TUTORIALS - 2
SEAMS
AND
GAPS
How to cure them
by Roland Meunier and Paolo Pizzi
Let's face it, if your model is crammed with expensive resin parts and bristles with photo-etch all over but the basic construction isn't good, the general comment you will get from other modelers will probably be: "what a waste!" Not to mention that "basic first" is rule #1 in any IPMS contest all over the world. A superbly detailed model with visible seams/gaps will be discarded right away by the judges. And that's a real pity because you probably spent hours and hours detailing your creation and what you left out and got you kicked out of competition would have probably taken you just a little extra work.
Curing seams is actually a lot simpler than it seems (pun intended :-) ) All it takes is a little patience and some skill which is easily acquired. These are indispensable ingredients, coupled with a very critical attitude toward your work and the aspiration to do the best you can do (note that we deliberately avoided the word "perfection"...)
Thanks to new materials and better fitting kits, achieving perfectly hidden seams is today a lot easier than it used to be. The techniques we are going to illustrate in this article involve the use of three products that have been available for a relatively short time but that have revolutionized and simplified the basic construction: superglue, Gunze's Mr. Putty and Mr. Surfacer 500.
1. A seamless fuselage
Superglue
(a.k.a. cyanoacrylate) is the best product you can use to hide the seam
which results from joining the two halves of a fuselage (or a hull, if you're
building a ship.) It is very simple to use and incredibly fast. It still amazes
me how so many people haven't tried this and yet complain about their imperfect
work which took them hours and hours with "conventional" (read
1960...) methods.
In recent times, "gap filling"
superglue has been specially formulated for this
purpose.
This type reacts to a cyanoacrylic accelerator (a.k.a. "kicker") in a
way that makes your work even easier. Basically, you use an accelerator for two
reasons: 1. because you don't want to wait until the glue has fully cured to
start sanding and 2. because a kicker produces gradual hardening of the glue
(especially with the gap-filling type), which in turn allows for easier sanding
within fifteen minutes from application (after that the CA glue dries rock hard
and the excess would be much harder to remove.)
The
photo on the left shows your typical fuselage seam before the two halves are
glued together. By typical I mean the one produced by a quality kit (Tamiya
in this case.)
It is really not very much visible once the fuselage has been properly glued, but because this specific model calls for a natural metal finish, extra care is needed to hide the seam, since any metallizer would reveal the least imperfection underneath. This of course doesn't mean that you can be sloppy if your aircraft is to receive a coat of flat paint. Always apply the highest standard you can achieve and you'll be very satisfied with the results.
Though
this strays away from our discussion on seams, I'd like to spend a few words on
fuselage assembly. I know many people using superglue to join the two halves of
a fuselage. My advice is: don't, for a VERY good reasons: superglue dries too
fast (even if you use slow-curing types.) As a result, you may easily incur in
one or both of these problems:
1. Incorrect positioning of the two halves. By the time you realize that part of the joint is mis-aligned, it'll be impossible to reposition.
2. Inconsistency. Since you're probably rushing to lay the superglue before it cures, chances are that in some areas the glue will spill out while other won't bind because the amount was too tiny and had already dried before you joined the halves.
Liquid
glue, on the other hand, is much easier to control and allows for the gradual
bonding of the two halves. You can take as long as you want and, best of all,
you work with the two halves already joined. There is only ONE thing you must be
very careful with: don't touch the glue while it cures or it will permanently
mar the plastic. Apply a thin layer of glue over the seam and let it seep down
the seam. Don't worry about the excess, as long as you don't touch it, it will
evaporate, virtually leaving no residue. I know people (especially in the US)
that use Tenax 7R. This is a very good product but it's highly toxic and
requires some skill (it's easy to mess up with this stuff.) Recently, Tamiya
has introduced a much safer and easier to use product called "extra thin
cement". This is truly thin stuff and cures in about 7-8 minutes. It
comes with a tiny brush applicator which facilitates application and limits
over-spills. After I discovered this product, I don't use anything else to glue
my fuselages.
Enough
with the digression. Now that your fuselage is assembled and the glue has fully
cured, you can start with the seam-filling process. No matter what type of
filler you use (and superglue is certainly no exception) a certain amount of
"heavy" (as in "coarse") sanding is involved in the initial
phase of the process. This may result in a lot of surface details (such as panel
lines and rivets) being obliterated, especially the tiniest ones. You want to
avoid this as much as possible. How? Simple, by protecting any surface outside
your area of work. Apply masking tape (possibly heavy-duty stuff but not too
thick) on your fuselage, leaving the area of the seam uncovered, pretty much in
the same way a surgeon would delimit the area of the cut on the body of the
patient. Burnish the tape down as best as possible.
