wears any worse than bare aluminium does?

    Seat post, brake adapters, cranks. Any particular problems with anodising these?

    Premier Icon JAG

    All Aluminium brake components (on cars) are ‘hard’ anodised during manufacture anyway. It helps prolong the life of the parts – so it’s already been done 🙂

    Engineering reasons – aye – being an engineer appears to have turned you into a tart. 😀

    b r

    pointless waste of money?

    pointless waste of money?

    The ideal topic for STW then.

    All Aluminium brake components (on cars) are ‘hard’ anodised during manufacture anyway.

    I thought they might be. In which case, does the increased thickness of an extra layer or the die in the colour make any difference?

    Premier Icon Brother_Will

    This reminds me of my bike shop days where the phrase “I’m an engineer was usually the prelude to seeing some inventively ruined bike that needed fixing.

    Well, yes, but, did you ever see a brake cylinder that had been ruined by being anodised? That’s the question.

    Premier Icon NorthCountryBoy

    Hi graham

    would be worth looking at the cylinders are they already anodised or raw alloy?
    If they are raw uncoated then the anodising ads about 0.02mm to the surface if its hard ano finish. I think cosmetic (tarty colors) is thinner.
    This usually has to be accounted for in the design, I am thinking the pistons may be tight with the ano finish after coating.

    Better info here


    The anodising process converts aluminium into aluminium oxide Al2O3. This species has a volume roughly twice that of the aluminium from which it was formed, this gives rise to an approximate growth of half the applied anodic film thickness.

    For example a 50 micron film will use up 25 microns of aluminium in its formation, thus it will create growth of only 25 microns per face.

    An internal diameter will decrease by 50 microns if such a film is applied, an external diameter will increase by the same amount.

    This must be borne in mind when making allowances for growth:

    Remember-growth is approximately equal to half the applied film thickness per face*

    A special case that needs discussion is that of growth on threads:

    Although the film grows on threads in exactly the same way as it does on anything else, the thread angle causes an effective growth, which means that a greater allowance needs to be made for threads.

    The effective growth on diameter can be calculated by the following formula:

    Premier Icon takisawa2

    I had an issue where some already anodised parts were stripped by etching back to raw alloy, then re-anodised. The bearings weren’t such a snug fit afterwards.

    NorthCountryBoy, it looks like you copied that from 😉
    That’s the place I was going to use as I cycle past there on my way to work.
    Does 25 microns or 0.025mm matter on a brake cylinder? I’ve seen brake and clutch cylinders on cars and trucks with about 0.5mm wear before they failed, but I don’t know what the undersize limit is before the piston binds.
    It’s Hope Mini Mono brakes if that makes a difference.


    Can’t you tape off and block any holes so the inners don’t get anno’d? Although might prove difficult to get the connections to the part current wise..

    Reading about the process, it sounds like any plugs or masking would have to be acid proof.
    I’m sure they can advise me on what they can do, but as they say, it’s usually cheaper to anodise an item completely than to mask off areas, so it would be nice to know that someone else has already done it and the pistons still slide in the bores.

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