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Old Aug 06, 2012, 08:47 PM
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Fred's Secret Sauce.....

Not such a big secret, but when I have covered this before more questions came up than expected. This time I will include some photos to help 'show and tell' in case some of you want to try this. I do this on my foam builds often when there is no covering or other coatings involved.

Basicly, a Filler, primer coat, all-in-one, that doesn't weigh much but works really well. When many have been amazed at my finished airframes, this was the process I used. Let us go in sequence, and the photos are in order too.

1). I take some light weight spackle, and put a nice size plug in a little mixing bowl. This time my plug of filler is about the size of a hazel nut.

2). Next add some Polycrylic clear varnish (water based of course), about the same volume as the plug of light weight spackle.

3). Get some Talc Powder. I find it in Baby Powder, Foot Powder, but the Baby kind smells best. Watchout because many powders are Corn Starch, which we don't want! Talc is the magic that made balsa filler work in the old days of tissue and dope finishes. It is very fine and does a great job of getting those tiny imperfections filled, but sands away nice. Note the 'pile' of powder about equals the volume of the light weight plug we used too!

4). Add a couple-three drops of acrylic paint (craft paint, water based), and it can be white paint, but often I use a color to see the work in process and the finished results show up better. Use a color that works for your intended top coat. Light for light topcoats, gray for everything else! I usually use Yellow in the primer if I am painting Yellow top coats, because Yellow (and Reds) don't always cover well.

5). Now mix it well, it is very thick, but get it creamy and all one color and texture, working out any chunks. Now add water until it is like very thin whipping cream, thin shaving cream, or even thinner like a very thick paint. Brush this on your pre-sanded foam, making sure to completely wet everything and force mixture into any hollows, dings, scratches, etc.

Let this dry. Then we will sand it all with some 180 grit, and 220 grit papers, mounted to some sheets of beaded white foam. The foam sanding blocks are flat, but 'give enough' to not cause grooves and scaring. Just make sure to remove sanding ust often and use a reasonable pressure while sanding.

When you have sanded most of this formula away, you will see original foam, but many areas of filled and flush mixture, and the surface will be very smooth. Little weight gain, yet ready for top coating with paint. You can sand with even finer papers, depending on what top coat paint you will be using. This is good enough using craft paints, but if you will spray with Model Master or Tamya paints, I wold go to like 320 or 400 grit paper. All three kinds of paint work well with this process.

Last photo is a sample of using this filler/primer on a fff airplane I built, a Russian MiG-3. How appropriate, another Russian Plane.

Fred



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Old Aug 06, 2012, 08:53 PM
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Example #1, The vertical Fin pre treatment, was 0.6g. Filled, sanded, ready for top coat, 0.7g. We added a whole 0.1g (1/10 of a gram). Not bad, and it takes less paint to top coat once filled and sealed like this.

Fred




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Old Aug 06, 2012, 08:56 PM
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Example #2, the horizontal Stab and elevators was 2.1g. Now that it was filled/primed, sanded and ready for paint, we gained 0.2g.

Fred



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Old Aug 06, 2012, 09:39 PM
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NOW ya tell me how to do this after all of the issues I've had!!!......VERY nice MiG-3!!!...My problem is that I like to wet sand for the best finish...All of this water based stuff doesn't like to be wet sanded when cured so I've discovered...Even when topcoated with a commercial primer due to the primer being somewhat porous when sanded very thin, the primer absorbs water ruining the finish underneath...

I've found out that the best method is to sand dry, gradually working to finer grits...This clogs the sandpaper more easily as you go through more sheets dry sanding than when wet sanding...But I can live with that......

Still learning!!!...Kevin
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Old Aug 06, 2012, 10:31 PM
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Fred,

Thanks once again for another great thread. I really appreciate your sharing how you do things - very "educational".

Gene K
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Old Aug 06, 2012, 11:01 PM
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Quote:
Originally Posted by Kevin Greene View Post
I've found out that the best method is to sand dry, gradually working to finer grits...This clogs the sandpaper more easily as you go through more sheets dry sanding than when wet sanding...But I can live with that......

Still learning!!!...Kevin




Kevin,

I go through a lot of sandpaper, but it takes me a long, long, time! LOL. I use it until it falls apart in my dirty little fingers. The sanding blocks stop working months before I change them. Go figure, I am still learning too!

Fred



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Fred,

Thanks once again for another great thread. I really appreciate your sharing how you do things - very "educational".

Gene K




Thank you Gene.

I keep doing these threads because of the people like you that appreciate all the time involved and tell me it helps. I have noticed more and more, others are taking a bit more time to detail the small things, and I really like that too! Kevin is doing that with his T-45 Hawk build! We all need to share and learn from each other. I think over the years, I have re-invented the wheel at least 1,000 times. Maybe we can all help each other move forward without everyone re-inventing everything. Think what we could do if we already knew everything......... like our wives! (boy that would be trouble, I'm sure).

Fred
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Old Aug 06, 2012, 11:20 PM
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Dinner was awsome, but I wanted to put up another little test I did with the filler. I took the scrap pink foam piece you see, and it measured 8g, with a semi-smooth sanding job, no filler. Then I painted it quite liberal, on two sides, and measured it wet! Yes wet, it had grown 2.1g, but you can see the coverage with the filler/primer. Scale shows 10.1g

I let it dry pretty good, then sanded with the 180 grit, then 220 grit papers. I didn't get too fussy, just gave it a good sanding and weighed it again. Dry and sanded I gained 0.7g, and the scale shows the 8.7 reading.

