Metal Spinning 2

Metal Spinning 2

Followers

 

For holding the sheet metal blank to the spinning form, a block of wood

known as the follower, is used (see Fig. 6). Followers are made to

suit the shape of the work with which they are to be employed, always

being made with the largest possible bearing on the work; thus a shell

with a flat bottom twelve inches in diameter would be turned with the

aid of a follower having an 11¾-inch face, while a shell with a 4-inch

face would take a follower with a 3⅞-inch face. All shells do not have

flat bottoms, consequently, in spinning such as do not, it becomes

necessary to employ hollow followers. Hollow followers have their

bearing surfaces turned out to fit the ends of the forms with which

they are to be used. In practice, the blank is held against the end of

the spherical form with a small flat follower until enough of the shell

has been spun to admit of the hollow follower being used. All followers

are made with a large center hole in one end to receive the revolving

tail-center.

 

[Illustration: Fig. 6. Three Types of Followers]

 

In starting to spin a difficult shell it sometimes happens that the

necessarily small follower will not hold the blank. To prevent this

slipping, the face of the follower is covered with emery cloth. Often,

however, on rough work, the spinner will not stop to face the follower,

but will make a large shallow dent at the center of the blank; the

extra pressure required to force the metal against the form will

usually overcome the slipping tendency.

 

[Illustration: Fig. 7. Specimens of Metal Spinning]

 

 

Hand Tools

 

Hand tools, in great variety, form the principal asset of the spinner’s

kit. Spinning tools are made of tool steel forged to the required

shapes, and are hardened and polished on the working end. The round

steel from which they are made varies from ½ inch to 1½ inch in

diameter, according to the class of work upon which they are to be

used. The length of a spinning tool is about 2 feet, and it is fitted

into a wooden handle 2 inches diameter and 18 inches long, making the

total length of the handled tool about 3 feet, as shown in Fig. 8. As

the spinner holds this handle under the right armpit, he secures a

great leverage upon the work and is better able to supply the physical

power required to bring the metal to the desired shape.

 

[Illustration: Figs. 8 and 9. Spinning Tool and Swivel Cutter]

 

The commonest and by far the most useful of the spinning tools is

the combination “point and ball” which together with a number of

other tools, is shown in Fig. 11. This tool is used in doing the bulk

of the spinning operations--for starting the work and bringing it

approximately to the shape of the form. Its range of usefulness is

large on account of the many different shapes that may be utilized by

merely turning the tool in a different direction. Next in importance

comes the flat or smoothing tool which, as the name implies, is for

smoothing the shell and finishing any rough surfaces left by the point

and ball tool. The fishtail tool, so named from its shape, is used

principally in flaring the end of a shell from the inside, “spinning on

air,” as it is sometimes termed. This tool is used to good advantage in

any place where it is necessary to stretch the metal to any extent, and

its thin rounding edge proves useful in setting the metal into corners

and narrow grooves. Other tools are the ball tool which is adapted to

finishing curves; the hook tool, used on inside work; and the beading

tool which is needed in rolling over a bead at the edge of a shell when

extra strength or a better finish is desired.

 

When much beading of one kind is being done, a large heavy pair of

round-nose pliers (Fig. 10) with the jaws bent around in a curve and

sprung apart enough to allow for the thickness of the metal proves to

be a handy tool. After the edge of the shell has been flared out to

start the bead, the pliers are opened enough to admit the metal and

then closed and the stock guided around to form the bead as far as

possible. In this way the larger part of a bead is rapidly formed, one

jaw of the pliers acting as a spinning tool and the other corresponding

to the back-stick. During this operation, the pliers are, of course,

supported by being held against the T-rest.

 

[Illustration: Fig. 10. Spinners’ Pliers]

 

Closely allied with these spinning tools are two other tools (also

shown in Fig. 11) known as the diamond point and the skimmer. The

diamond point is for trimming the edges of the shell during the

spinning operation and for cutting out centers or other parts of the

work. The skimmer is for cleaning up the surface of a shell, removing a

small amount of metal in doing so, the amount depending upon the skill

the spinner used in the spinning proper.

 

[Illustration: Fig. 11. Hand Tools of Various Forms used in Spinning]

 

When the bottoms are to be cut from a large number of shells and it

is necessary that they be cut exactly alike, a tool known as a swivel

cutter is used. This tool (see Fig. 9) is simply an iron bar with a

cutter on one end, which swivels near the center around a pin in the

T-rest; thus by a slight movement of the arm the cutter is brought up

to the work, cutting a piece from the shell of exactly the same size

each time.

