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Scratchbuilding
Methods - Tools - Casting Parts
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Methods -

Scratchbuilding is just what it sounds like - building something from scratch. Often times there are no kits available of a subject you may like. For most model builders, they would simply sigh and accept the fact that they can't have that ship. But you don't have to do that! You can build that ship or vehicle yourself, from scratch! Scratchbuilding is most definitely harder and more involved than kit building, but the satisfaction of creating something from nothing with your own hands and mind can be very rewarding. Scratchbuilding takes a lot of time, effort and a lot of materials. Be prepared to spend a lot of money and a lot of time just thinking and planning. And be prepared to make mistakes even though you planned so thoroughly. In the planning stage, you need to figure out just how you will scratchbuild that ship or vehicle you want. There are two basic methods of scratchbuilding: traditional scratchbuilding and kitbashing. The two can also be mixed and each method has it's own categories and variations.

1. Traditional Scratchbuilding - Traditional scratchbuilding is the most time and material intensive. It involves fabricating all of the parts of the subject yourself. This process yields the most accurate finished product as you can make the model as accurate as you want. The most common way that people achieve this is by cutting and gluing polystyrene sheet, rod, and strips from companies like Evergreen, Plastruct or your local plastic supply company. You can also use plastic" For Sale" signs from Wal-Mart. To do this, you must visualize how to make a complex shape out of flat pieces of plastic. It is best to plan it out first on paper, and then cut and fold the paper to see if your plan works. For example. If you wanted to build a cube, you would cut 6 squares of plastic, and then glue each side to each other to make your cube. Get the idea? This box building technique is very simple and works best with parts that have plain, angular surfaces.

Curved surfaces can be difficult to achieve with this method. Curved surfaces are best achieved by making ribs out of the styrene that mimic the curve and then filling the space between the ribs with a product like Aves Apoxie Sculpt. This is similar to how boats have curved ribs framing the hull, except instead of covering these ribs with planks of wood (which you could do with plastic), you fill the spaces with filler putty. The most important thing to remember with these methods is that you will have to do a lot of sanding and seam filling. As accurate as you can be, there will usually be some seam you will have to fix. This is normal.

If you have more complex shapes, you can combine both of these methods, or you can try to carve the piece of out a high density foam like Renshape or Balsa Foam. These are difficult products to work with and can be easily damaged so use them as a last resort. A more common solution is to carve your piece from balsa wood blocks. However, you will have to deal with the problem of wood grain and other problems associated with wood. I don't like to carve parts as it is just easier to use the boxing method described above to make the basic shape and then continue building the shapes until I achieve the final look.

Traditional scratchbuilding has been around for a long time and has many more ways to create parts than just the ones I described above. You can use a lathe to make rounded parts, mill complex patterns and shapes, or even use rapid prototyping to "grow" parts. Traditional scratchbuilding involves incorporating many different methods of building to make your ship or vehicle. No one method can do it all. And, like everything else in life, practice makes perfect. Just start cutting paper and cardboard into shapes and see what you can make. Learn from your mistakes and when you finally start using good plastic, you'll do fine. You'll always learn new tricks and will be amazed at what you can do. Good luck!

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Styrene plastic stock needed for scratchbuilding.

2. Kitbashing - Kitbashing is the other major method of building models from scratch. Kit bashing is essentially taking parts from various model kits and putting them together to make something new. This produces a less accurate finished piece as you are somewhat limited as to what you can achieve with the parts you have. For example, you can't expect to make an accurate X-wing fighter by "bashing" other parts. Where would you get a fuselage? Wings? This is not necessarily a bad thing, just a difference from traditional scratchbuilding. Kit bashing is best for making a ship or vehicle that doesn't exist in print anywhere already. You have to be very careful with kitbashing as parts can be very recognizable and viewers may see you as uncreative or unimaginative. I wouldn't think this as I believe it takes a good amount of creativity to put together things never put together before, but others might so be aware.