Especially
when the seam is tiny (as in most good-fitting modern kits), you want to use as
little superglue as possible. I hate applicators, they always get clogged and
never allow you a good degree of control on the amount you apply. The most
practical way to lay tiny amounts of superglue is by way of a toothpick. Pour
2-3 drops of CA glue on a disposable plastic surface (I always use plastic lids
from yogurt cups because they're actually reusable: superglue never really stick
to them and you can remove it, once cured, just by bending the lid), pick a tiny
amount with your toothpick and then transfer it on top of the seam, making sure
that the glue trickles down the joint.
Once
the whole seam is covered, spray the accelerator (kicker.) You will observe how
the glue crystallizes in just a few seconds. Keep your nose closed (or better
away) in the meantime as the resulting (invisible) fumes are very harmful to
your health. Now you have about fifteen minutes before the crystallizing process
is complete, during which the superglue gradually gets harder and
harder.
For this reason, start sanding immediately after the glue appears to have
solidified or you will need a lot more energy to accomplish that.
You can use either sandpaper or sandsticks
to remove the superglue excess, or a combination of both if you want. However I
strongly suggest using a sandstick for the initial coarse
sanding, since it allows you a better control. Even though the areas outside the
seams are protected by the tape,
you want to
go
over them as little as possible.
Remember, a coarse sandstick can do an awful lot of damage! Start with a 150-200
grit stick and work the seam until it's perfectly flat.
You will then use a medium grade stick or paper to remove the larger scratches. Always sand in rotatory motion, never up and down the seam or sideways. Alternate clockwise and counterclockwise movement for an even result. As the large scratches gradually disappear, wet your sandpaper/sandstick and continue sanding.
Once
you're done, you want to remove the protecting tape before you start working
with the finer grade stuff. First because you need to get rid of the inevitable
sticky residue and second because you want to start blending the sanded area
with the surrounding, untouched ones. The best product to remove the gummy
residue left by the masking tape is called "Goo Gone". It is
made in the US but it's widely available overseas. Not only this stuff is
incredibly and quickly effective, but it will also leave a pleasant citrus
scent.
It's
time to switch to a fine grade paper/stick. Always proceed with dry and then wet
sanding. Try to blend the sanded area to the outside ones as best as possible by
lightly going over them. Maintain rotating motion.
The seam has now completely disappeared but your work is not finished yet. The portions of engraved panel lines crossing the seam have likely disappeared and need to be re-scribed. If you have followed my advice and protected the areas outside the sanding, you will only need to scribe segments of only 2-3 millimeters.
I
know some people that use Dymo tape as a scribing guide. But if you are
serious with your modeling, at one time or another you will get a scribing
template. The one made by Verlinden is, in my humble opinion, the best
and it's also quite cheap. A discussion on which type of scriber to use would be
outside the scope of this article (but the likely subject of an upcoming one...)
and therefore I won't expand on that for now.
Now
that panel lines have been restored and the seam is history, all you need is to
polish the top of the fuselage. You can start with extra-fine sandpaper (or sand
film) and then complete your work with the application of a plastic polisher
that will remove the tiniest, almost invisible scratches. This last step is only
necessary if your aircraft is to receive a bare metal finish.
How long does all of this take? Well, it depends very much on your skill and experience. If you are a beginner, do take your time, it will allow you to fully understand the process and know exactly when to move from one phase to the other. I can tell you that for an averagely experienced modeler, it doesn't take more than a few hours. Once again, if the model is to be painted with a metallizer, you want to get as close to perfection as humanly possible.
2. Hiding smaller seams
The technique described above also applies to gaps and other kind of seams, although sometime it may be impractical. Such is the case when the seam is in an awkward position (such as in a fuselage to wing root joint) or if it's surrounded by tiny details and the work area is too small. In these cases there is still room for working with the traditional putty. There is now a better one though...
Your regular filler (putty) has three main disadvantages:
1. It's grainy and coarse and therefore hardly suitable to fill small areas or seams. Yes, you can thin it down with lacquer thinner but it's a very messy affair, not to mention a risky one since lacquer thinner does attack plastics.
