Making weights with plaster molds????
24 replies to this topic
Posted 05 January 2009 - 02:12 PM
Glad to help and good luck.
Let us know how you make out.
Posted 05 January 2009 - 11:16 PM
I would add additional mold on the bottom of the mold to better anchor the rod in place... That should keep the rod in the center a little better.
Posted 09 January 2009 - 12:58 AM
Shouldn't this post be in the wire bait section, the place were the real men post !!
I've done a bit of R&D (rippoff and duplicate) of a related lure, the Zzinger.
This mold was my first Bondo mold and was made in 1988. It's 20 years old and has poured over 50 castings. (Ignore the 2 holes that I drilled in the back of the casting, it was a balancing experiment)
Luckily I saved a private message about how I make my Bondo molds. I hate re-typing stuff
First you need a pattern, or master that you're going to copy. It can be
made from metal, wood, plastic, etc., but it must be fairly strong and
rigid, have a smooth surface, and have no undercuts, so that it and the lead
casting will come out of the mold. You could also copy an existing
lure as well.
Here’s a pic of a wooden, balsa, pattern:
Here's a pic of the resulting mold:
I start by making two solid Bondo blocks, the spinnerbait shown above used
pieces the size of a cigarette pack. I put the spinnerbait pattern on top of
the block and try to position it for a best fit, and I leave room for the
pouring sprue. I trace the outline of the bait onto the bondo block with a
pen/pencil. I then cut a rough pocket into the block following the trace
lines. I use a Dremel with a rotary burr to cut the pocket, but a chisel or
an endmill in a drillpress works too. The pocket must be a little bigger
around than the pattern and slightly deeper than 1/2 the thickness of the
pattern. I do the same with the other block: note that it will be a mirror
image, or "other hand". When both pockets are cut out, the pattern will fit
inside loosly when the blocks are closed around it. I now have a rough mold.
The pattern is now 'waxed' so it won't stick to the bondo, I use Arrow floor
wax; grease and oil could work too as a release agent. Rub the wax all over
the pattern with an old toothbrush, the wax coating must be thorough but
thin enough not to see.
Now mix up about 3 tablespoons of Bondo+hardener and spread it into one of the
pockets you cut in the blocks. Put the pattern into the still soft Bondo and
wait for it to begin hardening. Get a knife or single edge razor blade
ready. When you pressed the pattern into the Bondo, the Bondo will bulge out
and trap the pattern. You have to cut away the bondo that oozed out and
around the pattern. The bondo starts to harden in 1 to 15 min, depending on
the temp. and the amount of hardener. Start trimming as soon as the bondo
starts to firm up, don't let it get too hard because it will get too hard to
cut. Trim the bondo down to the face of the block, which should be the
midline of the lure. If all went well, you should be able to pry and wiggle
the pattern out of the first block of Bondo after about 20 minutes . The freshly hardened Bondo is a bit sticky, so I'll take it to the sink and run hot water and a bit of soap over it while removing the pattern. If the pattern won't come out, try trimming a bit more
bondo from around the the pattern.
I now cut shallow holes or dimples on the mold face with a drill bit, these
will form and mate with the 'pins' on the other mold half.
To make the second half of the mold: put the pattern back into the first
block and wax the whole mold face, sides, pattern, and the holes/dimples.
Mix up a couple of spoonfuls of bondo+hardener and fill the rough pocket of the
second block of Bondo and put a bit on its face as well. Put the second
block on top of the first block and gently squeeze them together. There
should be excess Bondo oozing out between the two halves, the second half of
the mold including the index pins will form and mate with the first half.
Make sure that the two halves line up with themselves and are 'square' to
each other while the Bondo hardens. I put some lead ingots on top to keep
them pressed together during the hardening.
You can trim the excess oozed out Bondo from the sides after it's hardened a
You can pry the mold apart after about 20 min, I do it under hot running
To cut the sprue, put the mold together (leave it empty, i.e. no pattern
inside), and slowly drill a 1/16" hole along the mold parting line. Check
your progress every 1/8" to make sure the hole is being cut equally on both
sides of the mold. Be careful as it breaks through into the finished mold
cavity, you don't want to gouge the insides. Enlarge the hole with a 1/8"
bit and then use a countersink bit (or a big drill bit) to cut the funnel
The next day it should be hard and cured enough and ready to use. I coat the
cavity and sprue with 'Rapine Mold Prep', but coating with candle smoke/soot
or burnishing the cavity with a soft lead pencil will also help to prevent
wrinkles and other casting problems. Some molds don't work well at first,
but after a bit of use they sometimes improve. I do get flash and fins from
most of my bondo molds, but squeezing the mold together harder just seems to
trap air and makes worse castings.
I've read that plaster of Paris does NOT work well with lead due to a chemical reaction between the two.
Hope that helps!
Posted 09 January 2009 - 02:30 AM
The mold-gating design provided by Vodkaman is unquestionably the best one for your purposes. The only alteration would be that the vents at the #2 location are unnecessary, as the rod pass-through holes provide enough venting at that area. With that one sketch, Vodkaman has given you most of what you need to know. Glaucus's mold follows this pattern, and his advice is also instructive here.
I recently made a Bondo mold (3oz cavity) similar to your proposed buzzbomb design. After quite literally several hundred casts, it's as good as new. I used wheel-weight (hard) lead with no problems.
Some concens that will confront you:
Do not apply oil or any liquid to the cavity, or to the line-hole rod. Oil will cause bubbles in the casting and is a potential fire and splatter-hazard.
Use hard stainless wire of at least 0.050" diam for the rod. Replace whatever line-hole wire you used during mold construction with the 0.050" (or larger) rod. Carefully shave or drill out the rod pass-through holes to accomodate the 0.050" rod.
As the lead cools, expect the casting to grip the wire very tightly. The rod must be smoked or dusted with either mica powder or moly powder before each pour. Removing the fragile casting from the wire or rod may be-- by far-- your biggest challenge. Removing the wire before opening the mold may be the only way to avoid damaging the casting. Do not ignore this consideration.
A sprue located on one of the buzzbomb 'wing' provides the best placement, and be sure to make each mold half no less than 1" thick.
Bondo is an insulating material with poor thermal conductivity. This means that only a small sprue is necesary. You should get perfect results from a sprue that tapers to an 1/8" or less. I used 1/8" with no difficulties, and probably could have gone as small as 1/16"-- no exaggeration.
Hope this helps, good luck.
Posted 10 January 2009 - 04:13 AM
Thanks very much guys for the added info. Nuch appreciated indeed!
Glaucus how do these zzinger lures work in the water compared to Buzz-bombs? They look good and you mold and info attached looks fantastic!