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  • fixturing alloy, working with...

    I'm trying to use 158deg fixturing alloy to:

    Fix a .5mm tungsten needle in a .54mm x 2mm deep hole in a chunk of aluminum,

    To fix the chunk aluminum to the face of a titanium piezeo positioner,

    Fix the positioner to a frame of aluminum.

    yee-ha!

    origionally had planned on glue. I just thought to fixturing alloy because I need to be able to make fine adjustments to the position of the needle, (which could still be accomplished with thermoplastic glue)

    I now own 2lbs of the alloy. I've been experimenting and finding it near impossible to get to stick to any surface.

    I found melting it with a hot air plastic welding gun to be handy.

    any tricks?

    Thanks, Dan

  • #2
    I am not sure what you are trying to accomplish, but Cerro fixturing alloy is not supposed to stick to anything. It is used to "pot" the part being fixtured.
    To hold an odd shaped part for milling for instance, the alloy can be melted and cast into a block, such as a tuna can, the part to be machined would be positioned for the operation and the alloy allowed to cool. Now, the alloy block can be clamped or held in a vise while the operation is performed. When complete, the alloy is melted off.
    Jim H.

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    • #3
      These fixturing alloys expand rather than shrink when they change from liquid to solid. If you position a part in a hole with the liquid metal around it and allow the fixturing alloy to freeze the part will be held due to the compressive stresses in the fixturing metal as it expands against the walls of the hole. Adhesion with the part and/or the container would be undesireable for the normal intended use. If you want to actually bond the pin in the hole you could drill the hole oversize and fill it with lead solder and then drill the right size hole in the solder and also coat the pin with solder and machine off the excess to get a fit. If you then used the low melting point fixturing alloy in the gap you might get some bonding since the fixturing alloy will be somewhat soluble with the solder. If this bonding scheme sounds like a screwy idea I would agree. Use glue if you want it permanently attached.

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      • #4
        Steve Acker has had two articles on Cerro
        Safe uses in HSM/MW, most recently an expansion on its uses in the MW Apr/May '03
        issue. The stuff you are using is 43% bismuth and is designed to be close to neutral volumetrically in going from liquid
        to solid. "It shrinks slightly when it cools and... after about an hour at room temp expands back to almost the exact dimensions of the cavity. Since it contains cadmium,
        care to avoid ingesting the product and particularly its fumes should be taken. You
        can mechanically lock a casting by making some part of the cavity larger than the
        opening. Metallic wetting of the mold cavity by cerrosafe does occasionally happen but not
        often enough to use the alloy as a lowtemp solder. Steve
        Steve

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