On Feb 15, 7:55*am, Brian Whatcott wrote:
I bought a tube drilling jig, to make those
nicely fitted tube joints at 90deg, 45 deg etc....and plenty of other
things too.
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Funny(?) Story:
Until Harbor Freight came along I've seen tube-drilling jigs in use
perhaps half a dozen times in my life. All but one of those times was
at the shop of a sub-contractor and the tube-drilling jig was usually
home-made. AFTER Harbor Freight came along I've guess I've seen a
dozen or more of the HF tool, always rigged to a DRILL PRESS.

The funny part of this tale is that, until the Harbor Freight drill-
jig came along, the drill-jig was ALWAYS fastened to one corner of a
WORK TABLE, providing room to support the tubing, which on the first
cut, could be up to twenty feet long. Power was provided by a 1/2"
drill-motor.

Personally, I've got four or five round files from 3/8th to 3/4", all
that's needed to put a fish-mouth on a piece of tubing that is going
to be welded. (You can cut a large fish-mouth with a file of smaller
diameter.)

The tricky bit in hand-filing a fish-mouth is HOLDING the tubing so
that the fish-mouth is perfectly aligned with the fish-mouth on the
OPPOSITE end of the tube. The holders are hunks of MAPLE, drilled to
match the diameter of the tube. This allows the piece of tubing to be
held in a vise and adjusted so as to facilitate the filing, which is
always done two-handed with the file perfectly level (or nearly so).
A machinist's protractor is used to verify the position of the
tubing. Snips or an angle-head grinder is used to notch the fish-
mount, reducing the amount of filing needed. A short piece of tubing
matching the size of the fish-mouth is used as a gauge.

As-received tubing is usually oily. The oil is removed to ensure the
clamps can get a grip. When the clamps can no longer get a grip you
can 'tighten' them by pressing them against a disk sander for a
moment. You may also add rosin to the tubing groove.

The sides of most fuselages fabricated from welded steel tubing are
identical, allowing you to cut TWO pieces. The longerons are
typically supported on two to four saw-horses and the side pieces (ie,
vertical & diagonal tubes) are tack-welded as soon as the tube(s) are
cut. The pieces for the top & bottom may not be symmetrical so that
tacking only one at a time (ie, either the top or the bottom) is
usually the most practical method. Once all of the structural member
for the fuselage have been fitted and tack-welded, you will probably
find it more convenient to support the fuselage in a rotisserie,
allowing you to ROLL the fuselage as you finish-weld the tacked
joints. Using only the tools described here it takes 35 to 40 man-
hours to put the typical fuselage on its gear. Then comes all the
fiddley bits; tabs for fasteners; fuel tank supports, controls and so
forth... which can take an additional 100 hours or more (!!).

Oddly enough, when you see an ad for an AIRCRAFT WELDER, odds are
they don't want someone who only experience is fuselage structures.
What they usually want is someone experienced (usually certified) in
welding aluminum, monel and so forth. (As a point of interest, the
last time I checked [1970's] there were more than a hundred
certificates that applied to AVIATION/AERO-SPACE welding. If you
have a lot of experience (and the certificates to go with it) some
companies will hire you as a 'weldor under instruction' giving you 90
days (or whatever) to gain the experience needed to pass the
certification test needed for their particular application.

Of course, that was then. Nowadays you'll find it kinda hard to
compete with a fully certified Chinese weldor pulling down $17 per
week... (They save so much on LABOR they can afford to have the
parts FLOWN from China to the USA)

On larger diameter tubing having a heavier wall, an angle-head
GRINDER is usually more convenient than filing, especially if you have
that program (WINTUBE ?) that prints out a pattern of the cut after
you enter the diameter of the tubing, the angle of it's intersection,
and the diameter of the tube it's supposed to mate with. (This is
very handy for fabricating roll-cages and the like for vehicles that
operate off pavement.)
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I would not dream of putting a
machine lathe in an unheated workshop where the ways might attract a
layer of rust.
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So buy a Flit gun and 5 gallons of kerosene. After using the lathe,
pump up the Flit gun and give the lathe a light coating of kerosene,
then cover it with a piece of canvas that is NOT allowed to touch any
unpainted surface.

-Bob

PS -- Can't find a Flit gun? Then use one of those refillable aerosol
cans... or use an air-brush.