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Flaring tubing in
preparation for mounting lampshades
basically, two different methods of flaring the end of a segment of our
stainless steel thin-wall tubing.
The first, is quite
simple and is applicable for our N2018 (0.018"
diameter) and N2025 (0.025" diameter) tubes. We refer
to this method as "cold flaring" because it is a one-step process that
does not require any annealing (softening) of the tubing end. The larger
diameter tubing (.032" diameter and larger) has a bigger material
cross-section, and typically thicker tubing wall which makes the cold
flaring process much more difficult. For these larger sizes, we first
anneal the tip-end of the tubing. Flaring is then, very easily
Once a tubing
segment has been cut to length and deburred, it can be flared.
The easiest way we've found so far is to slide a .012" support
wire into the tube with a slight bend in the wire so it will stay in position in
the tube. Clamp the tube firmly in a pin vise with the end of the tube
just protruding past the jaws of the pin vise (about 1-2 tube diameters or so).
Position the support wire slightly recessed from the end of the tube (maybe even
with the pin vise jaws or slightly farther in. Make sure the tube is tightly
clamped by the pin vise.
pin-vise vertically with the exposed tube end facing up. If a long
section of tubing is to be flared, we recommend using pin-vises made
by the L. S. Starrett Tool Company, because their pin-vises have
open ended jaws so the tubing can slide all the way through the vise
and out the back of the vise handle. Some cheaper pi-vises have
solid-backed jaws which don't allow material to be pushed in past
the jaw teeth.
We have found a
simple method of supporting the pin-vise in vertical position on the
workbench is the use a piece of metal (steel, aluminum, or brass)
with a hole drilled through near one end that the vise handle can
slide through and stop at the back of the vise head. Figures 1 and 2
below show the holding method.
Be sure the tubing is
tightened firmly in the jaws of the pin-vise. Even though the
smaller tubing is very thin-walled, it can be held tightly in the
vise without damaging (crushing) it.
Choose a carbide scribe,
compass scribe pin, dental pick point, small steel pin ground to a
tapered point, or even a ordinary straight pin. This will be your
Place the pointed tip into
the tubing end and tap firmly (but not too heavily handed) on the
back end. You may need to inspect and repeat tapping to get
the slight flare you want, but once you've done this one time, it
will be easy to repeat the process.
The amount of flare at
the end of the tube does not need to be very much.
When the lampshade is hole-punched with the correct size drill for
the tubing being used, the shade will fit very closely on the
tubing. Only a slight flare is needed to hold the shade in position
and the epoxying operation to hold these two parts together is where
all of the strength is achieved.
You will find that there is a
bit of trial and error when doing this operation. If you tap too
hard, the tubing will disappear down into the pin-vise. Not hard
enough, and the tubing won't flare enough. You may find that the
pin-vise jaws need to be tightened more to hold the tubing more
firmly. It is possible to over-tighten and cause some deformation of
the tube, but that requires very sever tightening in most cases.
After one tube has been flared, you will know the correct pin-vise
tightening and tapping that works for you.
Flaring annealed tubing:
Out stainless steel tubing is manufactured with a
heat treatment that gives it good hardness for structural durability
without being too hard and therefore brittle. Not quite spring
temper, but close. In the larger sizes, this makes it difficult to
flare as we need for mounting lampshades at tube ends. An easy way
around this problem is to fully anneal the very tip of the tube end,
which brings it to a dead-soft (for stainless steel) condition. Once
annealed it will certainly not be as soft as say, copper, but
certainly much softer than before and much easier to work with. The
reason we only anneal the very tip of the tube is so the rest
remains structurally as strong as possible for good durability.
If this method is being used
for flaring, we recommend that any tubing bending (for curved-neck
streetlights or gooseneck building lights) be performed
first and the annealing of the tubing tip be done
after bending. A pin-vise does not have to be used when
flaring annealed tubing, as you will see below.
The annealing process is very simple for the
flaring we will be doing, so we don't need fancy laboratory
annealing ovens or any such equipment. The only heat source required
will be an open flame such as a match, candle or small torch. Your
wife's gas range in the kitchen will also work fine but I suggest
that if that is your heat source, you wait until she is out
To anneal the tube end we heat the very end until
it glows a cherry-red color (just at the very tip only). Then, let
it cool to room temperature. That's it... it's all annealed! See figures
3 and 4 below.
Once the tubing has cooled,
it can be pulled through a piece of fine steel wool a few times to
remove the dark sooty appearance at the end.
The tubing can now be clamped
in a soft-jawed bench vise or any holding fixture that will keep it
steady on the workbench. It should be positioned so the tube end is
facing up and toward you.
As with the cold flaring
method above, a small straight pin or needle will be used, but
tapping on the pin or needle won't be necessary. The needle will be
placed into the end of the tube and a slight side-to-side and
front-to-back "prying" motion will distort the end of the tube into
a flared-like shape. See figure 5 below.
The purpose here is not to make a perfectly
symmetrical looking flare (horn-like shape), but to give the tube
end a fairly even flare that will keep the lampshade in position
while the epoxy placed on the rim of the flare on which the
lampshade is seated, can fully cure.
This completes the tubing flaring
© 2008 Ngineering