Metal Spinning 4

Metal Spinning 4

The scale, after annealing, should be pickled off in an acid bath

(described further on in this chapter), and the part thoroughly washed

in running water. Brass, German silver and the harder metals should be

hammered before annealing; it is not necessary to hammer zinc, copper,

aluminum, etc.

 

A pyrometer in an annealing furnace would be an advantage where

quantities of the softer metals such as zinc, aluminum, etc., are being

heated. Copper is annealed the same as brass and is also pickled. Zinc

is coated with oil before being put in the oven, and when the oil turns

brown, which occurs when the temperature is about 350 degrees, the

metal is ready to take out; it should then be plunged in water to shed

the scale, but not pickled. The melting point of zinc is 780 degrees

F. Aluminum can be annealed the same as zinc, as the melting point is

1,140 degrees F.

 

Steel should be annealed by heating to a cherry red and then allowing

it to cool slowly; it should be scaled in a special pickle, thoroughly

washed, and then put back in the fire long enough to evaporate every

particle of acid that may have remained from the pickling operation.

Any acid remaining on the steel will neutralize any lubricant that is

applied when spinning. Annealing should be avoided wherever possible.

Open hearth steel only should be used. It should be free from scale

and preferably cold rolled. Bessemer steel is not suitable, except

for very shallow spinnings. Tin plate made from open hearth steel can

be spun about one-half as deep as its diameter where the shape is not

too irregular. German silver is difficult to spin, especially when

it contains over 15 per cent nickel; it has to be hammered before

annealing, the same as brass, to avoid cracks.

 

 

Lubricants

 

Common yellow soap cut up in strips about ½ inch or ¾ inch square is a

good lubricant for spinning most metals. It should be applied evenly

to the disk or blank while it is revolving, by holding the soap in

the hand and drawing it across the surface. Beeswax is the best for

spinning steel, but it is expensive. Lard oil mixed with white lead is

a fair substitute. Either mutton or beef tallow applied with a cloth

swab is very good on most all metals; also vaseline and graphite mixed

to a paste and applied the same as tallow.

 

 

Examples of Spinning Various Metals

 

The different metals are malleable, ductile and tenacious in the

following order; white metal or britannia, aluminum, zinc, copper, low

brass, high brass, German silver, steel, tin plate. White metal does

not harden in spinning, but it requires special skill in handling, or

the metal will be of very uneven gage. The best metal for an amateur to

start on is copper, as it is both tenacious and ductile, and will stand

much abuse in the fire and on the lathe. One of the peculiar properties

of zinc is that it has a grain or texture, and when spinning, the two

sides that go through the rolls lengthwise will be longer than the

sides that have the cross grain, requiring the shell to be trimmed off

quite a distance to even the edge.

 

To show the possibilities of working the different metals, and their

relative spinning values, a number of articles made from different

materials are illustrated herewith.

 

[Illustration: Fig. 16. Zinc Lamp Shade Spun in One Operation without

Annealing]

 

A zinc lamp shade is shown in Fig. 16 that is 14¼ inches in diameter

and 4¾ inches deep. This shade was spun in one operation, without

annealing, from a flat circular blank. All zinc should be warmed before

spinning, either over a gas burner at the lathe or in hot soap water,

and the chuck also should be heated, as otherwise the blank will soon

chill, if spun on a cold metal chuck, as the chuck absorbs the heat

long before the operation is finished. Of course this does not apply

to wooden chucks. The chuck may be heated by using the burner shown in

Fig. 17, which is located around the spindle of the lathe. The size of

the burner should, of course, be in proportion to that of the chuck

used. The burner illustrated is 8 inches in diameter. It has several

small holes drilled for the gas on the side facing the chuck. The heat

of the chuck is regulated by varying the supply of gas to the burner.

The blank is heated before it is put on the chuck and the friction of

the spinning tool helps to keep it warm until it comes in contact with

the chuck. The metal retains its heat until the job is finished, and

this sometimes saves an annealing operation.

 

In Fig. 18 is shown an example of aluminum spinning. The article

illustrated is a cuspidor having a top 7¾ inches in diameter, a neck

with a 4-inch flare, a diameter at the top of 9½ inches, and a height

of 6½ inches. This shell was spun without annealing, which shows the

extreme ductility of aluminum. The copper shell shown in Fig. 19, has

a maximum diameter of 7 inches, and a depth of 8 inches; it was spun

with four annealings. A German silver reflector, which is 10 inches in

diameter at the largest end and 5 inches deep, is shown in Fig. 20.

The spinning of such a reflector, when made from this material, is

quite difficult. An open hearth cold-rolled steel shell with a maximum

diameter of 3 inches and a depth of 4 inches is shown in Fig. 21. This

shell was spun without annealing, which shows that the grade of steel

used is well adapted for this work.

