This one used about 135 10" hot glue sticks. In this instructable I'll walk through making a much smaller one that probably uses something closer to 5 or 6 sticks.
I made this project over at TechShop (http://techshop.ws/).
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Step 1: Software, Tools & Materials
123D Make (free)
Adobe Illustrator or CorelDRAW (free trials available)
18"x24" sheets of 3/8" plywood (2x)
Hot glue/hot glue gun
Step 2: Working in Illustrator and 123D Make
Start by browsing the 123D Gallery for a 3D model to use; that's where I found this horse. Import it into 123D Make and select Stacked Slices as the construction technique. Depending on the model you may need to change the slice direction to make it look good. You can change the size on the side, which I kept small for this instructable. When you have something you like, export a vector file and open it up in Illustrator (or CorelDRAW).
In the file, all of the pieces will be scattered around. We're going to be making these casts in "blocks" of four or five layers. Because we're going to want everything to line up exactly, what I did was stack each piece in the file sequentially, using the small red guides that Make generated to keep it all lined up.
After everything's stacked properly (look at my screenshots for reference) draw a square around the form. I would extend the square at least 2 inches beyond the shape of the horse, which will make sense when we're removing the glue from the mold. Next, draw a line straight down the center; after the glue dries and the casting's done we're going to remove it by splitting the two halves of the block. Copy the square and, after double-clicking on one of the slices to access its group, select Edit->Paste in Place. Each piece needs its own same-sized square and the placement needs to be consistent.
Finally, look for any elements that won't be able to be casted using this pull-apart method. Note the ears of the horse; since the horse shape is going to be negative space in the final cut product, those two little holes won't make any sense (see my pic). Remove them (or don't, since they'll be gone either way).
Note: If you want to get as much mileage out of this project as you can, you can take the line you drew down the center and change it so that it doesn't go through the shape in the center, only just the top and bottom of the block. Then you can make a complementary wood sculpture when you're done!
Once that's done, space them out on one or more documents to cut on the laser.
Attached below are my Make file (.3dmk) and the two vector files for the laser.
Step 3: Laser Time
If you've ever used a laser cutter then there shouldn't be any surprises during this part, and if you haven't then you're at the right website!
Cut the pieces out and move on.
Step 4: Organize and Assemble
Once you're done and you have a horrible mess of block halves, take the time to sit down and organize each pair. Order them sequentially, and then get ready to glue them with some wood glue.
The thing to keep in mind is that the more layers to a block, the more glue that's going to go inside of it and the harder it will be to remove the casted object once it's dry. I'd say 4 or 5 is the sweet spot, especially for something this small. It's certainly possible to go well beyond that, something I can verify, but it becomes a great deal more difficult at the end.
The exception is that I wouldn't recommend including the ear layer with any block, instead doing that layer by itself. Looking at the ears, you can see that it would be very difficult to pull the two pieces apart without destroying them.
You can kind of see it in the pictures, but one of my blocks concaves within itself; meaning that no matter which way the block is flipped, there are going to be parts inside that will be hard to access once the gluing starts. Just make a note of that when you're deciding how many layers will go into a block.
Step 5: Final Block Preparation
(I would go back and forth between this step and the following step. This step ends with applying corn (or vegetable) oil to the wood, which should be immediately followed by applying the hot glue. To avoid any delay I suggest doing these steps one block at a time.)
Next up I like to coat the parts that will be making contact with the vegetable oil and glue with some bees wax to seal the wood. This part isn't required but it's more useful if you'd like to reuse the casts and want to avoid damage that might otherwise be done to them during the removal process.
After that, take a paper towel and apply a liberal amount of vegetable or corn oil to ease the removal process and remove sticking. Believe it or not, hot glue tends to stick to surfaces and not let go without a fight so lubricating the inside makes everything that follows a lot easier.
Lastly, tape the two block halves together so they don't move around as glue is being poured.
Step 6: Glue!
Place the block on something disposable, like a scrap piece of wood. You might even cover some of the surface with oil to easily pull the block off, since it'll be making full contact with the glue.
If your hot glue gun has a Low/High setting, select Low. At a lower temperature the bond won't be as strong and it'll be easier to pull away from the wood. If you have a smaller glue gun then it'll probably have a single default temperature equivalent to Low so you'll be fine.
Once ready, start filling the block with hot glue, making extra sure that each crevice between layers gets filled to ensure that all of the detail is captures. There isn't much else to be said, just keep going until you reach the top.
The ears offer a slightly different challenge; because it's just one layer, it's likely that while trying to remove the two pieces the ears will get stuck to the backing wood because of its surface area. It's especially important to lubricate the backing wood here because otherwise removing it will be very difficult.
Here's a video of me going through the casting process for my much larger horse head; the scale is different but the process is the same. You'll also see how I removed them, which I detail in the next step.
Step 7: Removing the Pieces, Clean Up and Final Assembly!
After letting the glue sit for a good while, it's time to extract it. Start by prying it off of the backing wood and removing the tape. The glue is way too strong to pull the block apart, so using the end of a sturdy table I'll station the block so that one half is on the table and the other is off and I'll just put all of my weight on it repeatedly, flipping it over and such so that it'll gradually weaken. Don't worry about the glue piece, it'll be incredibly durable by this point so feel free to get rough.
Once they're removed, examine each piece. You can see in my picture that one of the pieces had some excess glue coming out where it filled a gap between the two block halves, and when I was removing the ears I pulled out some of the backing board with it. I just used a small blade to remove this stuff.
Next, gather all the glue pieces, arrange them in the proper order and orientation, and put them together! It's as easy as putting some hot glue on one end and sticking on another, just be sure to work fast.
And that's it! That's one way to make a casted object with 123D Make. Of course you could go the route of making an object out of wood or acrylic and making a cast of it using traditional casting means, but I thought I'd provide a fun alternative.
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