R/C'ing the Revell 1/72 GATO Class Static Submarine Kit, Part-11

A Report to the Cabal:

The first use of primer on this project, and working out the mechanics of how I'll secure the upper to the lower hull half, was on the agenda the last couple of days. Concurrent with that has been the creation of a new set of propeller masters for this model. More on the propeller work soon.

Time had come to spray on some primer to check for file and sanding scratches and to check for overall contour symmetry in the filled areas: the bottom, near the keel and the sides, where I had split the upper from the lower hull.

These things are easy to identify if the object is of a uniform 'neutral' color, such as ... er ... primer gray.

Primmer does three things for us: As mentioned, it makes it easier to see imperfections on the objects surface. The primer is the film interface between the plastic parts and the later filler and putties that will be applied to fill scratches, seams, and re-contour. When laid down heavily the primer is a thin film filler -- it can be shot from the gun thick enough to qualify it as a filler, very useful when used to perform subtle re-contouring of the objects it's applied too. And the final coat of primer becomes the foundation for the paint.

The characteristics you want in primer include the ability to stick to what you spray it on (various type plastics, wood, metal, paper, etc.). To be receptive to a tight bond to things applied over it (more primer adhesives, putties, fillers, and paint). And you want your primer to be quick-drying and you want it to be benign to the material it's being sprayed over.

The DuPont Lucite brand, automotive acrylic lacquer, Fill 'N Sand 131S, primer you see above meets all the above requirements. (By the way, out of the can, 131S is 'Mr. Surfacer').

After the initial primer coat I applied Evercoat filler to trouble areas that evidenced themselves in the shadow capturing gray. I discovered open seams, file and sandpaper scratches, and areas that needed re-contouring. These were marked in pencil and addressed.

Here I'm using a stiff brush to apply Evercoat Metal Glaze filler into and around the seam between upper and lower hull. The trick is to quickly run a narrow knife blade into the gap after applying the filler, or the filler will 'glue' the two hull sections permanently together. What this process does is to achieve a tight fit between removable sections that has a natural gap equal to the width of the knife blade.

Applying the filler to the upper/lower hull seam. Metal Glaze filler, unlike most other formulations of a heavily filled polyester resin material, has a very thin consistency and is ideal for application with a stiff brush. The reason for using the brush here and not a putty knife or screeding blade is that the low pressure of application produced by the bristles does not tend to drive the filler too deeply into the seam, which the other tools would have done.

Of course, I have to get the gross amount of filler out of the brush before it starts to set up and to dunk and scrub the bristles in lacquer thinner or Acetone if I'm to save the brush for future jobs.

After the filler had cured enough to work, about five-minutes, I put Rose to work with a

double-sided #100 sanding square to knock off most of the filler on and around the upper/lower hull separation seam. Later, I came in with a soft block outfitted with a piece of #240 sandpaper for final shaping.

You back up a piece of sandpaper with a stiff or soft block in order that the abrasive assume a none or slightly flexible posture when being dragged over the work -- too flexible and the sandpaper will conform to dips and high spots, not revealing or knocking down such areas, which is the intent with most sanding operations. The hard block can be a piece of wood, stiff plastic or metal. The soft block is a piece of rubber, a folded up towel, or foam. Here I'm using a 'soft block' sanding tool -- a hunk of 3/4" thick Styrofoam sheet backing a piece of #240 sandpaper -- to knock down excess filler left from the seam tightening job.

The second layer of primer is applied after I had don more filler work on and around the upper and lower hull separation seam. Now, things are starting to look good. Other than a few pits and sanding marks, the seam area is now well contoured and hardly noticeable -- I've brought the fit between the two hull pieces to near perfect registration with a seam of only 1/32" width. Not bad!

When filing and sanding to maintain or re-contour a surface, the amount of and position of your shop lighting is important: you want the surface of the work to throw shadows on and near the areas you are rubbing the abrasive. Strong, non-bounced lighting is important here, you want to see sharp contrasts. Remember, primer is not only a friendly substrate for further filler, putty and eventual paint application, it's also a buildup medium that is used as a filler to slightly contour the work -- build up a thick layer of primer, then sand it back with control and you can correct/change the shape of the work.

Primer IS NOT gray paint!

The upper hull half overhanging deck piece at the bow is flimsy and needs a positive means to secure it down tight onto the lower hull bow section. I devised a scheme where three (two seen installed and working here) compression catches mounted onto the bottom of the overhang, when slide forward a quater-inch, engage the three transverse pieces of upper hull.

I bent the compression catches from brass strip and bent the forward ends so they will slide under the bow transverse section, pulling the upper deck overhang down tight on the bow. This takes care of registering and holding the bow of the upper hull down onto the lower hull. Aft, a single 4-40 machine screw does the work of holding the after section of the upper hull down tight on the lower hull.

I've worked out compression catches to hold the forward section of the upper hull down tight onto the lower hull. Back aft, here, you see the brass fitting I put together that serves as a foundation for the single 4-40 screw fastener that will hold down the after section of the upper hull down tight onto the lower hull. This foundation has two tapped holes that permit its permanent installation to the lower hull (within the after upper portion at the stern) A turned brass foundation extension is tall enough to make contact with the inside of the upper hull when the two are assembled together, nice and tight.

With the after mounting foundation in place within the lower hull you now see how it works. First, the bow overhang is positioned about a quarter-inch aft of where it belongs, as the upper hull is slide forward it engages the compression latches, which secures the forward end of the upper hull to the lower hull. I then slip a short 4-40 flat head screw through a hole at the after end of the upper hull (where the after flagstaff would go), push the upper hull down, and screw the fastener home. And that's all there is to assembling the two hull halves together.