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P-51B Build Report 2: Main Assembly

July 18, 2010

With the cockpit area completed, it’s time to move on to the main assembly.

Fortunately, the P-51B is a very well-designed and almost perfectly straightforward kit. It’s what’s known as a “shake the box” kit, in that all you have to do is shake the box and the model falls together. I haven’t found it quite that simple, but for the most part, it’s been very smooth sailing.

The first step involves joining the two fuselage halves. In the past, I would have run a bead of cyanoacrylate glue along one half, then tried to slam them together before the adhesive cured. This had the effect of holding the parts together, but it was sloppy. What can I say? I was impatient, and CA can cure pretty much instantly if you spray enough accelerator at it.

This time around, I’ve decided to go a different route, and try something called Tenax-7R.

It’s actually not an adhesive at all, but a solvent. It works by melting plastic so that two touching parts effectively “weld” themselves together. This is basically the same stuff as Testors liquid cement, just a lot spicier. You can actually see the weld working, and it forms a pretty strong bond within about 20 seconds. Big improvement over the “you’d better hold those pieces together overnight or they’ll com

When I was ready to assemble the fuselage halves, I decided to heed some advice I’d read online. Test fit, then test fit again, then test fit again after that. Then tape everything together. Then, and only then, start in the the Tenax, treating small sections at a time.

Working slowly, the fuselage went together without incident. The Tenax fused everything solid. I didn’t actually run into any difficulties until I was installing the lower wing. The problem arose from the landing gear bay and the underside of the cockpit assembly. The former had a hollow area, and the latter a raised rectangular area. These were obviously made to fit into one another, but mine were off by maybe a half a millimeter. This doesn’t seem like much, but it was enough to skew the wing out of position. This led to a good hour of sanding and filing and scraping until I reduce the protuberance on the cockpit underside to a sad swelling of plastic.

After that, everything else went together without a hitch. The upper wings slotted into the lower wing so perfectly that I didn’t even have to apply solvent along the wing root. It was that snug. The horizontal stabilizers went on with similar ease, leaving only a few other bits – the air scoop and radiator exhaust flap – to attach before moving on to sanding and painting.

There are still plenty of bits left. The propeller and landing gear. The flaps and canopy and exhaust manifolds. But all of those are getting painted first, and then assembled. That way I won’t have to mask as much. Because I hate masking.

Seam No Evil

One of the things I’ve wanted to do as I get back into modeling is to work past the weak points in my past work. And to my mind, one of the most glaring weak points has always been the centerline seam.

Centerline seam on the Fail Dauntless

This is the seam left over from gluing the two fuselage halves together. The seam I was always too lazy or too impatient to deal with properly. Either I’d say screw it, or I’d make an attempt with putty and sandpaper, and then say screw it. But nothing destroys a model’s verisimilitude faster than the centerline seam (except a really poorly painted canopy), so I set about reading how to eradicate it.

The first step was using the Tenax to weld the plastic together. This did a pretty awesome job of eradicating the seam, but it also left evidence of its use in some mild crazing of the plastic to either side of the weld.

Obviously a little crazing is a lot better than giant, gaping seams, but it’s still enough to stick out like a sore thumb once the paint goes on.

To kill off the crazing, I wet sanded the entire join with 600-grit sandpaper, then wiped it all dry with a paper towel. And…since I was priming all the subassembly parts anyway, I figured I’d go ahead and prime a few select areas of the main assembly to see how good a job the sanding was doing at hiding the seam. I mean…it felt smooth…but the bare plastic looked pretty nasty and scratched up.

Fortunately, the primer revealed almost no visible evidence of crazing, and no centerline seam whatsoever.

I think there’s still room to go back over with some finer grit paper, but so far, I’m ecstatic about these results.

Next up – priming and painting!


3 Comments leave one →
  1. Kay McDougall permalink
    July 19, 2010 9:27 am

    I’m impressed with all the hard work you’re putting into this.

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