Here’s a vintage article from the archives.. not even sure when this was first published!
Scratchbuilding Primer by A.J. Madison
My advice is to just start carving up styrene.Picture some large sub-assembly you want to build, and go ahead and start slicing plastic. You’ll make mistakes; once I had to trash an entire Saturday’s work because I didn’t conceptualize a structure correctly. However you’ll get a real feel for how the model will go together. And when you complete your sub-assembly, you can begin to estimate how long and how hard it will be to complete the subject of interest.
I strongly recommend some “photocopier” magic.Try and produce a set of plans that are the same scale is your intended subject. You can picture subassemblies in “real size” and you won’t waste time with tedious numeric conversions.
Also, practice additional care with measuring and cutting out parts. Especially with a scale model, inaccuracy in part shapes adds up, and if you have a complex & intricate design, you can reach a stage of assembly to discover that your “fusion thermo-couple turbo-cannon laser” won’t fit without cutting off half of your “wing assembly.” I use a large collection of drafting tools. Mostly dividers (compasses with the graphite swapped with a point) and the smallest triangles sold in Art/Office supply stores. I try and interpolate between marks on the drafting scale when making or taking measurements as well. Do not forget to subtract the thickness of the plastic. Yes, it may only be twenty thousands of an inch for one panel, but a “cube” made of .020 sheet would be a total of forty thousands out of dimension. You’ll definitely be able to see that it’s “out of square”. And in a hobby where millimeters make the difference between accurate and inaccurate, .040 is a millimeter off.
Scratch-building techniques are probably as numerous as the different subjects that are built from them. And without knowing what you want to build, exactly, its difficult for me and or anyone else to point out a set of techniques that will be most useful to you. And before I begin, let me say, scratch-building is not a black-art practiced by modelers with hyper-acute cases of “Advanced Modeler Syndrome” with way too much free time on their hands.Scratch-building sounds scary, it’s not.
But in short, I’d say there’s approximately 4 different major variations:
Possibly the simplest and speediest construction method of the techniques. Kit-bashing involves finding the right, or nearly right shape in existing styrene. Don’t limit your search to just kits. Lots of packaging is perfectly good styrene. For example, I needed a rounded convex shape, and discovered that by cutting the bottom off a movie Enterprise saucer section and gluing it to the top saucer sectoin part of the same movie Enterprise kit, I got the exact profile I wanted.
Also, Evergreen & Plastruct make a large variety of shapes. Tubes, miniature I beams, miniature columns & channels, various rod and square stock. I built a pair of warp engines based primarily on pieces of Evergreen rod that happened to be exactly right diameter. Before resorting to the last two techniques below, see if the shape of interest can be built up from these simpler elements.
“Boxing” it in
Treadheads use this technique alot, partly because simple techniques produce advanced results (no knock on their skills, hardly) and partly because the final product is rather straightforward. One need only build whats on the plan (though the AFV’s weapon might not be straight forward at all.) Sheet styrene is cut in the appropriate polygonal shapes and glued together.The problem with this technique is that the object of interest needs to be planar in form. Good for some/many AFVs, useless if you want to scratch a “Globemaster II”.
“Wrap it Up”
I would call this die-cut Balsa wood kit technique one. Its a variation of “boxing it in”. Your shape has a curve in one axis, not necessarily circular, but it is a shape that a sheet of styrene can assume without cracking or tearing. This technique is good for building the main sections of an aircraft wing and some ship hull shapes.You start by building a frame with some center spars (or keel) with ribs at intervals either dictated by the real subject, or sufficient to keep the covering sheet of styrene from caving in. Depends upon your subject, but avoid ribs more than 1″ (~2.5 cm) apart.When your frame is complete, wrap it in sheet styrene. 5 thou sheet is very flexible but you can easily sand through it. 10 thou sheet is thicker but not as flexible. An alternative solution is two layers of 5 thou, but care is needed gluing the layers together, lest the outer layer get kinked by the inner one. But provided the curve is gentle, you can use several layers in order to build up the final shape. I had one subject that I laminated six layers (three top, three bottom) around a curved frame to obtain the final desired shape. The additional laminations were necessary to provide recessed details in the final shape.
“A+B Epoxy” to the Rescue
Call this die-cut Balsa wood kit technique two. It is also the technique of last resort, because it can solve just about any problem one can think up. In most cases the desired shape is composed of compound curves. The first time I saw this technique was in a FineScale Modeler article on scratch-building a then unavailable 1/72 scale X-29. Once again, one builds a frame, composed of a series of ribs (and longerons if so desired or necessary). Not unlike previous method, the frame roughs out the final shape. However, because of the compound curves, you can’t just cover the object with sheet styrene. However, you can use A+B Epoxy (if unavailable in your area, Milliput or plumber’s waterproof “putty” epoxy will work, albeit at greater expense). In the X-29 article mentioned above, it may be necessary to pre-fill the area between ribs with balsa wood to keep the weight of the model down (consider 1/4″ to 1/2″ external layer of A+B sufficient). Once that is done, fill the ribs with A+B. Try to knead the bubbles and voids out of the A+B otherwise you’ll need to putty those voids after you achieve the final shape. Once the A+B has cured (about 24 hours), start standing with a low numbered grit sandpaper. 60 or 80 grit is fine until you’ve roughed out the general shape. Start using progressively finer grits until the ribs start showing through the A+B. This sounds time-intensive, its not. I sanded out the final shape on one subject in a single evening. Admittedly, I spent a great deal of time later wet-sanding the project to get a glass smooth finish that was also absolutely dead-on in profile, so you can put in as many hours as you want during this stage of the detailing. This technique also works amazingly well with profile correction. I was able to wet-stand the A+B until it was actually translucent.It neither detached itself from the model, nor chipped away at the edge of the A+B where it blended into the model.
Obviously, any scratch build project will consist of several of these techniques. Try to map out how you’re going to accomplish a major assembly first before actually building. And you’ll be impressed what you can “free-hand” and have it still come out looking perfect. So don’t get hung up on certain details, if you can build the major shapes, the details are usually easy to coax in later.