2. The excess is very hard to remove. You will need to sand it away, first with coarse and then with finer sandpaper. This will result in a lot of surface detail permanently deleted.
3. It cracks when dry. It seems contradictory that a coarse material like putty can only be effectively used in limited areas but unfortunately it's the truth. That's why large gaps or seams always need to be shimmed.
Gunze's
Mr. Putty looks like your regular filler but it is in fact much more. It
still cracks if laid over large areas, but it does away with drawbacks #1 and #2
of traditional putty. This product has a creamy
consistency
and therefore can be applied virtually anywhere without messing up the
surrounding areas. Once again, my favorite way to apply it in small amounts is
with a toothpick. The best feature of Mr. Putty however is the fact that the
excess does not need to be sanded away, it can be swept away with a brush soaked
in Gunze's own Mr. Color Thinner, a mild lacquer thinner which does not
attack the plastic. This is my favorite medium to deal with medium/small gaps
and seams.
As
an example of using Mr. Putty, I will show you how I reduced a small seam
between the wing tip and one of the auxiliary tanks on my Tamiya F-84G. The seam
was on the lower side of the wing and it's hair-thin. The purpose was not to
hide it but to reduce it and make it consistent throughout its entire length.
The
putty was applied with a toothpick and pressed down the seam with an old
(discarded) brush.
No sanding will be necessary, however I decided to protect the rivet detail on the tank anyway, so that the work area will be reduced.
Once
the putty was dry to the touch (but not fully cured), I used an old brush soaked
in Mr. Color Thinner to remove the excess.
Now I had to wait until the putty had fully dried (12 hours or so) and then re-scribed the line. Extreme careful must be exercised because the dried putty is brittle, but it's still very doable. Et voilą, the seam is now what it should have been in the first place: a consistently engraved panel line.
3. Micro-gaps
While of course mini- and micro-gaps are also found while building aircraft (especially with older kits), these are dealt with on a regular basis by the shipmodeler, especially when working in small scales and/or with resin kits.
I'm talking about those tiny imperfections where none of the above would be suitable due to the extremely small size of the work area. What to do in those cases?
Here's
a very good example. The photo on the right shows a partially assembled
superstructure of a 1/700 scale WWII Japanese Kaibokan (escort.) The kit
is made by Skywave/Pit-Road. Major seams and gaps have already been
cured, but a very annoying dimple of the funnel needs to be eliminated. To make
matters worse, the smokestack has tiny raised details that you definitely don't
want to obliterate. At the same time, I will work on the seam between the funnel
and the funnel cap.
The best product for this kind of intervention is Gunze's Mr.Surfacer 500. While advertised as a coarse primer for scratch-built (as in rough) surfaces to be sprayed to fill minor scratches, it can also be used as a kind of "liquid putty" and applied locally with a brush. As with Mr. Putty, it can be easily removed with Mr. Color Thinner, even after it has fully dried.
I
first apply the surfacer with a brush and let it dry. It will definitely shrink
and conform to the surface, therefore a second and third application may be
needed. Don't worry about the excess, we will brush it away. At the same time
don't exaggerate because it will be a lot more work later and because the stuff
is very expensive and you certainly don't want to waste it.
I
leave the surfacer overnight to dry and then I start removing the excess with a
brush previously immersed in Mr.Color Thinner. Be gentle and take your time or
you may completely remove the surfacer, even that filling the gaps. Soak the
area first and then lightly brush away the excess surfacer.
As the thinned surfacer drips down, pick it up and brush it all over the funnel to achieve an even surface. Once again, you may repeat this several times before you are satisfied with the results. Let the surfacer dry every time.
And
here it is, the funnel is now perfectly smooth while the surface detail has been
preserved. You will later enhance this by carefully laying a dark wash in the
recesses and dry-brushing a lighter color on the raised details.
Mr. Surfacer 500, while an outstanding product, is not "magic" by any mean and still requires skill to be properly applied. If you've never used it, try it with a junk kit first. It would be impossible to describe with words the kind of consistency you are looking for when thinning the stuff with Mr.Color Thinner in order to smooth a surface. It is something that has to be learned by trial and error but once acquired will produce some pretty outstanding results.
FYI, the funnel in the photographs is only 4 millimeter tall, less than 1/4 of an inch!