Discussion in 'UK DIY' started by David Lang, Jun 9, 2005.

  1. David Lang

    David Lang Guest


    Two questions about aluminium sheet approx 1mm thick.

    Can I cut it using my table saw with a TCT blade and/or will doing so blunt
    the blade rapidly?

    Can I get a polishing mop to fit a 115mm angle grinder, so I can mirror
    finish it?

    David Lang, Jun 9, 2005
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  2. David Lang

    Roger R Guest

    I thought paraffin was the fluid for working aluminium?

    Roger R, Jun 10, 2005
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  3. David Lang

    David Lang Guest

    Hi Chris
    Thanks - I'll watch those points - I have enough wobbly edges as it is!
    I was trying to avoid the 'by hand' method. I saw on The Caravan Show the
    other night someone mirror finishing aluminium with what looked like an
    angle grinder, but the pad was at right angles, The pad appeared to be
    discs of cloth stitched together.

    David Lang, Jun 10, 2005
  4. David Lang

    Andy Dingley Guest

    I really wouldn't do this - there's a kickback risk. If you get the
    right sort of sawblade (negative tooth rake) then it's easy and safe.
    You won't "blunt the blade".

    It will be incredibly noisy though, especially on a saw that's less than
    perfectly rigid!

    You'll also want something like a Dreadnought file (a coarse-toothed
    curved tooth rasp) for working the edges. Aluminium benefits from new,
    sharp coarse files and rubbing the teeth with chalk before beginning.
    The teeth tend to "pin up" with aluminium, so the rasp stays cleaner.
    No, the angle grinder is much too fast.

    There are useful nylon bristled abrasive-loaded rotary brushes you can
    get to use in a hand drill. These are excellent for copper, but
    aluminium is just a bit too soft - you can too easy put obvious swirl
    marks in with them.

    I suggest a range of hand Garryflex blocks instead (also made for
    Roebuck), rubber blocks full of abrasive grit in a range of grades.
    Aluminium is soft enough that doing it by hand doesn't take long, even
    for large pieces. Make sure you use the coarsest first and don't go
    finer until you've got the last of the scratches out. A mirror finish is
    easy and only takes moments, a good unscratched mirror finish takes more
    care and effort.

    Either keep separate sets of blocks for ferrous and non-ferrous metals,
    or rub then clean when swapping over - otherwise you get black smears.

    Look after your aluminium when you're working on it (masking tape etc.
    do avoid scratching where you're working). It's easier to not put big
    scratches on than to take them off later. Emery or wire wool will shift
    them, if you have to.
    Andy Dingley, Jun 10, 2005
  5. Easier to get an accurate cut with decent tinsnips? Or if well supported a
    jigsaw with suitable blade?

    I'd be very worried about a table saw 'grabbing' and throwing things every
    which way.
    Most polishers run at a low speed to avoid burning the polisher and paste.

    I'd try a random orbit sander with a lambs wool bonnet.
    Dave Plowman (News), Jun 10, 2005
  6. David Lang

    Rob Morley Guest

    Grinders run much too fast for polishing.
    Rob Morley, Jun 10, 2005
  7. read this a while back and thought it was interesting,20967,693558,00.html

    "when aluminum rusts, it forms aluminum oxide, an entirely different
    animal. In crystal form, aluminum oxide is called corundum, sapphire or ruby
    (depending on the color), and it is among the hardest substances known. If
    you wanted to design a strong, scratchproof coating to put on a metal, few
    things other than diamond would be better than aluminum oxide."

    So you are really going to be polishing the oxide or corundum, the trick is
    not to do anything that will cut/scratch through the coating I guess

    Paul \( Skiing8 \), Jun 10, 2005
  8. David Lang

    Huge Guest

    You can't.

    The moment the metal is exposed to the air, it forms a coat of oxide.
    Huge, Jun 10, 2005
  9. David Lang

    Parish Guest

    Solvol Autosol is the stuff for polishing aluminium used with a 3" felt
    wheel (Black and Decker make one) that fits your leccy drill using the
    same arbour as a grinding wheel. You may need to finish with a bit of
    Solvol Autosol on a cloth to remove any polishing marks but it is easy.

