Making Blowpipes
=How to Make a Bench Gas Blowpipe.=--The blowpipe illustrated by Fig. 67
gives a powerful flame. It can be clamped to the edge of the workbench
by means of a winged nut, a hole being made near the edge of the bench
to accommodate the bolt. A piece of hard wood A, 5 in. by 2 in. by 1 in.
thick, has a strong iron bolt B passed through at one end. A 2-in. cube
C, which should also be of good hard wood, is screwed firmly to the
other end of A, the combined block being perforated through the centre
to take a length of gas tube D, which carries a gas-bracket with flange,
elbow joint, and tap E. The flange should be screwed down to the top of
the block. The elbow joint allows the direction of the flame to be
adjusted within a wide range movement. The arm of the bracket is
removed, and a shorter tube F, 3 in. long, is substituted. This carries
a 1/2-in. iron [T]-piece G. The tube H, which is 3 in. long, should be
of brass, threaded at one end to fit into the [T].
[Illustration: Fig. 67.--Bench Gas Blowpipe]
The air is conveyed through an 8-in. brass tube J 1/4 in. in diameter,
which should be smooth inside. This latter point is of some importance,
and, if preferred, a glass tube may be used instead of brass, the
current of cold air having a sufficient cooling effect to prevent undue
heating. The end should be cut off sharp with a file in the ordinary way
and left in that condition. Smoothing the edge by fusion in a flame will
not improve matters, but rather the reverse. Of course, the other end,
which comes outside, must be smoothed to prevent injury to the
indiarubber tube used for making connection with the bellows. The air
tube must be held firmly in the centre of the gas tube, while capable of
being moved in or out for the purpose of adjusting the flame. This can
be done quite satisfactorily by means of a short brass tube or nipple K,
threaded to screw into the [T] (_see_ Fig. 67). A sound cork should be
driven into this short tube so as to entirely fill it, a hole being made
with a cork-borer to admit the air tube. This hole must be exactly
central, and the cork must grip rather tightly.
A foot-bellows is generally used for supplying the air, the bellows
being connected with the air jet J by means of an indiarubber tube. The
tube D, which should extend an inch or so below the bench, is to be
connected with the gas supply.
=A Simple Gas Blowpipe.=--A simple form of gas blowpipe is shown in Fig.
68, the rubber tube connecting it with the gas supply being fixed on the
pipe at the point of connection with the cock. To construct the
appliance, one end of a piece of brass gas pipe of the required length
with, say, a 3/8-in. bore, is bent as shown, whilst at the back of the
curve thus made a hole is drilled to admit a tube A 5/16 in. in
diameter. This should have one end (_see_ dotted lines) bent to
correspond with the angle previously formed in the larger tube, whilst
its other extremity should be bent upwards. Make these pipes red hot
where they are to be bent, and, if they are afterwards plunged in cold
water, the material will to some extent be softened, and its tendency to
split will be obviated. The smaller tube is passed through the hole in
the bend of the larger one, the ends being almost flush and quite
concentric. Solder the parallel portions of the tubes together, and then
fix a gas-regulating cock to the larger one, as in Fig. 68. The end is
then connected to an ordinary bracket or burner by means of an
indiarubber tube G, and a short piece of tubing is fitted with a bone or
other mouthpiece, and attached to the projecting end of the air tube.
This instrument will do any soldering, and will be suitable for melting
gold, silver, and brass, or brazing odd jobs in iron or steel. Of
course, when used for the last-named purpose it would be in conjunction
with asbestos tubes or other supports.
[Illustration: Fig. 68.--Simple Form of Gas Blowpipe]
[Illustration: Fig. 69.--Larger and more efficient Blowpipe]
=Proportion of Air to Gas.=--As regards the relative volumes of gas and
air for blowpipes, the late Mr. Thomas Fletcher said that, speaking
roughly, but still sufficiently near to make a correct rule by which to
work, a blowpipe requires one volume of gas to eight of air. If the gas
is supplied at a pressure equal to 1 in. of water, and the air at eight
times that pressure, then, to get the best effect, the area of the gas
and air pipes should be equal. If the air supply is equal to 16 in. of
water pressure, the gas pipe must be double the area of the air, and so
on in proportion. Some makers assert that a better working flame is
produced by using ten volumes of air to one volume of gas; but, of
course, if the blowpipe is fitted with taps, the supplies can be
adjusted easily. It will be found, however, that any practical departure
from Fletcher’s rule will result in a loss of power.
=Capacities of Blowpipes.=--It has been said, a blowpipe with a 1/8-in.
air jet, if worked with an air pressure of 10 oz. per square inch--that
is, 15 in. of water--will braze up to about 1/2 lb. total weight; or in
other words, will securely unite two pieces of brass each weighing 1/4
lb. With the same pressure a 1/4-in. bore air-jet will braze a total
weight of about 2 lb., and so on in proportion. It will be understood
that the air jet is measured at the point at which the blast leaves the
air tube, whilst the area of the gas supply is that of the annular space
between the two tubes. When the air tube is thus carried inside the gas
tube (_see_ Fig. 69), the tool appears to be much larger than it really
is, and this accounts for the fact that a 1/2-in. size blowpipe with the
air tube fixed outside the gas supply is just as effective as one of the
3/4-in. size which carry the air tube inside the stem. All indiarubber
tubing must be perfectly smooth inside, for if it is wired or in any way
rough, the resultant friction will cause a loss of pressure. It should
also be of as large a bore as is convenient.
=Large and Efficient Blowpipe.=--A large and efficient blowpipe that can
be made in a few minutes is shown by Fig. 69, the only materials
required being a [T]-coupling and diminishing socket, an elbow, and one
or two pieces of pipe. The air tube A (represented for the most part by
dotted lines) passes through the diminishing socket until it almost
reaches the nozzle of the blowpipe, with which it is concentric. By
using the elbow D, the two supply pipes are brought parallel to each
other, so that the indiarubber connecting tubes can be more easily held
in the hand like reins, as by simply squeezing them the flame can be
readily regulated. Sometimes, in cases of emergency, a plug drilled to
meet the air tube is used in place of the socket. The plug is thrust
into the end of the [T]-socket; but in all cases it must be airtight.
This blowpipe can be used efficiently only in conjunction with a foot
blower.