On Sep 26, 2:43*pm, flybynightkarmarepair wrote:

http://users.lmi.net/~ryoung/2006/11...atch-builders-...

I find the use of a scrap of 1/4" softwood ply to be very, very
helpful in distributing the blows - NOT door skin, and NOT anything
any thicker - if it's too thick it'll form a hard spot at the edge of
the ply, and put kinks in.
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To All:

I'm remiss for failing to mention this technique which is often
referred to as 'dressing' the flange. As Ryan mentions -- and shows
in the photo -- dressing can produce a beautifully accurate flange and
is the standard method when an accurate flange -- of any length -- is
required. A good example of this would be the flanges on the aft
belly skin of the Teenie Two. But there are many cases where
dressing, while desirable, is NOT required, such as for the spar
flanges. Subsequent steps in which the wing skins are attached to the
flanges, will cause the uneveness of the flange to disappear,
submerged beneath the wing skins.

Some may think EVERY flange should be dressed but that is true for
every case. Dressing will produce a neat flange of uniform width but
it will also give you a bend that exactly matches the edge of whatever
you are using as your clamp. In the case of the Teenie Two spars, the
RADIUS of that bend should be at least an eighth of an inch or about
3T (T being the thickkness of the metal). This is because extrusions
will be nested INTO that bend. In order for the extruded angles to
nest properly their outside corner must be rounded off to match the
radius of the bend. If the radius of the bend is too large you will
remove too much metal from the extruded angles. Indeed, a bend radius
of 3T is pretty much the norm when forming a flange and for the Teenie
Two's spars that degree of precision is achieved by sanding or filing
the edge of your hold-down and then 'dressing' the metal against it.
But the hold-down used to produce a 3T flange in the 0.040" spar stock
would be inappropriate for the flanges on the aft-lower fuselage skin,
which is only 0.020" ...giving you a bend radius of 6T. For the .020"
skins you would need a different hold-down.

Metal hold-downs work best but forming the radius'd edge takes quite a
bit of work. Wood is much easier to work but is usually too soft to
form an accurate bend in heavy gauge aluminum. A good compromise is
to use DOOR SILL STOCK. This is usually made of Red Oak and comes in
lengths up to six feet.

An advantage of the Teenie Two over other metal airframes is that it
uses only TWO thicknesses of metal, .020 and .040. Some will argue
that this is inefficient, that using a variety of metal thicknesses
saves weight. And it does. About THREE POUNDS. The performance of
the Teenie Two and the number of them flying makes it clear that a
three pound penalty is acceptable.

-R.S.Hoover