Eliminating seam lines

I have never really been a fan of using putty for getting a complete, invisible filling of a seam.  What I found that works the first time, nearly every time (about 95% of the time), is super glue.  I put a drop or two of medium viscosity super glue on a sticky note, and then use a toothpick to transfer the glue to the seam a little bit at a time...just touching the toothpick to the model lightly (don't want to put it on in a spreading motion, just more like little dabs).  After that, I let the glue cure overnight.  After the glue is cured, I take a black sharpie and scribble along the beads of cured glue, making sure to force the ink into all of the tiny nooks and crannies on that bead of glue.  This serves as a leveling indicator.  After that, gently wet sand (preferably using running water) using progressively finer grits, following the contour of the joint until all of the black is gone.  You'll still be able to see the seam at this point because of the clarity of the super glue.  But, once you put primer on it to check the seam, it should now be invisible, even when the final paint or metal color goes on.  Sometimes you'll see the little, intermittent seam still visible.  For those, you just go back to the super glue and dab to touch those up and use the same sanding method.  It usually only takes one application, but sometimes you'll have to do the touch-up.  The beauty of using the super glue is that, as long as you don't spread it or mess with it after dabbing, it will only temporarily soften the primer but will form a permanent bond with it once cured.  No more taking the primer off when applying putty.  It also doesn't have the same tendancy to continue sucking up primer and paint like putty does, which sometimes leaves you with a visible seam that you'd swear wasn't there before.  It wasn't...the putty in the seam just continued to suck up primer and paint from underneath.  This is now my go-to method for invisible seams.  

This is an age old discussion in modeling.  Many, many ways to skin a cat.  Each time you do it the method to use may vary, depending on the seam.

There are different problems that a seam can give, depending on the particular kit and the specific seam.

The ideal condition is that the two sides of the seam are exactly parallel and the parts fit exactly.  Then, just the glue joint, properly smoothed is good enough that primer will hide it.  By parallel, I mean in both directions- along the seam and the walls of the seam.  There can be a gap because the two parts are not parallel along their length, or the walls of the seam are not parallel.  The later is the most common.

It is possible to make seams parallel in both directions by rubbing each part along a sheet of 240 or 150 grit laid on a perfectly flat surface.  If your benchtop is not flat enough, set aside a foot square block of MDF.

There are many ways to sand or smooth the seam after gluing or applying filler.  I rarely use sandpaper.  I prefer filing or scraping.  Very nice needle file sets are available that cut fast buy leave finer scratches than medium sandpaper.  Only problem is that styrene dust is hard to clean out of files, and though soft can dull the files in time.  I go through about two sets a year.

Scraping is very seldom discussed but is an excellent technique if you master the skill with a bit of practice.  Scraping is a centuries old skill used in carpentry and machining to get a flat, smooth surface.

I do scraping with a  hobby knife.  I keep one handle with a blade just for scraping.  It does dull the blade fast.  And, I use a blunt point blade, not a sharp angled one like an 11.  The blade is held at almost but not quite 90 degrees from surface, and about 90 to the direction of the seam.  The top of the blade should lean very slightly towards the direction of movement, and you move the blade along the seam.  It smooths well and with proper technique leaves no scratches in the surface, so no sanding is needed.

Try searching for "finish scraping."

Don; About your files;

       I have three sets. I started doing something that I saw in an old Mechanix Illustrated Magazine for large furniture files. I soak them in Lacquer thinner then scrub them with a Denture brush and a Baby's toothbrush. It's some work, but, will keep your expenses down In the file department.

Aha! Clive EH!

 One of the things I do is this. I wipe a real thin Sprue Glue over the outside of the seam. Then I put a medium thichness Sprue Glue down inside on the edges of the seam. A week of so later I go back and file it all smooth and because of it being plastic like the kit I can re-engrave panel lines easier. I do keep panel lines on the larger planes. And I omit them entirely on smaller ones. 

I'd forgotten about this , but sprue-goo , does a great job . was watching ISM ,and he was using it .

Thank you Eaglecash867. I'm going to try this now. Rescribing panel lines through super glue would be new to me but it shouldn't crumble in the same way that putty can. Thank you again. 

Thank you Don. I thought I was careful with the fit but I wasn't looking out for the points you made. Getting this right avoids lots of work later on that isn't always entirely successful. 