Kitbashing doesn't necessarily have to mean to kitbash to whole ship. A very common method of detailing a model is kitbashing. Do you know what famous movie models have kitbashed details? How about almost every single Star Wars craft? Kits like the Saturn V rocket, Sherman tank, and numerous others were stripped of their detail pieces to help detail the greeblie areas of Star Wars movie models. I like to kitbash parts to detail my models all the time. It's a great way to add that extra touch of realism to a model. The only catch is that you need a healthy supply of detail parts. Pick up kits at garage sales, find lots of old, cheap kits on eBay, stuff around the house like pen parts, electronics, anything will work. You'll quickly find you have too much, which is good. With kitbashing, somehow too much is actually never enough. :)

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A good selection of spare model parts is needed to kitbash.

 

Tools -

Coming Soon!

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Casting Parts -

Making castings of parts you have scratchbuilt is the best way to ensure symmetry and matching details on your subject. It also saves the headache of having to re-build an exact duplicate of a part you have already made. Molding and casting pieces is a relatively easy process that can be expensive. But trust me, it is worth that little extra to get a perfect copy.

The first thing you need to do is gather your basic materials needed for casting. This includes RTV (room temperature vulcanizing) silicone rubber, urethane casting resin, mixing cups, and mixing sticks. There are few different kinds of materials you can use to mold and cast, but silicone rubber and urethane resin are the best all around choices. They replicate the best detail, have negligible shrinkage and are less toxic.

Once you have your materials, you'll need to plan out your mold. A simple, one piece mold will often work and is the easiest thing to do. A one piece mold can be made of any part that has a flat back surface that can serve as your pouring hole. When deciding if your surface can work, you have to take into account the rest of the piece, and if it will get locked into the mold. The surface you choose will be secured to the bottom of the mold box and, when the rubber is cured, will be the top of the mold. You have to think about if you will be able to remove this part and the castings from the mold after the rubber has cured. For example, if you were casting a part shaped like a truncated triangle, you would use the larger part of the triangle as the base. This way, it tapers down into the mold and will not lock in.

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Molding Diagram - Click To Enlarge

Figuring out your mold configuration is the hardest part of casting. Once you've got this figured out, molding and casting is easy. If you have a part that won't work in a one piece mold, you'll have to do a more complex two or even three part mold. For now, let's just concentrate on a one piece mold.

To make a one piece mold, the first thing you'll need to do is make a mold box. I'll share with you my method I use to make mold boxes. I like to think I invented this method. I'm sure other people out there use this method, but I've never seen anyone. It's super easy and makes the cleanest molds you'll ever see. First you need a sheet of Elmer's foam board. This is about 2 bucks at Wal-Mart for a 20" x 30" x 3/16" board. Why use this you ask? Because it is a sheet of foam laminated between two water resistant sheets of paper. This is the key to making my mold boxes. What you do is first mark out all 5 sides of your mold box on the sheet. See Figure 1. Leave at least 1/4 to 1/2 inch of space around the master part on the bottom part of the box. Once you have all the sides marked out, do the same on the backside of the sheet. Then, lightly score one side of the board along the lines as seen below. See Figure 2. This will be the backside, or outside of the box. Don't cut all the way through the board. Fold these scored lines up to make your open top box. The inside surface of the mold box will be the side of the board that isn't cut. This prevents seams along the bottom of the box that you would otherwise have to seal with glue or tape. With the sides folded up, tack them in place with pins. See Figure 3. If you cut the lines straight, you should have a perfect, water-tight box with no seams that need filling. I have seen people cut plastic sheet or foam or even use Legos to build mold boxes. However, these all require sealing the seams on the box because all the sides of the box are separate pieces. With my method, the only seams are in the corners and, if you cut accurately, they will not leak. It saves a lot of headaches of fixing leaks and uses less material. It may sound confusing, but try other methods and you'll see the advantage of this method.

