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Tips on sanding leading edges?

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  • Member since
    June, 2016
Tips on sanding leading edges?
Posted by Murphy's Law on Tuesday, June 13, 2017 11:06 AM

Anyone have any tips or neat tools for sanding leading edges or fusalage seams? I use foam sanding sticsk or by hand and always seem to get flat spots especially around the leading edges of wings.

Thanks... Stefan

  • Member since
    December, 2013
  • From: Orlando Florida
Posted by route62 on Tuesday, June 13, 2017 11:41 AM

I try to avoid sanding seams as much as possible but some seams I cant avoid it.  When gluing halfs of anything together, I do my best to line up the parts as best as possible, clamp, hold, tape the parts together, and then apply the glue.  This tends to reduce how much sanding and filling that will be needed.

In the case of gluing two plastic parts together, when the parts are lined up, I apply a thin styrene glue, like tamiya extra thin or something similar.  As the glue begins to melt i slightly press the two halfs together.  This will press a thin bead of the melted plastic out and tends to fill in almost all small gaps. Once the glue and plastic are dry,  I go back and lightly scrape with an exacto blade and/or sand away the ridge that has formed.  

this keeps me from having to aggressively sand and avoids flat spots.

When it comes to larger gaps, I first try to see if I can add a plastic shim to the gap.  It is easier to fill larger gaps with shims that will fuse with the part and not shrink.  If this has not eliminated the gap completely, then comes filler.  

When I have to use filler, I try first to get the gap small enough with shims that a liquid type filler will do the job rather then a paste type.  My preference is mr surfacer in 500 and 1000.  I also have thinned paste puttys to a more liquid state.

I brush in the liquid filler, wait for it to dry, then swipe with a cotton bud slightly dampened with the appropriate thinner that will rewet and smooth out the liquid filler.  This usually takes 2-3 applications of brushing in the filler and then swiping with the cotton bud due to shrinkage and air bubbles.  this works very well on where the wing meet the fusalage.

This technique saves all the surface detail and only very light sanding if any is required with 800 or higher grit paper.  I can then go in and scribe any lines that were filled in if needed.

I find most puddy type fillers either dry too fast to work well or dry too hard and you have to sand with aggressive grits like 300-400 grit paper which makes for more sanding and repairing the surrounding plastic not to mention all the lost detail.  

If I do have to go to a putty, I will squeeze some out on a mixing pallet and then mix with the appropriate thinner to extend the dry time and soften it enough that it is more like a gel or toothpaste consistancy.  I find this works into the gaps easier and i have to use far less.  When it is time to sand, this thinner putty does not require aggressive sand paper.  I find I can start with 600 or 800 grit so it does not damage the plastic as much.

I also will tape off the areas near the gap i am filling with putty if I know I will have to sand it once dry to try and preserve as much of the detail as I can. 

  • Member since
    April, 2013
Posted by KnightTemplar5150 on Tuesday, June 13, 2017 5:20 PM

You might want to consider a Flex-I-File, Stefan. It's a simple C-frame that holds a strip of sandpaper which follows airfoils and compound curves very nicely. The starter set is reasonably priced and was a good addition to my tool kit. It's never left a flat spot for me to fix.

http://www.flex-i-file.com/flex-i-file.php

  • Member since
    December, 2002
  • From: Bury St Edmunds, Suffolk, England
Posted by Bish on Wednesday, June 14, 2017 12:59 AM

KnightTemplar5150

You might want to consider a Flex-I-File, Stefan. It's a simple C-frame that holds a strip of sandpaper which follows airfoils and compound curves very nicely. The starter set is reasonably priced and was a good addition to my tool kit. It's never left a flat spot for me to fix.

http://www.flex-i-file.com/flex-i-file.php

 

Thats what i use as well, great piece of kit.

