Author Topic: How do you glue a straight strip of wood to a curve?  (Read 2436 times)

Happy Days

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How do you glue a straight strip of wood to a curve?
« on: October 01, 2015, 17:32:23 PM »
Sticking two straight lengths of wood together doesn't require much thinking about. But often in the interests of aerodynamic efficiency the
 construction of a model aeroplane requires the creating of
 curves or radius's.

So how do you make a piece of wood that wants to remain straight, bend?  :?: Well you could try steaming it! That's a lot of work, so here's  a simpler way.

The following is a picture of the inside of the fuse of a Phase 6 while it's being built. Sorry about the strange angle of the photo, it was the only way
 I could get it all in shot.


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 You can see the top and bottom forward section (to the left of the picture) of the fuse has a radius.
(Ignore the little 'hook' looking part at the nose, and ignore the lines I've drawn on the fuse as well. They're just position markers.)



The instructions tell me that I have to secure a couple of pieces of triangular section strips to the top and bottom edges of the fuse.
Although I'm using triangular section the same principle would apply to whatever shape you happen to be using.


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The classic method of holding pieces of wood in place while the glue cures is to use pins. Whenever I've tried that I usually found that the pins end up
 splitting the pieces of wood I was trying to hold together, thereby not solving a problem but in fact creating an even bigger one!

I don't claim to have 'invented' the following solution, I am merely passing on what I have found to work best.

So firstly, let's mark what will be the inside radius of the strip of wood with small marks about every 20mm.



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Secondly we'll cut some slots into the strip of wood about half way through it's thickness at the points previously marked.



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When finished the strip of wood is now able to be bent, so it can match the curve of the side panel of the fuse.



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Now we come to the sticky bit. (Sorry, that should read, 'Tricky' bit.) Run a broken line of (in this case) white PVA glue along the edge of the fuse where the
 strip of wood is going to lay. (It looks like a load of Morse code dots & dashes doesn't it)


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Ensuring we have some thin CA glue and aviator (kicker to our American friends) to hand  we get ready to lay the triangular section in place.


Start by placing the end of the wood strip in place and get it to stay there with a drop of CA glue. If need be, spray a little activator on the CA to cure it quickly...........


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As you bend the strip of wood and push it into place you'll see the white PVA ooze out. Where there isn't any white PVA oozing out put another drop of CA. Hold it there till the CA cures, (Again speed the process up a little by spraying the CA with activator.) In the next picture you'll see that I spilt an extra drop of CA...........silly Keithy!  :oops:


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Keep repeating the process until the job is completed. Finally rub some PVA into the slots that were cut in the wood strip to return it's strength.  Job done! And no split timbers.

You might ask, why use PVA? Why not use CA glue throughout?
Well,....one reason is cost. Another is weight, (Cured CA is heavier that cures PVA) And a third reason is that CA forms a very brittle joint, where as PVA has a little bit of 'give' in it. :D

Little Keith
Try not to run out of airspeed, altitude and ideas....... all at the same time.