Lost PVB Radio Grill

Discussion in 'Lost PLA casting' started by Mach, Oct 7, 2019.

  1. Mach

    Mach Copper

    I'm looking to cast a radio grill like the following using a lost PVB (Polycast) 3D print in aluminum. The problem is the cross section is 1/16" thick. The grill measures 13x8". Short of going hot and fast with the pour is there anything that I can do to improve the changes of success while minimizing porosity? I was originally going to try sand casting (sodium silicate) but I'm guessing investment block will work better. Any thoughts would be appreciated.

    [​IMG]

    [​IMG]

    Grill cross section
    [​IMG]

    Guessing at gating system
    [​IMG]
     
  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Pretty ambitious at those dimensions my friend. Don't think that will happen in sand. I'd say best chance is (significantly) preheated porous block investment, high vacuum, and zinc instead of aluminum. Even in a die cast situation, I think Al is pretty viscous unless you have pressure die cast.

    My 2 cents.

    Best,
    Kelly
     
  3. PatJ

    PatJ Silver Banner Member

    You should gate from the sides, so you have a direct path down the fins.
    The way you have it, the metal will cool trying to run down one fin and fill the others.

    You may also consider knife gates, or semi-knife shaped gates, with are long and thin, along about 3/4 of each side.

    The books generally show a rectangular gate, if you are going to use multiple gates.
    I would use a knife gate on either side though.

    You can also add a small rectangular runner between the part with 5 holes, and the adjacent piece, and then cut that runner out after casting. That would help the 5 hole area fill.

    .
     
    Last edited: Oct 7, 2019
  4. Mach

    Mach Copper

    Thanks Kelly, I'll look into the zinc instead of aluminum and chase the investment block path. I see that BCS has Zamak for sale - I'm assuming that'll work.

    Thanks Pat, I'll redesign with a different orientation, knife gates and internal gating on the interior piece. I went back and looked at the foundry manual. Looks like I'm making rookie mistakes on blending the gates.
     
  5. Jason

    Jason Silver Banner Member

    How was that thing originally made? Was it pressed/stamped?

    I find it funny even with all our "technology" today, recreating stuff from
    80years ago can be a real head scratcher.

    I lean towards vacuum casting in solid block investment. (1/16th of an inch is still going to be damn near impossible with those dimensions) It's going to take a seriously strong suction on the vacuum pump. This is a good question for David. If you lessen the top surface area of a flask, can more "suck" be achieved on the investment to pull the metal further? Think a cone shaped flask with this radio grill laying flat down in the wider part. That with a dozen feeders feeding the part from a main pouring basin at the top.o_O

    Mach, your gating setup won't work if you go block investment. This sketch is really crude, but what I was thinking and easier to post this than arm flailing in cyberspace.

    15705526004271190699334506584540.jpg
     
    Last edited: Oct 8, 2019
  6. Mach

    Mach Copper

    Its not a real radio. Its a prop from a video game, Fallout 4.
    I'm rethinking on the gating but plan to add 1/8" to the back since I can hide it in the radio case.
    I had wanted to try sodium silicate sand and petrobond (like myfordboys video where he makes the extruder mount) but I'm convinced... investment block is the way to go.
     
  7. DavidF

    DavidF Administrator Staff Member Banner Member

    Polycast does not burn out 100% clean, so you need to gate into the bottom of the part and vent the top so it basically flushes the mold out as the metal flows through it. This gating style also reduces the need for vacuum assist.
    I would use zamac alloy instead of aluminum allot due to the thin cross section....
     
  8. Mach

    Mach Copper

    So still working on this. I've doubled the thickness and now have 30 lbs of Zamak to cast. I still want to try sodium silicate after seeing PatJ's mold's in the gas bubble thread. Another time, this is how I'm configuring for investment. Fill from the bottom, and my attempt at knife edge gate. Still need to add the rectangular runner the 5 hole area.

    [​IMG][​IMG]

    Zamak melting point is 735F. With Plasticast burnout schedule, I can pull the investment block at melting point or above temp to ensure longer fill times. Any other suggestions?
     

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