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On the bench: Hasegawa 1/32nd Ju 87G-2

  • Member since
    September, 2006
  • From: Bethlehem PA
Posted by the Baron on Wednesday, June 14, 2017 11:30 AM

KnightTemplar5150

You might want to consider a Flex-I-File, Stefan. It's a simple C-frame that holds a strip of sandpaper which follows airfoils and compound curves very nicely. The starter set is reasonably priced and was a good addition to my tool kit. It's never left a flat spot for me to fix.

http://www.flex-i-file.com/flex-i-file.php

 
I second that.  I finally bought a Flex-i-file for just this kind of work, and for sanding mold seams on figures.  I always tried to sand seams like those, free-hand, using scraps of sandpaper folded up, cut in strips, but I could not get consistent pressure applied right to the point where it was needed.  The Flex-i-file allows doing just that.  It's another tool I wish I had bought years before.

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  • Member since
    June, 2016
Posted by Murphy's Law on Wednesday, June 14, 2017 1:03 PM
Well that settles it, I just ordered a flex-I-file off Amazon. Thanks for the input guys... Stefan
  • Member since
    March, 2017
Posted by Lord Voyager on Wednesday, June 14, 2017 1:58 PM

If you can't get a flexifile, I take a pipe of styrene cut down the middle and push my sandpaper into there... It works great and no flat edges at all. 

"The Grid. A digital frontier. I tried to picture clusters of information as they moved through the computer. What do they like? Ships, motorcycles. Were the circuits like freeways? I kept dreaming of a world I thought I’d never see. And then, one day… I got in.

  • Member since
    November, 2008
  • From: Florida
Posted by plasticjunkie on Wednesday, June 14, 2017 7:36 PM

I just follow the contour even if it's a slight curve and lightly sand with my padded sticks. I learned this method in woodworking when sanding curved wood pieces.

I've heard great things about the Flex a File tool so it's worth a try.

  • Member since
    November, 2009
  • From: Twin Cities of Minnesota
Posted by Don Stauffer on Thursday, June 15, 2017 9:03 AM

If the joint is not too bad I double a piece of sandpaper, hold it in the palm of my hand, press it against the edge, and go back and forth spanwise.  The paper wants to generally follow the LE curve.  Avoid sanding blocks or any stiff backing. If there is a bad mismatch, or a really bad joint, I use needle files, and indeed with those you need to watch to prevent flat spots.

 

Don Stauffer in Minnesota

  • Member since
    January, 2014
Posted by Silver on Sunday, July 16, 2017 4:06 PM

Add very thin round plastic o the leading edge and on top and bottom seams.Then your sanding will be better and the seams will go away.Sand lightly.Heated stretched sprue Works well.Glue in place.

  • Member since
    November, 2009
  • From: Twin Cities of Minnesota
Posted by Don Stauffer on Monday, July 17, 2017 8:45 AM

I should have mentioned that I often scrape a seam if it is really bad.  I scrape the seam to rough shape and then use sandpaper or files to finish it off.

Scraping is an old art of cabinet makers and machinists where you hold a blade tool with the blade almost ninety degrees to the surface and then pull it along the surface. It is hard on edges of blades, so I keep one of those X-acto blades where the blade makes about a 45 degree angle to the knife axis, rather than the acute angle of the #11 blade.  There is even one X-acto blade that has the edge and a 90 degree angle but those blades are harder to come by, and I find the 45 degree ones work well.

 

Don Stauffer in Minnesota

  • Member since
    January, 2014
Posted by Silver on Monday, July 17, 2017 10:40 AM

Scrape a seam is dangerous and can cause deep impressions.Use a sanding belt stick or board type.Work it slowly.

  • Member since
    November, 2009
  • From: Twin Cities of Minnesota
Posted by Don Stauffer on Tuesday, July 18, 2017 9:13 AM

Yes, scraping can take off plastic very fast.  On the other hand, that is one advantage on a really bad seam. I should have recommended practicing scraping on scrap parts before you use it on a good model.  Like any technique, you need to acquire the skill, but like most manual skills, once you learn it it will stay with you.

Don Stauffer in Minnesota

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