So I ask you to click on (to enlarge) photo #1, then Photo #4. In Photo #1, you can note heavy sanding tore little gouges and the surface is pretty rough. Photo #4, after filling shows all that damage is filled and now smooth. I never fill this rough of a surface, so weight gain might be a bit much. Filling an already fairly smooth surface does help. Foam has some surface pores, hair, and other things that sanding leaves. This process repairs all of them pretty much.

So what does all this really mean? Heck if I know! At least we know the filler/primer is pretty light, works well, etc, etc, blah, blah, blah. I am betting my airplane will weigh exactly...... what it weighs when done, and I am not going to worry too much because I am doing the best I can! LOL.

I did something else cool today, and I will find out if it is going to work out really cool as I'm thinking it will, later. It's late enough I am done for today, and will have to post more tomorrow!

Fred




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Old Aug 07, 2012, 12:28 AM
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THANKS Fred for the tips!!!...Here are are a couple of picsof my T-45 ready for paint...I guess that the strange marks on the plane in these pics are from fingerprints left over from dry sanding...I definately went with a heavier method than you did...

Kevin
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Old Aug 07, 2012, 10:46 AM
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Quote:
Originally Posted by Kevin Greene View Post
THANKS Fred for the tips!!!...Here are are a couple of picsof my T-45 ready for paint...I guess that the strange marks on the plane in these pics are from fingerprints left over from dry sanding...I definately went with a heavier method than you did...

Kevin
Who cares if it is heavier! Looks way too great BTW. We all have our methods and if they work we should use them, because just look at your results! Love it, and thanks for sharing.

Fred
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Old Aug 07, 2012, 02:04 PM
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Who cares if it is heavier! Looks way too great BTW. We all have our methods and if they work we should use them, because just look at your results! Love it, and thanks for sharing.

Fred
Your way is definately lighter and gives the results we need which is to seal the foam for paint...I'm definately going with your method on the next plane...My sister is in from North Carolina and is coming over this evening for dinner, also bringing me a fresh supply of Depron!!!...

Speaking of dinner---We both like to cook--I'm making one of my signature grilled dishes tonight...Do you care if I post a pic when done???......

Kevin
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Old Aug 07, 2012, 04:19 PM
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Kevin, sure! I say yum yum! My sister-in-law (my fav) is from North Carolina too!


Now I had an idea that I am sure isn't new, but I needed to trim the wings to fit the shape of the fuselage side profile, plus have them at the dihedral angle of 5 degrees. This is a compound cut, and would be hard to sand into the foam and remain accurate.

So first the shape to fit the fuselage. Cut a manila folder to wing root cord width, and then cut and fit it to the fuselage profile. This was as easy as noting the gap fore and aft in the papers edge when held against the fuselage. Then I took a french curve and drew some curves inset by the gap distance. It took only one try, and one small secondary skive with the scissors.

Transfered this profile shape to some aluminum flashing stock. I made the flashing 1.5" wide, and about 3/4" longer on each end, and had them both trimmed the same size and shape. Not to critical, but at least equal enough to keep this concentric.Note layout marks on flashing, as it blends into and out of the template where the wing profile goes. Took scissors and cut out the curved profile shape. Layed the first one over the second, marked and repeated the cut.

Fred




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Old Aug 07, 2012, 04:28 PM
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A lot is going on in the first photo. Both aluminum templates were clamped together, and a 1/8" diameter hole drilled on each end, outside where the wing would go.

Sawed off two blocks from a piece of 3/4" pine, that measued 1 1/2" wide. Made these blocks 1 1/2" wide so they are a square shape. Drilled a 1/8" diameter hole through the block, top to bottom. I used a drill press so they would be straight and perpindicular.

Also made four pain stirring stick pieces 1 1/2" long, same 1/8" dia hole. Now you can see some 1/8" dia. dowel was used as pins to make a sandwich so the templates are aligned top and bottom, but seperated by the wood.

Fred




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Old Aug 07, 2012, 04:31 PM
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Note I used flat head screws so they would be flush with the wood. I took a Sharpie Marker and labled everything both sides to make it pretty goof free and so later our memory will be clear on setup and use.

Fred






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Old Aug 07, 2012, 04:44 PM
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Next I took some scrap foam sheet that is roughly 1/4" wide. I used fff, but 6mm Depron or other will work. Just think cheap, easy, and quick. This is just a tooling aide.

The 1/4" fff foam was made into a panel that is 1/4" wider than my wing, but will fit inbetween the wood blocks on my template sandwich. I made four, 5 degree angled triangles, and glued these to the panel. Note triangles are not all the way to a sharp point, so that they will cause some raised effet to my tooling top plate.

Speaking of which, a gued a top plate on top of the triangles. Look close and I did glue some short 2mm bamboo skewers on sides where the top extends or say overhangs, so I won't get any flexing or weakness (it's just foam!).

Flipped over you can see the overhang better. I then took a photo of a mockup of my idea of how wing will mount in template sandwich, on top of the 5 degree platform, for cutting the compound angles and curves.

Fred




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Old Aug 07, 2012, 04:53 PM
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So let's cut these wing roots cut. Pictures are worth a thousand words. Now is why it is nice to have your template sandwich nice and square. I overhong the wings about 1/16" just to get a clean and complete cut. Note the wing root is square to the templates.

Wing sits on the 5 degree dihedral ramp. Now I pass the hot wire across both templates at the same time. Done! Now we just have to flip the template block over to cut the opposite side wing panel (left and rights).

Pretty clean and accurate. No dirty words needed during this process to get it to work right either.

Fred




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