 

[Illustration: Fig. 17. Gas Burner for Heating Spinning Chuck]

 

[Illustration: Figs. 18 and 19. Examples of Aluminum and Copper

Spinning]

 

[Illustration: Fig. 20. German Silver Reflector

 

Fig. 21. Open Hearth Cold-rolled Steel Shell]

 

In Fig. 22 two finished brass shells are shown to the right, and also

the number of operations required to change the form of the metal. The

upper shell is 6 inches long and 3½ inches in diameter at the large

end, while the lower one is 7¼ inches long by 3¾ inches in diameter.

It was necessary to anneal these shells between each operation, the

upper shell being annealed four times and the lower one three times.

These pieces were made in quantities sufficient to warrant the making

of chucks for each operation, which enabled them to be spun with less

skill than would be required if a finishing chuck only were made. When

a single finishing chuck is used, the various operations in spinning a

shell of this kind would be left to the judgment of the spinner, who

would decide the limit of the stretch of metal between the operations

before annealing.

 

[Illustration: Fig. 22. Various Steps in Spinning the Two Brass Shells

at the Right]

 

A brass shell that is made in five operations and with four annealings

is shown in Fig. 23. The finishing chuck used is a split or key chuck

on which it is necessary to cut out the end of the shell in order

to withdraw the key after the shell is spun. This shell, which is

shown finished to the right, is 5½ inches long. It is spun smooth

on a machine steel chuck, and is not skimmed, but gone over with a

planishing tool at the last operation. The two pieces shown in Fig. 22

were also finished in this way.

 

[Illustration: Fig. 23. Another Brass Spinning Operation; the Chuck

used is shown at A]

 

Fig. 24 shows a brass shell, which is a good example of “air spinning,”

so called because the finishing or second operation on part of the

shape is done in the air, thus avoiding the use of a sectional or split

chuck. The shell shown is about 5½ inches in diameter. The first or

breaking-down chuck is shown at _A_. The neck or small part of the

piece, and also a portion of the spherical surface, is formed by the

spinning tool without any support from the chuck. After the shell is

spun or broken down on chuck _A_, it is annealed and pickled. It is

then put back on chuck _A_ and planished or hardened on the part that

is to retain its present shape. The work is then placed on the chuck

_B_ and the soft part is manipulated by the tool until it conforms to

the shape shown to the right. While this soft part of the metal is

being formed, the part which was previously hardened retains its shape.

 

[Illustration: Fig. 24. An Example of “Air Spinning” and the Chucks

used]

 

 

Various Types of Metal-spinning Chucks and their Construction

 

A miscellaneous collection of spinning chucks is shown in Fig. 25. As

will be seen, the larger ones are machined out in the back to lighten

them, and also to give them an even balance. The larger of those

illustrated measure about 9½ inches in diameter, and they are made of

cast iron, while the smaller chucks shown in this view are of machine

steel. The chuck marked _A_ is a key chuck. Another collection of

spinning chucks of various shapes is shown in Fig. 26. Those in the

upper row are all key or split chucks, and the keys are shown withdrawn

from the sockets. All these chucks, up to 6 inches in diameter, are

made of machine steel; those seen in the lower row are shapes which are

comparatively easy to spin.

 

[Illustration: Fig. 25. Miscellaneous Collection of Spinning Chucks]

 

[Illustration: Fig. 26. Another Group of Spinning Chucks. Those in the

Upper Row are of the Split or Key Type]

 

A collection of hard maple chucks is shown in Fig. 27, some of which

represent shapes that are difficult to spin. The chuck _A_ is 15 inches

long, and the maximum diameter of _B_ is 12½ inches. These figures will

serve to give an idea of the proportions of the other chucks. All of

the chucks shown have threads cut in them and they are screwed directly

to the spindle of the lathe, the faceplate being dispensed with. Some

of the larger wooden chucks used measure approximately 5 feet in

diameter. A chuck of this size is built up of sections which are glued

together.

 

[Illustration: Fig. 27. Various Forms of Spinning Chucks made from Hard

Maple]

 

A number of bronze sectional split chucks are shown in Fig. 28. When

spinning over a sectional chuck, it is first necessary to break down

the shell as far as is practicable on a solid chuck. Care should be

taken, however, to leave sufficient clearance so that the work may be

withdrawn. The shell is then annealed, after which it is put on the

sectional chuck and the under cut or small end is spun down to the

chuck surface. When the entire surface of the shell is spun down to a

bearing, the shell is planished or skimmed to a smooth surface; the

open edge is also trimmed even and the shell is polished with emery cloth.