Fuselage seams - need some help...

Paint has a wonderful ability to reveal the smallest imperfections. It sounds like you may have a small gap where the two halves meet. If you want the seam to disappear, the gap must be filled. There are lots of seam filling tutorials around, such as

www.aeroscale.co.uk/modules.php

I basically go over every seam with thin CA glue. The thin stuff can get into the smallest of gaps and it doesn't get rock hard like the gap filling CA glues do. Once the CA has been applied and sanded smooth, I shine a flashlight on the seam from all angles (Contest judges do it, so I figure I should too).

Priming is also a helpful step. I use a gap filling primer like Alclad II's white or gray micro-filling primer. If the primer reveals the seam (as it often does) then I spray multiple light coats on the seam followed by more sanding. A particularly nasty seam may require a repeated application of primer and more sanding.

As for fixing the seam on your Mossy, there is one trick I used with success that didn't require stripping all the paint off. Sand along the seam to remove the paint, then brush on a heavily thinned primer. I used Vallejo's white polyurethane primer heavily thinned with their airbrush thinner. This requires several coats of the very thin primer, followed by sanding after a few applications. Then repeat until the seam is filled in. Then spray your color coat over the seam and blend it into the rest of the paint.

One thing that helps is to let the glue cure for a couple of days.  I know that if I use Testors Liquid cement, for example, and I sand it after a few hours the seam will reappear.  I believe this is due to the chemical process of the glue and styrene not being complete.  If I wait 2 or 3 days to sand the seams do not reappear.

There are two different problems with fuselage seams.  The first is a gap between the parts- for instance joining sides are not parallel, and a gap results.  This is a pure fill and sand problem.

The second is unique to things like fuselage joins, wing joins, etc. where there are two seams to the join.  In this case, if the two parts are not exactly a mirror image- say one side is larger than the other by only a few mils, you will get a bump on one seam or the other.  Or, by careful placement of parts before clamping, you can share the difference between the two, creating a need to level both seams, but by only half the distance.  It is almost impossible to accurately form the desired section, but you do the best you can.

Besides sandpaper, there are two methods to shaping/smoothing seams- scraping, with a knife blade held at about 90 degrees and pulled along seam, and needle files that remove plastic faster than sandpaper but with smaller scratches.

Thanks guys.  Much appreciated.  I decided to break out the Mr Surfacer 1000 and dab it on, the seam now looks a bit like it's been spot welded.

Just waiting for the Mr Surfacer 1000 to dry (I'll leave it for 24hrs) and see how sanding goes, but I can already still see the seam showing through the Mr Surfacer.

Could be inherent in the kit. Sometimes the halves aren't quite totally half round. A little less than, so you get a ridge.

I think it's what Fly-n-hi described, because I did sand it the day I glued it and I applied the first layer of Tamiya RAF MSG the same day also, although I'm sure I could still see the seam then.

Just hope the Mr Surfacer sands down nice and smooth and I don't get a ridge line where the Mr Surfacer meets the rest of the plastic/model like I usually do...

This is my 2nd attempt at the same kit, the 1st I had to chuck because I got the camo colours the wrong way round, tried to strip it using Fairy Power Spray, failed miserably (probably because I had left the paint a week or more and it had cured, although Fairy Power Spray stripped a 20 year old metal figure for me!?!) and was left with an utter mess.

On that attempt though I sprayed Mr Surfacer 1000 over the fuselage seam and it went on beautifully and covered the seam perfectly...

...but it also ruined my airbrush and didn't spray very well at all (I didn't thin it)!!

I really wish there was an acrylic version of Mr Surfacer because I can't use cellulose thinners due to the fumes (I do my modelling in my dining room) and it's bad enough just using Mr Surfacer neat.

An extra coat or two of Mr. Surfacer from the spray can usually works for me, to remove those residual seam lines.

Hello!

