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DIY lead brick

castle.jpg

My bricks are 6 x 2.5 x 1. IIRC they were supposed to be 6 x 3 x 1 but I didn't have big enough material on hand.

I made the molds on my Sherline 2000 CNC out of 1/8“ steel slats. Bug me if you really want details, but basically I'm most likely to add details if I design new mold(s) for the actual desired brick size.

Currently takes me about 30-45 minutes a brick. Secondary mold(s) would speed this up considerably. IIRC I have material to make 4

JM setup using:

  • Steel brick mold (custom)
  • Lee Precision 20 Pound Pro 4 Electric Metal Melter
  • Scrap lead from eBay
  • Quench tray

Procedure:

level.jpg

  • Fill lead pot about 75%
    • As needed, skim surface
  • Assemble brick mold
    • Run mold surfaces against steel cart to quickly clean them
    • Run a slat through mold crevices to quickly clean those
    • Place slats into bottom
    • Fit top onto bottom assembly
    • Verify fits together decently well (observing slats at at right angles)
    • Pound the mold against a flat, hard surface. Flip over and pound the other side
    • Place strap around mold and tighten

in_pot.jpg

  • Pre-heat / fill mold
    • Place brick mold *into* the lead pot
      • Since it was partially filled it should fit
    • Initially the mold will float
    • As lead fills the mold (due to sealing imperfections), adjust it as necessary to make sure it sinks to the bottom
    • Should take 5-10 minutes
    • If it doesn't fill, don't worry about it
  • Remove mold from pot and place underneath pot at a slight angle (sprue up)
  • Open lead pot. Wedge a screwdriver at top so that it stays open
  • Once mold begins to overflow, remove screwdriver

in_pool.jpg

  • Final filling
    • Knock off all excess lead every 5-10 seconds
    • After knocking of, observe suction into sprue. If there is no more suction / solidified, you are done
    • Add a small pool to the top
    • If necessary, use a water squirt bottle to stop lead leaking out the back of the mold
      • This will contaminate some of the lead with water, making it dangerous to throw back in
      • Place all overflow into a bin to dry
    • Do a final knockoff to make the sprue easier to remove

quench.jpg

  • Place mold into shallow water
    • No higher than the bottom plate
  • Let cool for 10 minutes
  • Remove from water onto table

sprue_clean.jpg

  • If necessary, scrape off sprue excess
  • Loosen clamp and slide off
  • Gently tap the a side outward. Rotate through the 4 left / right + top / bottom combinations until both top and bottom are loosened

open_top.jpg

  • Remove top mold
    • Sprue should give some resistance but pull out fairly easily

empty.jpg

  • Tap brick in mold against soft metal (ie aluminum) to release brick. Ensure sprue is overhanging an edge such that you aren't pounding it into the mold
  • Inspect brick
    • If there is a large sag at the top you cooled the brick too quickly (before quenching)
    • If brick is damaged around sprue, you didn't let it cool long enough
    • If the lead is not one solid piece and/or only half filled, you did not sufficiently pre-heat the mold
  • Use sheet metal cutter to remove sprue
  • Use a hobby knife to debur brick edges

General notes

  • I usually pickup the mold by either the clamp screw or by grabbing an end (using grove joint pliers)
  • I've experimented with only removing the top to reduce mold cleaning
  • Full brick quenching will release lead easier but may warp mold and other issues

scale.jpg

  • Unclear if should keep/remove antimony (adds hardness)

waste.jpg

  • If excess lead may have been contaminated with water, let it dry before reusing

Mold

https://github.com/JohnDMcMaster/uvscada/tree/master/ngc/pb_brick

Crude g-code generator. Think the mold may also be off by 1/8” or something like that

shielding.txt · Last modified: 2016/10/17 15:52 by mcmaster