Monday, February 18, 2013

Making a Two Part Mold for Casting


Posted: 21 January 2012 10:38 AM   [ Ignore ]
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As promised, I am going to show you one way I make molds.  There are so many different ways to make molds, but generally the principal remains the same.  Mostly it is the choice of materials that constantly changes depending on what your master is fabricated from.  Sometimes a master mold will need to be flexible.  Other times it needs to be rigid or semi flexible.
When I first go to make a mold of an object, the first thing I have to consider is the general plane orientation of the sculpted piece.  For example, if I have a humanoid with protruding limbs,  I would divide the piece into separate planes.  Usually this means molding the body in pieces;  having a leg that is bent from the primary body plane cast separate, or weapons, or arms…etc.  Sometimes this means your figure will be cast in as many as 4 - 5 pieces.  Don’t worry about how many pieces you need to cast, because multiple pieces does not really add any time to the final casting production process;  since everything is usually cast in one shot using the same pour.
The next thing I have to consider is what my master is fabricated from.  Can the master be heated or does it have to remain cool to prevent it from melting?  Is the master soft or rigid?  Will the master dissolve in water or oils?  As I said above, the principals of molding remain the same, but the materials used to do it will change depending on how you answer these questions.  Sometimes I make molds that are rigid on both sides and are made from the same material that is being poured into them to make a cast!  Many times I make molds that are rigid on one side and flexible on the other.  It all depends on how your master is shaped, what it is made of, what you want your finished product to be cast from…etc.
Don’t let cost scare you away from making molds at home!  I’m going to show you a way to make molds for around a couple bucks using household items.  Yes, the ‘ghetto’ way!  You will be astounded when you see that the detail produced from hand casts is far better than most of the mass produced plastic gaming products.
So here we go (photo 1 shows what we will be making):
Not too long ago, I decided that I wanted to make a set of wands for a figure.  I wanted my masters to look as realistic as possible, so my choice of materials is going to be natural objects.  I went on a walk and found some interesting sticks and picked up a couple of quartz crystals off the ground (yes, where I live, there are places you can just pick crystals off the ground…lol).  I superglued the crystals to the sticks.  Next I wanted the wands to be able to swivel in the hand of my LEGO figure so I found some appropriate sized beads and glued them to the opposite end.  Now I have my set of three wands; one plain one, and two with crystals at the end (photo 2).  It is time to mold them so I can have multiple colors to choose from and play with.  Yay!
I know that my masters can withstand heat, so this means I can make my mold using material like Sculpey III and hot glue.  I chose to use Sculpey III because after it is baked, it has a minute flexible quality that will help assist in removing the master.  I chose to use hot glue gun material for the top because it provides even more flexibility yet still retains its rigid casting shape.  Because one will melt easily with heat, and the other will not, I have to make the mold so that the hot glue side is fabricated last.
First I coated my masters in vegetable oil so they would release from the mold easily (photo 3).  Too much oil will lessen detail or dissolve the material (depending on what material you are using) so I use caution here.  I flattened a piece of Sculpey to about 1/8 inch thick (photo 4), then I gently pressed the masters into the clay to their midpoint (photo 5).  This midpoint is going to be the planned seam for the mold.  Next I have to compress and push the clay against the masters because when I pressed them in, it created a tiny rounded curve that did not terminate sharply where the seam line is going to be (photo 6).  I do this with a toothpic that has been shaped like a flat screwdriver.  When I do this, it leaves lots of tool marks in the clay.  For easier mold cleanup, I smooth out all these tool marks with the rounded end of a paint brush (photo 7).  I then need to make sure that there are some alignment points on the mold so that when the two sides are put together they mate perfectly without an offset seam.  I make those points by simply pressing the rounded end of a paintbrush into the clay in 3 places (photo 8).
(In my next post I will continue.)
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Posted: 22 January 2012 10:11 AM   [ Ignore ]   [ # 1 ]
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Nice one grin You make it look simple..I´m really bad at making molds hmmm
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Posted: 22 January 2012 12:10 PM   [ Ignore ]   [ # 2 ]
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TY Paul.  Yes, some of the ways I mold things are very hard.  This method I would rate about a 6.5 on a scale from 1-10 for difficulty.  The hardest part comes next:
(For some reason, the pics are out of order here; so you will need to hoover over them to see what number they are.)
