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  1. #11
    I am planning to make some moulds using Alumec 89, it's like that 7075 T6 the Yanks rave about but takes a deeper temper, or so I am told.

    Right now I am all theory and no experience. I thought about bead blasting to get that sparked look. I think sand blasting is a no-no on iron because it is the perfect key for rust unless you bead blast afterwards, I find sand blasted iron is rusty before I get it home even on a hot sunny day. I presume you could protect your shut-offs while blasting and cut the gates after maybe?

    OTOH Alumec lasts longer if you anodise which includes a dunk in dilute nitric to remove any extant oxidation before it goes in the sulphuric. Anodising could negate any previous texture. I actually have hopes it might smooth the surface somewhat in those hard to reach spots. Bit worried about whether the ejector pin sleeves are going to fit if I can't block their holes off while it's in the tanks, shellac?

    Regarding someone's earlier comment, I believe the draft angle is supposed to protect the finish on ejection.

    I did buy a die grinding pencil. They are air driven at enormous rpm and come with a 3mm collet. Haven't played with it yet, not really sure what goes in it, the bottle of oil seems to have emptied itself and the instructions have dire warnings about what happens without.
    Whatever, a sparked finish is now passe, the Law of Bling says polish the crap out of it

  2. #12
    Quote Originally Posted by Robin Hewitt View Post
    Anodising could negate any previous texture. I actually have hopes it might smooth the surface somewhat in those hard to reach spots. Bit worried about whether the ejector pin sleeves are going to fit if I can't block their holes off while it's in the tanks, shellac?
    From the anodising I've done I can confirm that you get the same finish after anodising as before. The parts are always slightly smaller - it's hard to say how much but bearings wont have the proper fit after anodising. That's easily solved by pressing some nylon into the bores and the same tactic works well for protecting threads. People block areas of a part off so they can anodise them a different colour to the rest, so it can't be that hard. Probably just need something resistant to sulphuric acid and sodium hydroxide.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  3. #13
    I am told you can recreate a spark eroded texture by sand blasting.


    Now some speculation... a steel cavity might need glass bead blasting as well or rust is instantaneous and you want the cavity side to separate when the mould opens not when the ejectors hit, so don't over key the surface. An Alumec cavity might benefit from anodising if you want it to last but I don't know what that would do to a surface texture. You can frost glass using a mist of hydrofluoric acid, wonder if you could frost an Alumec mould using a spray of caustic soda or frost an anodised mould using a spray of nitric?

    Of course you need a good draft angle to avoid smearing the sides when you open the mould. Minimum of 1.5 degrees for ABS
    Last edited by Robin Hewitt; 24-01-2014 at 11:03 PM.

  4. #14
    [QUOTE=Robin Hewitt;53917]I am told you can recreate a spark eroded texture by sand blasting.
    QUOTE]
    yep theres an injection moulder i spoke to down south who commercially makes angling products rod rests etc and uses this method.
    with the part i had in mind to do, the software i use predicted it would be full of errors as i wanted to use delrin,im told in its usable state it has the consistancy of play doe.
    im working on a drawing for a smaller less demanding part that consists of two parts again delrin i will attempt this regardless of what software says and see what happens plan is to use an airbrush sized kit to lightly texture the mould.

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