 

 

The Spinning Operation

 

In order to make clear the successive steps in spinning, let us briefly

consider the making of a copper head-light reflector, and the way the

work is handled when a few hundred pieces are to be made.

 

By trial spinning, the size of the blank required for one of the

reflectors is determined, and with the square shears the copper sheets

are cut into pieces an eighth of an inch larger each way. These squares

are then taken to the circular shears and cut to round shapes ready

for the spinning lathe. The spinning form, of kiln-dried maple, is

screwed to the spindle and the belt thrown to that step of the cone

pulley which will bring the speed nearest to 1,200 revolutions. From

the stock-room a follower is selected whose face will nearly cover the

bottom of the form. It is now “up to” the spinner. Holding a blank and

also the follower against the end of the form, he runs the tail-center

up to the center in the follower just hard enough to hold the blank

in place. Then, starting the lathe, he centers the blank by lightly

pressing against its edge a hard wood stick. As soon as it “lines up”

he runs the center up a little harder and clamps it in place. Some

spinners will “hop in” a blank with the lathe running, but this is

dangerous practice and sometimes the blank will go sailing across the

room. Often this happens in truing up the blank and for this reason it

is considered advisable to have a wire grating at the further side of

the lathe to prevent serious accidents; for a sheet metal blank is a

dangerous missile traveling at the high rate of speed which is imparted

to it by the lathe.

 

With a piece of beeswax (soap is sometimes used for economical reasons)

the spinner lightly rubs the rapidly revolving blank and then adjusts

the pin in the T-rest to a point near enough to the blank to obtain a

good leverage with the spinning tool. Holding the handle of his point

and ball tool under his right armpit and using the tool as a lever and

the pin on the rest as a fulcrum, he slowly forces the metal disk back

in the direction of the body of the form, never allowing the tool to

rest in one spot, but constantly working it in and out, applying the

pressure on the way out to the edge of the disk and letting up as he

comes back for a new stroke. In the meantime his left hand is busy

holding a short piece of hard wood (called the back-stick), firmly

against the reverse side of the metal at a constantly changing point

opposite the tool. The object of the back-stick is to keep the stock

from wrinkling as it is stretched toward the edge of the disk. Wrinkles

cause the metal to crack at the edges and for this reason they must be

kept from the stock as much as possible.

 

After a few strokes of the spinning tool have been taken, the shell

will appear about as shown at _B_, Fig. 12, and at this point it

is necessary to trim the shell at the edges with the diamond-point

tool. Trimming is required because spinning stretches the stock and

the resulting uneven edge will cause splits in the metal if it is

not trimmed occasionally. As a carpenter is known by his chips, so

a spinner is known by the way his work stretches. While the even

pressure of a good spinner will stretch the stock very little, the

uneven pressure of the inexperienced man will lead him into all sorts

of trouble on account of the way the stock will “go.” In either case

the metal always stretches least in the direction in which the sheet

stock was originally rolled, consequently giving the edge a slight

oval shape. In trimming zinc, the spinner holds a “swab” of cloth just

above the diamond point, to prevent the chips from flying into his

face and eyes--or those of his neighbors. With other metals the swab is

unnecessary.

 

The reflector is now taking shape. With each successive stroke the

spinner sets a little more of the metal against the form. Not only does

spinning stretch the metal, but it hardens it as well; therefore, at

the stage _C_ it becomes necessary to anneal the partially completed

reflector, which is done by heating it to a low red in a gas furnace.

In running through a lot of shells, the common practice is to spin them

all as far as possible without annealing, and after annealing the whole

lot, to complete the spinning.

 

[Illustration: Fig. 12. Successive Steps in Spinning a Reflector]

 

After replacing the shell upon the form, it is trimmed and worked

further along the form, gradually assuming the appearance shown at _D_.

At this time, the spinner goes back to the small radius at the front

end of the shell and with a ball tool he closes the annealed metal hard

down against the form, for the spinning has tended to pull the stock

slightly from the form at this point. The body of the reflector is now

practically completed and the spinner directs his attention to rolling

the bead at the outside edge. Slowly he begins to roll the edge of the

shell back, using his hook tool to complete the bead as far as possible

and exercising care to keep the back-stick firmly against the metal

so as to keep the wrinkles out. Now, with the diamond point, he gives

the edges a final trim, and with the beading tool closes down the bead

snugly against the rest of the shell, as shown at _E_. Lastly, the

swivel cutter is placed in the proper hole of the T-rest and a turn of

the tool cuts out the center to the exact size, and the reflector is

completed. If any burrs or rough places remain they are easily removed

at this time with the skimmer or diamond point, and a little emery cloth gives the shell a finished appearance.