Shielding

DIY lead brick

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:

• 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

• 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

• 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

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

• 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

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

• 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

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

• 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