I'll try scraping. Always looking for something that reduces the need for putty. May be too late for this kit which is fast becoming a test piece.  I will get some decent needle files. 
Thank you again 

Thank you Tanker-Builder. Intuitively Sprue Glue should be ideal. Pouring a liquid made of the same material into a hole should work. I haven't used it as much as I should and never in the refined way you do. I'm not a novice but this area has always caused me a problem and tends to be glossed over on You Tube and mags or focusses on easy areas, not (for me) the dreaded centre join of aircraft fuselages. 

CliveEH

Thank you Eaglecash867. I'm going to try this now. Rescribing panel lines through super glue would be new to me but it shouldn't crumble in the same way that putty can. Thank you again. 

 

Gluing down stretched sprue on a seam works fast too.  I always use the sprue from the kit being worked on.  As others have mentioned, preparation of the join is important.  The more perfectly matched the halves are, the less work afterwards.

One benefit of the sprue method is that it practically eliminates ghost seams.  I build glacially slow, and some years-old seam lines are still completely invisible.  I usually used to suffer pesky ghost seams after priming/painting, as the paint seems to soften the putty ever so slightly, causing eventual shrinakge, but the sprue filled joins are still invisible.

Everyone has their own technique which works for them.

Mine starts with gluing the halfs together carefully. This mean taking the time to glue the section a little at a time. I will first glue the nose and hold firmly with my fingers until the it sets then move down to the fuselage again glue and hold, then to the tail. Even though it's only two pieces getting the allignment right and gluing the peices together as close as possible is a good starting point.

I will then use a hobbie knife and scrape the seams lightly to flatten it out.

Next I apply Tamiya Basic Putty with a toothpick or spatula. Let dry and sand. I repeate this step until I get the right amount of levelness on the seam. I will sand to a fine finish.

Lastly prior to paint, I will prime with Mr surfacer 1000 and check the seams once more. If there are gaps I will fix them with Tamiya putty sand and repeat the priming step.

One last note. If it's a particularly large gap. Putty will not work since it is soft and will break. In that case I will use Zap-a-gap super glue. Sand then apply putty.

Zap a Gap

Mr Surfacer

Tamiya Putty

I use Plast it Weld in a Touch N Flow applicator to get solid invisible joins and pin point application accuracy. The stuff will melt the plastic and once cured can be sanded smooth eliminating the use of putties. I rarely use putty creating a solid join since discovering this method. I squeeze the halves together to get the ridge and clamp the parts overnight then sand the ridge away leaving no trace of a join line.  Most important the halves have to be perfectly even having no step at the join line.

Speaking of putties, PPP is great and easy to work with but you must shoot clear gloss over it if metallic paint will be the topcoat otherwise the repaired area will be visible.

I cement things together a little at a time too, so I don't end up with one big joint trying to take all of the stress of two pieces that may not be perfectly mated here and there.  It makes it easier to work things around and make it look as if things actually fit together really well when they didn't.  Came across a YouTube video a few years ago that showed that technique, so its what I use now.  The video blew me away, because the guy was touching liquid cement into the joint...and then waiting about 30 seconds before pressing the joint closed.  I guess the closeness of the two pieces keeps the cement from evaporating too quickly and gives it time to work on melting the plastic.  I have my Squadron Tools seam scraper that I remove the bead with after letting it all harden for 24 hours.  Sometimes I still end up with a tiny gap here and there, and then I use the Super Glue/Sharpie method for making those go away.  For parts that were meant to go together and leave a visible panel line, I use snakes of Milliput and work those into the joint with a toothpick.  Then I use damp q-tips to smooth out the Milliput and remove the excess so I don't have to sand anything.

Chemteacher

I used Perfect Plastic Putty for the first time on my current build. It worked great with a lot less sanding and destruction of detail. It’s water soluble and cleans up great with a damp Q-tip or damp piece of paper towel.

No shrinkage?

disastermaster

 

 

Chemteacher

I used Perfect Plastic Putty for the first time on my current build. It worked great with a lot less sanding and destruction of detail. It’s water soluble and cleans up great with a damp Q-tip or damp piece of paper towel.

 

 

No shrinkage?

 

I have not found it to shrink up like Mr Surfacer

disastermaster

 

 

Chemteacher

I used Perfect Plastic Putty for the first time on my current build. It worked great with a lot less sanding and destruction of detail. It’s water soluble and cleans up great with a damp Q-tip or damp piece of paper towel.

 

 

No shrinkage?

 

None whatsoever 

disastermaster

 

 

Chemteacher

I used Perfect Plastic Putty for the first time on my current build. It worked great with a lot less sanding and destruction of detail. It’s water soluble and cleans up great with a damp Q-tip or damp piece of paper towel.

 

 

No shrinkage?

 

Just when I swim in cold water