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  1. #1
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    Default Cast alluminium surface finish

    Is it easily possible to get a smooth surface finish when casting aluminium?
    Is it as simple as using fine sand. I need to make sinker mould and want the finish of the lead to be reasonable smooth.

  2. #2
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    It's basically the sand. For a fine finish you may even have to got to plaster (but well dried). Another alternative might be a split Al mould, similar to that used for blackpowder shot/ bullets.

    Michael

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    Quote Originally Posted by Michael G View Post
    It's basically the sand. For a fine finish you may even have to got to plaster (but well dried). Another alternative might be a split Al mould, similar to that used for blackpowder shot/ bullets.

    Michael
    ..should have clarrified that I need to make the alloy mould so that I can cast the sinkers.


    So is pouring ally on plaster safe?.?

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    When they cleaned out the water jet cutter tank at work I took some of the fine, used garnet home and dried it out, I haven't cast anything with it yet but you can imagine how fine it is after going through the water jet, I'm not sure if the % of metallic particles will have any affect on the casting, they may impregnate the outer layer but I doubt that will matter for me. got any shops with a water jet near you?

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    A couple of years ago I was in QLD and my mate's mate was using some form of silicone to cast lead sinkers

  6. #6
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    How smooth do sinkers need to be If you want high finish like bullet moulds they are machined in Aluminium on a mill, sand finish would be Petrabond for a really fine finish you could use Delft Clay but that is pricey ( and hard to get at the moment). Mt mate uses a Douglass type setter I don't know ho he makes his moulds I can ask him after the 11th when he comes back to civilisation.

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    Quote Originally Posted by eskimo View Post
    ..should have clarrified that I need to make the alloy mould so that I can cast the sinkers.


    So is pouring ally on plaster safe?.?
    The plaster needs to be well dried so that there is no water to flash to steam. Probably some time in the kitchen oven would do it.

    What shape are the sinkers? It may be just as easy to machine a cavity directly into the Al block. I'm off until the 11th, so could help if needed.

    Michael

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    Quote Originally Posted by Michael G View Post
    The plaster needs to be well dried so that there is no water to flash to steam. Probably some time in the kitchen oven would do it.

    What shape are the sinkers? It may be just as easy to machine a cavity directly into the Al block. I'm off until the 11th, so could help if needed.

    Michael
    sinker shape is akin to a bullet eg 20mm round with a flat bottom then about 1/2 along tapers to a point...or small length round bar with a solid cone on one end
    20201229_114201[1].jpg

    20201229_115545[1].jpg

    the round solids fit into the mould to adjust weight. My intention is to make the moulds so that spaces are not needed.

  9. #9
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    I have a 60 degree included angle countersink that is 19.5mm in diameter. I think you would want to pour into the base of the sinker rather than the top (potential to freeze off too quickly), so an open top mould would probably do it. Have a think, let me know...

    Michael

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    Quote Originally Posted by Michael G View Post
    I have a 60 degree included angle countersink that is 19.5mm in diameter. I think you would want to pour into the base of the sinker rather than the top (potential to freeze off too quickly), so an open top mould would probably do it. Have a think, let me know...

    Michael
    you cant cut that with a countersink end mill...can you????? Obviously, I have no idea...lol.

    If the bottom is open what is going to hold the wire in the centre.
    Maybe I need to come and see you before you go back to work.

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    Quote Originally Posted by China View Post
    How smooth do sinkers need to be If you want high finish like bullet moulds they are machined in Aluminium on a mill, sand finish would be Petrabond for a really fine finish you could use Delft Clay but that is pricey ( and hard to get at the moment). Mt mate uses a Douglass type setter I don't know ho he makes his moulds I can ask him after the 11th when he comes back to civilisation.
    Smmothness is not a problem normally...but when surf fishing the flow in the gutters and together with weed etc things get in a mess easily...dont want rough casting cutting or a brading the line. I have a few molds and finish is generally quite smooth.

  12. #12
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    Quote Originally Posted by eskimo View Post
    you cant cut that with a countersink end mill...can you????? Obviously, I have no idea...lol.

    If the bottom is open what is going to hold the wire in the centre.
    Maybe I need to come and see you before you go back to work.
    I was thinking something like this -
    Sinker.jpg
    The countersink would not mill the material out as such. I'd drill most of it out and use the countersink just to clean up. The wire would go in when the mould halves were fastened together. There might be a little bit of leakage around the wire but if the mould was resting on a sand tray, it would not be much. For wire, I'd just use a bit of stainless welding wire twisted up (I have 0.9 or 1.6 if the fish are really big...). The sketch is a bit dodgy - there should be less distance between the bottom of the mould and the bottom of the cavity.
    It could be moulded the other way up but the mould gets more complicated with how to get the metal in and the part out. This way you can make the body a little longer and clean up the base in the lathe if needed.

    Michael

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    Quote Originally Posted by Michael G View Post
    I was thinking something like this -
    Sinker.jpg
    The countersink would not mill the material out as such. I'd drill most of it out and use the countersink just to clean up. The wire would go in when the mould halves were fastened together. There might be a little bit of leakage around the wire but if the mould was resting on a sand tray, it would not be much. For wire, I'd just use a bit of stainless welding wire twisted up (I have 0.9 or 1.6 if the fish are really big...). The sketch is a bit dodgy - there should be less distance between the bottom of the mould and the bottom of the cavity.
    It could be moulded the other way up but the mould gets more complicated with how to get the metal in and the part out. This way you can make the body a little longer and clean up the base in the lathe if needed.

    Michael
    if you look closely at one of the pics I posted you will see a metal thread (spot welded to wire) which allows for a plastic tip to be screwed onto the base of sinker....this of course must be cetrally located.

    this pic should explain
    20201223_170539[1].jpg

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