Oh it's a bad problem! Had it many times before. We're talking about shrinking filler here - you can sand the seam pefectly smooth, then paint it, and then the filler shrinks - even under a coat of paint - and the seam shows again. Most one-component modelbuilding fillers and Mr. Surfacer tend to behave like that. My solution here is to glue the bigger parts of the model with nitro lacquer thinner (acetone, MEK, stuff like that) and use sprue dissolved in the same thinner for filler. This home-made thinner, apart from being dirt-cheap, also has the big advantage that it does all of the shrinking in the first 24 hours. After that it sands very smooth with excellent adhesion to the surrounding plastic - so that's what I use for filler almost exclusively. Hope it helps, have a nice day

Paweł

You likely have a lot more experience than I on joining fuselage seams, but I think if you used gap filling Super Glue, like Zap-a-Gap, your problem would be solved. It's possible that there's too much glue on the edges now, but if you can clean out that Testors glue and run a bead of Super Glue along the edges and squeeze them together till some of the Super Glue oozes out, and let that cure a couple days, you should be able to just sand that smooth and then fill any remaining spots with your Mr. Surfacer, and then sand it smooth. This is how I do gun barrels, and it works wonderfully.

Thanks for the advice guys.

Mr Surfacer 1000 sorted the problem out nicely.  I've still got a bit of a visible mark (mostly the Mr Surfacer where I blobbed it on over the seam) but that's because I didn't quite sand it down enough, it's only really visible if you look at it very closely, and will probably only look worse in photos if the camera picks it up.

I guess what I should have done was left the poly cement to cure overnight, then put Mr Surfacer over the seam and sanded it all back before I put down a layer of paint.

Must learn patience...

One reason I use putty rather than gel CA is that it is much cheaper.  Oh, I will put down a small drop of CA for a very small imperfection, but for major seams I reach for the putty tube.  While it does shrink a little bit, I have never found this to be much of a problem.  If it is a reasonable gap seam, the depression of the putty can be filled when I prime.

Also, gap filling CA dries hard. Much harder than the plastic around it. That is then almost impossible to sand smooth.

When I first came back into the hobby 10 years ago, the use of CA for filler was hot on this forum. I ruined a couple of models trying to get it right.

I Cheat !

  When doing a plane I do this .At the time I put the fuselage together I let it dry for a day or two .Then sand it down . If it has a seam I fill it with my favorite -3-M Glazing putty .That's hot stuff so use carefully Then sand again .Then take a drop of C.A on my finger and Swipe it down the whole seam .No more problems .        T.B.

GMorrison

Also, gap filling CA dries hard. Much harder than the plastic around it. That is then almost impossible to sand smooth.

When I first came back into the hobby 10 years ago, the use of CA for filler was hot on this forum. I ruined a couple of models trying to get it right.

Another plus for needle files.  Files cut the CA very nicely.

Yep. Needle files make quick work of hardened CA.

I use either Plast I Weld or Tenax applied with a Touch N Flow applicator then I press or squeeze the parts till a small ridge of melted plastic oozes out of the seam and left overnight for curing. That ridge is the secret to getting a great join that is invisible after it is sanded down. I have been using this method for a while and has cut down considerably on using putty. Some models I have built needed no filler at all using this method but depending on the model, using putty is sometimes inevitable.

I'm new at this so others may have thought of this but I found that if I glue the fuselage halves an inch or so at a time, I can make fine adjustments to the seam as I go along.  I typically start at the top of the tail and glue an inch or so at a time working toward the front of the plane.  After one section sets, I then align the next section, glue and let it dry and then repeat. I work toward an opening so I can work from both the inside and outside to get the final alignments as close as possible.  Its surprising how much wiggle room you have after much of the fuselage is glued.  It doesn't get rid of gaps, but does cut down on the step type of mis-fits.

Have fun,

Tom

I use several methods, one is aligning the halves and glueing them in sections so I can bend and shape the seam to limit the amount of sanding needed. I use Tamiya xtra thin so when the two halves are pressed together some plastic oozes out the seam facilitating seam cleanup. Sometimes I will sand the seam flat, other times I will apply some filler and then sand. This works well on models with recessed seams. However the Revell A-10 im currently working on has raised details and panels so Im finding it hard to smooth without ruining the details.

If you are using thin CA, it is important to get the edge of the fuselage halves perpendicular, so they do not meet in a V, but actually come together perfectly.  If the sides do not have locating pins, you can put down a full sheet of sandpaper on a flat surface and rub the sides each around on that. If the sides do have locating pins, you can sand the side that has holes, rather than pins, and use fine needle files on the areas between pins, carefully so that you take off a minimal amount of plastic.  Remember, thin CA does not fill gaps.

ROFL... resurrected a two year old thread...