Foo G

Jig & Spinnerbait Mold Design questions

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I've been working on some jig and spinnerbait designs for a while with the intention of having some aluminum molds cut. However, I don't have a lot of knowledge about pouring lead. My biggest mold design concerns are in the areas of venting, sprue size, and gate size. I understand that the cavity size and geometry, pour temp, mold temperature, pour rate, etc. will all play a big part in it, so I'm really looking for some generalities. What works for you or what are the characteristics of your more successful molds? I'm basically looking for input on the following:

  • Vent depth -- What depth will allow for air to escape but still shut off without allowing molten lead seep in?
  • Gate shape -- Is a rectangular gate better or worse when pouring? I assume it would be better when it comes time to trim the runner after the baits cool, but I don't know if it will equate to fill problems or not.
  • Gate size (area) -- Ideally I'd like to minimize this without creating fill problems. What gate dimensions (width x depth for rectangular, diameter for round) do you need for 1/4, 3/8, 1/2, 3/4, and 1 oz. baits? Do I need different gate sizes for different bait sizes or is it usually a 1-size-fit-all thing?
  • Sprue size -- In plastic injection molding, the sprue size is usually around two times the size of the gate. Does the same ratio hold true for molding lead?
  • Weedguard core pin diameter (for glued-in weedguards) -- How oversized should the core (base hole) pins be for the weedguard hole? In other words, how much will the hole shrink after the bait cools?

Thanks for your help and input!

(I also posted this thread in the Lure Making / Wire Baits section because I wasn't sure which category would yield the best or larger audience. I apologize to those who may be a little annoyed at seeing it twice.)

Edited by Foo G

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