Walter’s Guide to Building Vacuform Models By Walter Mertins

• flat surface (I use a 9” x 11” glass cutting board with little plastic pegs on each corner)

• sandpaper ( I do not use water-resistant sand paper but 60 grid 3M dry paper)

• plastic (liquid) welding cement (I prefer Ambroid Pro-Weld)

• plastic cement (again, Ambroid )

• hobby knife (X-acto) or any other modeling knife

• fine tooth hobby saw (X-Acto fine is what I use)

• epoxy (slow-curing 20 minute works best for me as it flows well)

• masking tape (I like 3M because it is not too sticky)

• A permanent marker (Sharpie medium point)

• cyanocrylate glue (I use plain old Krazy Glue)

Getting Started:

I start by studying the plans and deciding what it is that I want to do with the model: Am I going to modify the existing model to make a larger or smaller variant of the subject? Or I am simply going to build it as it is?
After deciding, I trace the outline of all the model parts while they are still on the styrene sheet with a medium-point Sharpie. I try to mark the parts in such a way that half of the black line is on the plastic part and half is on the styrene sheet.
Cut the major sections using an X-Acto knife; I prefer a slightly used blade. Score deep but not all the way through into the styrene and then, using a downward motion, snap the plastic apart.
Place the knife at an angle to the individual parts and score around their contour. Again, score hard but not all the way through. Always carry all the scoring lines all the way out of the sheet. This will facilitate snapping them apart.
Holding on strongly to the part with your weak hand, use your dominant hand to snap the unwanted plastic away from the part. Once the first break is done, the plastic will almost peel off.

Only cut all the way through on the parts that are too small to hold on to.
When cutting/snapping identical parts like engine halves, horizontal stabs, etc., I always score a number on the inside of the part to identify the matting part.
Welsh is pretty good about placing matting parts side by side, but once you cut them all from the styrene sheet confusion begins.
Snap all the parts and do not worry about excess plastic since it will be sanded away later. Do take extra care around flap tracks, etc.
Do not be afraid, snap away and show the kit who is in charge. Besides, if you break the plastic, you can always fix it by gluing it back. Remember, we are modelers and gluing is what we do best!
With a little patience, you will have this step mastered in no time.
I do not spend much time with the props unless I really have to. Aeroclub makes metal replacement props for most of the Welsh kits.

Sanding:

Ok, here we go! So far, so good. Here is what separates the vacuform model builders from the injection model builders.
Once you finish snapping all the parts from the plastic styrene sheet, you will notice that there is a white line all the way around the parts. (White in contrast to the black Sharpie line you drew, remember?)
Well, this is the styrene thickness, and exactly what you have to sand away. I hope that you haven’t just finished trimming your fingernails because when you are done with this step your fingernails will be shorter, trust me!
Glue or tape an 8 ½” x 11” sheet of 60 grid sandpaper to the cutting board. I leave two edges of the paper free of masking tape.
This is a good time to get some strong adult refreshment!!!
Then, cut lots of 2” long or longer strips of masking tape. Make small handles with the tape and attach to all the parts. For the little parts, improvise, but still make handles for them.
I hope that by now the refreshment is taking effect, because I know this is why most modelers do not like building vacuform kits: THE SANDING.

Again, the black Sharpie line represents the outer edge of the actual part; all the white stuff under it is excess plastic. Not much under the fuselage, but lots of it under engine halves, wings, and horizontal and vertical stabilizers.
The coarse sandpaper will cut the plastic really fast, so try to sand applying equal pressure on the surface of the parts. Use circular motions while sanding and check often for proper fitting and to make sure you are not oversanding.
I usually start with the fuselage bulkheads. Do NOT sand them too much. They usually turn out to be undersized if sanded to shape. Most of the time, I dry fit them to one half of the fuselage to make sure they are going to have the proper diameter.