    Used to get a chrome-like finish on engine castings when I was a biker.

    Parish, Jun 10, 2005
  10. David Lang

    Huge Guest

    Sure. Whatever you like.
    You're looking at a coat of aluminium oxide. The fact that it's a nice
    optically flat one due to the metal beneath being flat also is irrelevant. It
    is simply impossible to have a bare coat of aluminium metal in air.
    Huge, Jun 10, 2005
  11. Aluminium oxide is transparent -- clear as glass.
    It's also incredibly hard (not far off diamonds), although
    the layer which forms is really too thin to provide much
    protection. It can be deliberately thickened by anodising,
    which makes the surface harder. It's a damn good electrical
    insulator too, which is a bad thing when trying to connect
    aluminium conductors.
    Andrew Gabriel, Jun 10, 2005
  12. David Lang

    Huge Guest

    Crumbs, someone's paying attention.
    It protects against the oxygen in the air, which is what counts.
    Huge, Jun 10, 2005
  13. David Lang

    Andy Dingley Guest

    Autosol is a chrome polish, so it's a very hard abrasive. It'll work on
    aluminium, but it's a lot more effort than you need. Using a coarser and
    softer polish will get you there much more quickly.

    Don't use Brasso. Unless you clean it carefully afterwards, you can get
    discolouring, because of the ammonia in it.
    Andy Dingley, Jun 10, 2005
  14. David Lang

    Andy Dingley Guest

    Not in practical terms. Aluminium takes hours or days to form an
    appreciable oxide coat, and even then it's pretty negligible. Ti in
    contrast is far more reactive and you can watch the oxide film form in
    seconds. If your aluminium has an oxide coat that you can mechanically
    notice, it got there by anodising, either deliberately or as a
    side-effect of heat treatment or pickling.

    And "aluminium oxide" covers a range of materials, where the mechanics
    depend on the crystallography, not just the chemistry. Comparing the
    stuff found on a sheet of aluminium metal to corundum is ridiculous.
    And it will never be "ruby" or "sapphire" unless you start doping it.
    Andy Dingley, Jun 10, 2005
  15. David Lang

    Grunff Guest

    While it will work on aluminium (as long as you wash it afterwards to
    avoid discolouration), it is not in any way a good polish for perspex -
    it will leave a very cloudy surface. Try it.
    Grunff, Jun 10, 2005
  16. David Lang

    Mary Fisher Guest

    Oh - is THAT what does it! I should have realised ... Brasso is certainly
    not effective in polishing Al but I don't know what is in a
    household/workshop situation.

    Mary Fisher, Jun 10, 2005
  17. David Lang

    Huge Guest

    Damn. My 'A' level chemistry master was lying. I wonder why?
    Huge, Jun 10, 2005
  18. Eh? Have they changed the formulation? It certainly used to work ok.
    Dave Plowman (News), Jun 10, 2005
  19. David Lang

    Andy Dingley Guest

    Brasso is a soft tripoli in a liquid medium. Tripoli is an appropriate
    polishing medium for soft metals like aluminium and is pretty good for
    some harder plastics too. It won't make a dent in chrome though, hence
    the existence of Solvol Autosol. However the choice of liquid for Brasso
    is chosen for cuprous metals, and it's not a good choice for aluminium
    of plastics.

    In particular, it's hard to polish plastics with a liquid medium and a
    standard mop. You're much better off with a paste medium. A hard mop is
    too likely to burn the surface on plastics, unless you arrange a lapping
    As you know everything about everything, perhaps you'd like to explain
    to us _why_ Brasso uses ammonia, and why this is an irrelevance (and
    potentially a harmfully discolouring one) for aluminium.
    Andy Dingley, Jun 10, 2005
  20. Actually about a day after you polish it, a new oxide layer forms. Its a
    bit of a watse of time really.
    The Natural Philosopher, Jun 10, 2005
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