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Re: Matt's Spincasting Project (even longer)

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  • Alan J
    Hi, I worked for GW US a few years ago and my first year there was as a mold cutter in the casting department. I m not an expert, but I still did do both
    Message 1 of 4 , Jun 1, 2004
      Hi, I worked for GW US a few years ago and my first year there was
      as a mold cutter in the casting department. I'm not an expert, but
      I still did do both casting and mold cutting while there so will
      share what knowledge I have.

      "cerberus_studio" <artbeau@a...> wrote:
      > Hi Everyone:
      >
      > 1) The unit does not have a variable speed control; it only spins
      at
      > one speed while turned on. It seems pretty fast to me, but I have
      no
      > idea how many RPMs it goes.

      As you don't know the speed I'm going to make the assumption it's
      fairly high, that way my advice may be more than you need not less.

      >Will it generate enough force to cast
      > pewter figures?

      Gravity alone is enough to cast a mini, so any additional force will
      just help to achieve better casting results (well there is a point
      where too much speed verses not enough pressure can lead to the
      molten metal going right through the mold, but we'll get to that
      later)

      > What is the relationship between speed and casting?

      The centrifugal force exerted by the act of spinning a mold will
      force metal from the center of the mold (the pour hole in the top
      center of most round rubber production molds) to the outside edge.
      Once the proper gates, channels, feeds and vents have been cut into
      a mold the metal is able to get from the pour hold to the cavity
      left by the figure during the vulcanizing process (this is sometimes
      referred to as "pressing in" a model/mini as the two rubber discs
      are both heated and placed under high pressure squishing
      or "pressing" the mini into the surface of the mold).

      The higher the speed, the greater the force; the greater the force
      the lower the temperature you need to keep the metal at to active
      quality casting. This could be important if you have concerns about
      the longevity of a production mold but would be a little less of a
      concern if you're just doing this at the hobby/classroom level. Of
      course you will need to experiment to find the "optimum" balance of
      speed and temperature that works best for you. Too low a
      temperature and the metal will cool before it casts and you'll end
      up with soft detail or half filled cavities, too hot and you bake
      the mold; too slow/too fast will give you problems with filling as
      well (like it won't or the metal goes through the mold- but I'd
      doubt you have to really worry about that last one unless your
      machine is really fast).

      > Will there ever be a need for it to move at slower speeds? Should
      I
      > attach a variable speed controller to adjust to a slower speed?

      Maybe; it really depends on how fast the thing is to start with. If
      it's slow to moderately slow you probably won't need to worry about
      it, if it's fast to very fast you may need to slow it down a bit.

      > 2) I removed both of the internal arms to reveal a 3/8" threaded
      > shaft.I am going to attach a 14" diameter aluminum potter's wheel
      > head to create a flat, circular surface to place the mold upon.
      Do
      > you think this will be a sturdy base for my molds?

      Not being familiar with aluminum pottery wheels, I'm going you give
      you a guarded "should be fine" but caution you to use your common
      sense and keep your mind on safety. How thick is the wheel?

      > 3) I know that molds must be clamped to distribute even pressure
      to
      > prevent flashing. I was experimenting with the concept of securing
      a
      > large 25lb body builder weight on top of the mold, but my dad (the
      > engineer) suggested clamping a round, plywood disk clamped on top
      of
      > the mold to apply even pressure. Any ideas about the best
      material
      > to clamp on top of the mold?

      I'd suggest you use a second potter's wheel- wood can shatter under
      pressure and speed. This may not be necessary, but not knowing your
      setup, I know metal will be safer.

      > 4) The top plate will need to be clamped in place, so we thought
      that
      > we should permanently affix 4 threaded rods to the wheel-head and
      > drill corresponding holes in the wood disk. The wood would then
      be
      > clamped in place with wing-nuts. Is this a good idea? Any other
      > suggestions for securing hardware?

      I've seen this (or something very similar anyway) on a spin caster
      that Alumilite sold on their site a few years back, so I'd think
      it'd be fine.

      > Also, should we have 3 or 4
      > posts attached to the wheelhead?

      Three to triangulate the pressure seems reasonable… someone else may
      have a better answer here.

      > 5) I looked on EBay for electric melting pots for bullet pouring.
      I
      > called one of the manufacturers and they told me that the pots
      reach
      > a peak temperature of 900 Fahrenheit and should be lined with a
      > stainless steel pot to prevent corrosion. I think it'd work well
      for
      > melting pewter—what do you think? How large of a ladle should I
      get
      > for pouring metal?

      I have one, it works fine. Can't say about the ladle- it'll depend
      on the size of the melting pot opening and how much metal you need
      to fill the mould and I can't be sure of ether. Medium, maybe…

      > 6) Finally, some questions about the casting process itself: Do
      you
      > pour the metal and then spin the mold or should the mold be
      spinning
      > before you pour the metal?

      Steps:
      Heat metal
      Talc mold
      Secure mold in machine
      Spin mold
      Pour metal
      Let mold spin for a moment longer (5 or so seconds)
      Remove mold and wait about twenty seconds
      "Pop" the mold- This is slang that was used when I worked for GW ten
      years ago, so may not even be current, but it means to sort of flip
      the edge of mold to separate the halves to release some of the
      heat. The casters did this after they spun all the molds on their
      table, usually fifteen or so, but twenty seconds to a minute should
      be fine. The only problem with popping too soon is if part of a mini
      is still too soft you'll ether get some warping or in rare cases
      you'll get a small pool where part of the mini should have been. The
      longer you wait the more wear to your mold in the form of heat
      damage.
      Let cool for another 30 seconds to a minute and break the minis off
      the sprue. The wait here is just so they cool enough to comfortably
      handle them with heat resistant gloves.

      > Any difference in technique for pouring a
      > mold with a lot of small figures (3/4" to 1") versus pouring a
      mold
      > with a few larger figs (1.5" to 2")?

      Not that much, you may need to scoop a little more or less metal but
      until to start getting to the larger parts that make up dragons and
      monsters you won't really need to worry about it a ton. Until you
      get used to it just scoop half a ladle at first see how that works
      and adjust from there.

      > Thanks in advance for all of your assistance. I'll keep you all
      > updated about my progress.

      Hope this helps and good luck!
    • cerberus_studio
      Hi Alan: A few people e-mailed me off list, but your answers have been the most useful so far. Thanks for taking time to reply to my long post! Sincerely,
      Message 2 of 4 , Jun 1, 2004
        Hi Alan:

        A few people e-mailed me off list, but your answers have been
        the most useful so far. Thanks for taking time to reply to my long
        post!

        Sincerely,
        Matt
      • Alan J
        ... long ... No problem, if you need anything else feel free to ask. Alan J
        Message 3 of 4 , Jun 1, 2004
          "cerberus_studio" <artbeau@a...> wrote:
          > Hi Alan:
          >
          > A few people e-mailed me off list, but your answers have been
          > the most useful so far. Thanks for taking time to reply to my
          long
          > post!
          >
          > Sincerely,
          > Matt

          No problem, if you need anything else feel free to ask.

          Alan J
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