Then, I move on to the fuselage. I sand both halves a bit a time to be able to dry fit them as I go. Again, do NOT oversand the fuselage halves. This will create fit and shape problems. It IS possible to correct an oversanded fuselage by adding a piece of styrene plastic, but it is best if you do not go there at all. It is better to have a fuselage that is a bit larger in diameter than an ugly, skinny-looking one.
Always try to apply equal pressure on all the parts as you sand.
Again, you can see how important it was to trace the vacuform parts with a black permanent marker before cutting them out of the sheet. As you sand the fuselage and all the other parts down, you will notice that a tiny white strip of styrene plastic starts to peel off the parts. I remove that excess plastic off with my fingernail or whatever is left of it, then continue sanding lightly until the white line is all gone and you end up with a nice solid black edge. At that point, you are done sanding the fuselage. I cannot overstress the importance of dry fitting your parts as you sand. You can always sand some more but if you oversand you have just created more work for yourself.

So far, so good, right? Now, we move to the wings.
The wings are a bit tricky. You’d probably like to just sand them down flat on the paper, but you CANNOT do this.
The trailing edge must be thinner than the leading edge. I found that the best way to do this is to sand the wing flat on the paper just for a few passes. Then I grab the wing and sand the trailing edges on one of the straight edges of the cutting board. After cutting some of the plastic off, sand the whole wing flat on the paper. Do this to both the top and bottom halves and dry fit them as you sand. Remember, the little white line of styrene will start curling up and separating from the wing. This means you are almost there. Sand a little extra off the wing tip, then the trailing edge. The reason you want to sand the wing flat again is to avoid leaving a wedge-shaped trailing edge. Dry fit the parts as often as possible.
By now, if you are not completely covered in plastic shavings, you have done something wrong.

Assembling:

At this point you have fuselage and bulkheads ready. The placement of the bulkheads is very important. I usually make extra ones for re-enforcement, especially around the wing fairings. If you are planning to stretch or shorten the model, make even more bulkheads; this will double the strength of the fuselage joints. Cut a little rectangle-shaped notch at the top and bottom of each bulkhead. This is done to allow the epoxy used to re-enforce the fuselage joint to flow freely back and forth through the whole length of the fuselage. Make sure you sand the points that will form as a consequence of the cuts down a bit. These pointy ends could deform the fuselage shape when you glue the halves together.
Glue the bulkhead to one of the fuselage halves. Do not be shy on the use of glue; the more the better. Just do not melt them! Make sure they are straight and perpendicular to the fuselage. I let them dry for about four hours before I start fitting the other half of the fuselage on.
Engine halves and nacelles are very easy to do. Just lay them flat on the paper, apply equal pressure with your fingers, (which by now should be nice and numb with perfectly round fingernails), and sand away. These parts won’t need too much sanding so go easy AND DRY FIT YOUR PARTS.

Did I mention yet how important it is to dry fit your parts?

Once the bulkheads have dried completely, test fit the other fuselage half.
Make sure that the bulkheads have the proper shape; otherwise, they will distort and misalign the fuselage.
Glue the fuselage halves together. Use thin strips of masking tape to make sure of the proper matting of the fuselage.
After the fuselage has dried, it is time for Clint Groves’ “river of epoxy” technique.

I usually cut a hole on a wing fairing or on the belly where the wing will be mated Then I use 20-minute epoxy because it is not so viscious and flows well. I mix about 5 ml of epoxy for a small fuselage and about 10 ml for a large one. Pour the epoxy into the fuselage and then make sure the epoxy travels along the whole length of the fuselage. Rock the fuselage back and forth, making sure that some of the epoxy travels around the bulkhead as well.
Remember that epoxy does not fuse to the plastic. It only creates a rigid bond. It is brittle and if excess force is applied to the bond, it will break cleanly off the plastic and rattle around inside the model.
Once the epoxy dries, flip the model and do the bottom/top halve.
I use cyanocrylate glue (Krazy Glue) to attach the metal parts like props and landing gear to my models.

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Conclusion:

See, it wasn’t so bad after all. It is a long and a bit tedious of a procedure, but once you get this far, you now have your basic injection model kit. Use the same method/techniques that you use for building your injection models from here on. Just remember that vacuform kits are more delicate than injection kits, so be nice to them and you will end up with a gorgeous-looking model. The more vacs you build, the easier they get.

Questions or comments may be sent via the email link on the masthead.

Walter Mertins