I trim the mold so I do not waste unused Sculpey, making sure to leave just enough room for attaching a clay dam around the piece (photo 9).  Then I bake it.  After it is done baking and cooled, I paint the sides and surface of the mold with vegetable oil being careful not to get too much oil on the masters that were already coated.  (I forgot to take a picture of that step to show, but if I forget the oil, I will probably end up destroying the mold trying to separate it later.)  I roll a piece of general sculpting clay (the generic kind that never hardens), and form a dam that is about 1/4 inch high (photo 10).  The generic sculpting clay is an oil base product that does not harden with heat, so I keep in mind that it can not withstand high temperature long before it turns to mush.  Here is the hard part:  I need to inject hot glue from a typical glue gun onto the masters, and I need to do it quickly.  I absolutely do NOT want to do this if I think there is any moisture or water in my masters because it will cause boiling bubbles in the hot glue and that will mess up everything.  I also need to inject it on every part of EACH master.  What this means is that I have to hold the nozzle and trace around the masters creating a positive pressure flow using the glue gun trigger.  If I notice any bubbles in contact with the master (one is able to see through the glue), I have to move the nozzle back and inject that location again until the bubble moves away from that critical surface.  With this in mind, I inject quickly, check for bubbles, reinject if needed, and make sure my glue gun tip does not come into contact with the clay dam (because it will liquify the dam and make a mess).  I make sure to fill the area up with enough hot glue to make a nice flat surface at the top of the dam (photos 11 and 12).  LOL…. hurry and stick this in the freezer before the dam melts.
I don’t actually want to leave my mold in the freezer very long.  All the freezer is intended for is to quickly harden the dam and cool off the hot glue.  Once this is done, and I can no longer feel warmth in the middle of the mold, I begin to peel off the clay dam.  This clay tends to stick well to the glue so often times I use my fingernail to scrape it out of the hot glue surface. 
Now it is time to separate the mold parts.  I make sure that the mold is back to room temperature or even a little warm from the heat of holding it in my hand.  This makes flexing the sides easier.  Since the glue side has more flexibility than the Sculpey side, I peel it away first, leaving the masters attached in the Sculpey.  When the glue side is off, I flex the Sculpey to gently remove the masters without breaking them.
What I am left with are two sides of the mold, and they are dirty with generic clay around the surfaces.  The clay is oil base and will NOT come off with water.  I have a general rule when I make a mold like this to Never try and clean a mold with soap and water.  I use vegetable oil and a toothbrush to scrub them up.  Then I rinse them off with water; never soap.  I dry the mold pieces off with a hand towel (the type found in a bathroom; not a kitchen).  The hand towel can be pushed into the mold to soak up any thick oil that is left in it.
I end up with a nice mold for casting (photo 13).
Note that not all oils are the same, and some oils will even eat up your Sculpey or hot glue material.  Generally when I use oil for making molds it is generic vegetable oil found in the grocery store.  That oil is usually safe for what I have described here, and is made up of a combination of about 4 common oils.  When I show you casting with this mold in the next section, this concept will become most important; but for now I use an oiled cloth and clean up my glue gun with it before it is unplugged.  It makes it look like new ...lol ... The one in the pic is 25 years old.
(In my next post I will show you how I cast with this mold.)
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Posted: 23 January 2012 11:53 PM   [ Ignore ]   [ # 3 ]
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Casting
One of my favorite casting materials is 5 minute epoxy.  In recent years, casting with epoxy has become much harder because the manufacturers keep making it better and better….lol.  In other words they are making it so that it cuts through grease like a detergent.  For molding purposes, this is not good because it means that generic vegetable oil can no longer be used as a mold release.  I found that the oil from peanut butter CAN though (at least until they make it better).  No need to make a special trip to get oil, just pull the peanut butter out of the cupboard and dip your application brush into the oil that has collected on the top.  You only need a little bit.  In the example below, I’m using Gorilla 5 minute epoxy.
I coat my mold with peanut butter oil all over, top, side, and bottom (photo 1).  Then I wipe it down with a hand towel (photo 2).  I pat it down well and make sure there are no puddles in the molding area (photo 3).
I choose some craft paints that I think might look good as a pigment and begin to blend them with the epoxy (photo 4).  Sometimes I try to get fancy and do multiple color castings.  I apply the first color (photo 5).  Then I apply the second (photo 6).  Looks pretty sloppy, doesn’t it?  lol Trying to mix fast, apply epoxy, AND take pictures is not as easy as one might think.  Anyway, when the mold is squished together, it will push out the excess (photo 7).
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Posted: 24 January 2012 12:06 AM   [ Ignore ]   [ # 4 ]
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Casting (continued)
I let the casting sit for about 15 - 20 minutes before trying to separate it (photo 1).  Even though this is 5 minute epoxy, if I try to separate it early, it will rip the casting.  (I make sure to pull them apart before an hour or two passes, or I will have a hard time cleaning up the mold.)
I was actually able to make 4 master molds of each wand before the little pieces of wood shattered while extracting them.  This means I can form an assembly line of molds and do multiple castings in the same sitting (photo 2).  Whooot!  check out the center ones of this batch (photo 3).
I will let these set for a few days, then trim them up when the epoxy has had a chance to harden.
(That is just one way I make molds and do castings.  In the future, I plan on sharing some others.  Thanks for reading this… now SHOW ME WHAT YOU CAN DO!  I am anxious to see what others are making!)
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Posted: 24 January 2012 12:15 PM   [ Ignore ]   [ # 5 ]
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I trimmed and washed some of them up.  They look nice.  The detail in the wood is great (photos 1 and 2).
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