Once your box is built, secure the master part to the bottom of the mold box with Klean Klay or some Elmer's Glue. See Figure 4. Just make sure it is fully secured and no rubber will leak underneath the part. I like to smear Elmer's Glue All around the bottom edge of the part to ensure a tight seal. Once that is dry, measure how much rubber you will need by pouring water into the mold until it covers the part fully and with a little extra on top. Pour out this water into a measuring cup and that will tell you exactly how much rubber you will need. When the mold and master part are fully dry, you are ready to use the RTV. See Figure 5. First, measure out equal portions of part A and B (half each of your total amount) of the RTV in separate cups and then mix them in a third cup. See Figures 6, 7, 8. The rubber I use calls for equal portions of each. Other rubbers have different mixing ratios so be sure to check yours. Make sure you mix up just a little extra as the rubber is quite thick and is difficult to get every last bit out of the cups. There's nothing worse than running short while pouring your rubber. It is very important that your rubber is fully mixed. Scrape the sides and bottom of the cup several times to get everything. Once the rubber is evenly mixed with no swirls, start pouring it in a thin little stream from high up into a low corner of the mold. See Figure 9. This allows the rubber to flow evenly around and over the part and avoid any air pockets. Keep pouring until you use all your mixed RTV and the part is fully covered. Don't worry about putting mold release on the master part. As long as the surface is not porous, the rubber will not stick to it. Silicone rubber only sticks to itself. Once the pouring is done, set the box on a level surface and let it cure for the full time required. See Figure 10. The rubber I use says to let it cure for four hours. Once the mold has cured, you are ready to starting casting parts in resin.

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1. Mark out your box
2. Score the back side
3. Fold & tack
4. Secure master part
5. RTV supplies
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6. Carefully measure
7. Pour together
8. Mix thoroughly
9. Pour into mold box
10. Let cure

Ok, so your rubber has cured. That's good. Now you are ready to pour some resin. First you'll need your resin casting supplies. See Figure 1. I use a two part urethane casting resin that uses equal parts of A and B like the rubber. You'll also need mixing cups, a mixing stick and some talcum powder. First, let's start off by removing your mold and master part from the mold box. Remove the pins holding the box together and pull down the sides of the box. See Figure 2. You should have absolutely perfect and sharp corners. This means no rubber leaked at all. One of the benefits of my foam board box. Next, carefully peel the rubber away from the bottom of the box. See Figure 3. Do this slowly and your mold should easily come off the master part. Silicone rubber can stretch quite a bit so don't worry if you have to flex it to get the part out. Just go slowly and be careful and you'll do fine. As I said before, silicone rubber only sticks to itself so the part should come out smoothly. When you've got the mold removed and the master out, clean the mold with some acetone. See Figure 4. This is not necessary, but I have found that it lets you make perfect castings right away. Cleaning the mold with acetone ensures there are no oils or anything in the mold to interfere with the resin.

Now you are ready for the resin. To figure out how much resin you will need, just fill the mold with water and then pour this into a measuring cup to see how much you need. Dry the mold thoroughly after you pour out the water. You may also want to very, very lightly dust the interior of the mold with some talc. This step is not necessary either, but it helps keep resin from creating air bubbles around small details. Just make sure the talc is even and the layer is so thin it is almost invisible. You don't want to create a surface texture on the part. Like mixing the rubber, measure out equal parts of A and B (half each of the total). See Figure 5. Make sure to measure a little bit more than you need. Again, you don't want to run short if you can't get every last drop out of the cups. Now mix the two parts in a third cup and mix thoroughly. See Figure 6. I like to use an old piece of sprue that has a perfect little scraping edge on it. I think it came from the ProShop X-wing. Anyway, make sure it is thoroughly mixed with no swirls. Then you can pour it slowly into your mold. See Figure 7. The resin will start to cure within minutes so you must mix and pour relatively quickly. See Figure 8. Not so quickly it makes bubbles, but fast enough to stay within the manufacturer's recommended "pot life". My resin fully cures is about 30 minutes to a hard, white finish. See Figure 9. Once this is done, the part should just pop right out of the mold. See Figure 10. Again, silicone will only stick to itself so you should have no problem removing the part. That's it! You now have a perfect replica of your original part. Congratulations!

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1. Resin Supplies
2. Un tack & unfold box
3. Carefully remove mold
4. Clean mold with acetone
5. Measure out equal parts
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6. Mix thoroughly
7. Pour slowly into mold
8. Curing
9. Fully cured
10. Remove from mold
 
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