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Eliminating seam lines

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  • Member since
    September 2020
  • From: UK
Eliminating seam lines
Posted by CliveEH on Thursday, November 19, 2020 6:20 AM

Hi all

i'm having real problems eliminating seam lines particularly on aircraft where the 2 halves are glued together. Tried everything. I've glued so as to leave a small ridge when squeezed so it can be sanded across the join. I've graduated the sanding from coarser to fine and then polished. I've got, and used, Mr Surfacer 500 & 1200, Tamiya Putty white and Vallejo plastic Putty. Even tried glue + sprue. All the gear and no idea! My P51 Mustang has an intermittent line before and behind the cockpit with only the primer applied. A metallic  coat will show it off nicely. Always struggle with this but a particular issue with this kit - a 1/72 Airfix kit - if this helps.  Thank you for any guidance   Clive

  • Member since
    April 2020
Posted by Eaglecash867 on Thursday, November 19, 2020 8:20 AM

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.  

"You can have my illegal fireworks when you pry them from my cold, dead fingers...which are...over there somewhere."

  • Member since
    November 2009
  • From: Twin Cities of Minnesota
Posted by Don Stauffer on Thursday, November 19, 2020 9:25 AM

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 Stauffer in Minnesota

  • Member since
    October 2019
  • From: New Braunfels, Texas
Posted by Tanker-Builder on Thursday, November 19, 2020 11:23 AM

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.

  • Member since
    October 2019
  • From: New Braunfels, Texas
Posted by Tanker-Builder on Thursday, November 19, 2020 11:27 AM

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. 

  • Member since
    July 2013
Posted by steve5 on Thursday, November 19, 2020 2:44 PM

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

 

  • Member since
    September 2020
  • From: UK
Posted by CliveEH on Thursday, November 19, 2020 5:41 PM

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. 

  • Member since
    September 2020
  • From: UK
Posted by CliveEH on Thursday, November 19, 2020 6:00 PM

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 

  • Member since
    September 2020
  • From: UK
Posted by CliveEH on Thursday, November 19, 2020 6:47 PM

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. 

  • Member since
    April 2020
Posted by Eaglecash867 on Thursday, November 19, 2020 6:52 PM

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. 

 

 
No problem CliveEH.  Rescribing is easy with super glue since its essentially liquid plastic.  Once hardened, it behaves just like styrene.

"You can have my illegal fireworks when you pry them from my cold, dead fingers...which are...over there somewhere."

  • Member since
    May 2011
  • From: Honolulu, Hawaii
Posted by Real G on Thursday, November 19, 2020 9:32 PM

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.

“Ya ya ya, unicorn papoi!”

  • Member since
    June 2017
Posted by Chemteacher on Friday, November 20, 2020 5:33 PM
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.

On the bench: Revell-USS Arizona; Airfix 1/72 P-40B

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