Metal Spinning 5

Metal Spinning 5

A large bronze chuck of seven sections, one of which is a key section,

is shown at _A_. The largest diameter of this chuck is 10 inches. It

has a cast iron center hub and a steel cap at the top for holding the

sections in place. This cap, when in place in the retaining groove

shown, is flush with the top of the chuck. Another large chuck having

five sections and one key section is shown at _B_. The retaining cap in

this case is of a different form. The lower parts of the sections of

all these chucks fit in a groove at the bottom of the hub. A chuck of

five sections that is without a binding cap, is shown at _C_. This is

not a good design as the hub or center is too straight, and all of the

grip or drive is from the bottom groove, which is not sufficient. The

shape shown at _D_ is more difficult to spin than any of the others,

as it is smaller at the opening in proportion to its size. This chuck

also requires more sections in order that it may be withdrawn from the

shell after the latter is spun. The chuck _E_ is intended for a small

shell that is also difficult to spin. The drive pins which prevent the

segments of the chuck _E_ from turning may be seen projecting from its

base. The centering pins at the outer end of chucks _D_ and _E_ and the

binding caps may also be seen. The chuck _A_, because of its size, is

hollowed out to reduce the weight. All of these chucks were made for

hard service, and they have been used in spinning thousands of shells.

 

Another group of sectional chucks is shown in Fig. 29. They are mostly

made from hard maple. The sections of chuck _A_ are planed and fitted

together and thin pieces of paper are glued to these sections before

they are glued collectively for turning. By using the paper between

the joints, the sections may be easily separated after they are turned

to the proper size and form. If the different sections were glued

without paper between them, the joint formed would be so good that the

separation of the sections could not be controlled, and parts from

opposite sections would be torn away. The use of the paper, however,

between the glued joints, controls the separation of the sections. The

chuck shown at _D_ is also made with the paper between the sections.

Chucks _B_ and _E_ are turned from the solid, care being taken to have

the grain of the wood lengthwise. After they are turned to the required

form, they are split into sections with a sharp chisel. Before doing

this, the key-section should first be laid out. There should be as few

sections as possible, the number being just sufficient to enable the

withdrawing of the chuck from the shell after the latter is spun to

shape. This method of making a chuck, while quicker than the other, is

not good practice, except for small work.

 

[Illustration: Fig. 29. Sectional Chucks made from Wood]

 

A lignum vitæ chuck is shown at _A_ in Fig. 30; this was made with

paper between the sections. The key-section is shown on top. This wood,

while being more durable than hard maple, costs sixteen cents a pound

in the rough and, counting the waste material, is not any cheaper

than bronze, and is less durable. The hard maple chucks _B_ and _C_

were turned from the solid, after which the sections were split. The

segments shown in the center of the illustration did not split evenly,

owing to a winding or twisting grain.

 

[Illustration: Fig. 30. Other Examples of Wooden Sectional Chucks]

 

The construction of a sectional spinning chuck is shown in Fig. 31.

This illustration also shows the proper proportion for the central hub

and its taper. This hub should never be straight, but should have from

5 to 7½ degrees taper on the central part. There should also be a taper

of 1½ degree on the other binding surfaces as indicated. These parts

are made tapering so that the shell can be released from the lathe

after spinning, without hammering or driving; when straight surfaces

are used the work has to be pried off, and it is also harder to set

up the sections for the next shell. Another disadvantage is that with

straight fittings the wear cannot be taken up. An end cap or binder

should be used wherever possible as it steadies the chuck. A drive pin

should also be used and the hole for it drilled in the largest section;

this is important, as it gives the sections a more positive drive. If

they slip they will soon wear themselves loose and leave openings at

the joints.

 

[Illustration: Fig. 31. Elevation and Plan showing Construction of

Sectional Chuck]

 

The plan view shows the method of laying out the various sections. The

key should be laid out first. One key is enough for the particular

form of chuck illustrated, but it is often necessary to use two key

sections when the shell opening is small.

 

When a sectional chuck is to be made, it is important to decide first

on the size of the central hub _A_, the number of sections _C_, and

also the design of the cap or binder _B_. This cap must not exceed in

size the opening in the finished shell, as it would be impossible to

remove it after the chuck sections were taken out. After the size of

the hub _A_ has been decided upon, a wooden form should be turned that

is a duplicate of _A_, except that a spherical surface _E_ should be

added. This spherical part should be slightly smaller than the inner

diameter of the bronze sections in order to allow for machining them.

In turning this wooden pattern on which the plaster patterns for the

sections are to be formed, the shoulder _D_ should be omitted, as a

removable metal ring will take its place.

 

When the wooden hub is ready, two metal partitions or templets of the

same outline as the chuck, though about one-half inch larger than its

total diameter, for shrinkage and finishing, are fastened to the hub in

the correct position for making a plaster pattern for the key section.

These patterns should have extension ends so that the sections when

cast may be held by them while they are being turned. The templets

should be banked around with a wad of clay, and they should also be

coated on the inside with sperm oil to keep the plaster from sticking.

There should be two brads driven in the hub for each section of plaster

to hold the sections in place while they are being turned. After the

plaster for the key section has hardened, the templets should be

located one on each side of the key section, so that the two adjacent

sections may be made. In this way all the sections are finished. After

about forty-eight hours the plaster will be hard enough to turn in the

lathe with a hand tool. The form should be roughly outlined and plenty

of stock left for shrinkage, as bronze shrinks considerably. Before

taking the sections off the wooden frame, the metal band _D_ should be

removed to allow the sections to be separated. This should not be done,

however, until they are numbered, so that they can be again placed in

their proper positions. After the sections are cast, they should be

surfaced on a disk grinder, or finished with a file, care being taken

to remove as little metal as possible. Each section is next tinned on

both contact faces, and then all are assembled and sweated or soldered

together by a blow-pipe. It is sometimes necessary to put a couple of

strong metal bands around the sections to hold them firmly in place

when soldering and also to support them during the turning operation.

 

[Illustration: Fig. 32. A Modern Spinning Lathe]

 

The central hub _A_ should be machined first; then the assembled

outside shell should be machined to fit the hub _A_, both on the

taper part and at the point _D_. While the segments are being bored

and faced, they are held by the extension ends (not shown) which were

provided for this purpose. This outer shell should also be machined all

over the inside so that it will be in balance. It is then taken out of

the chuck and a hole is drilled in the largest section for drive pin

_H_. The hub _A_ is then caught in the lathe chuck with the assembled

sections on it, and a seat is turned for the cap _B_. After this is

done the binder bands can be removed, but not before. The chuck can be

finished with a hand tool and file after the roughing cut is taken.

After the sections are removed from the hub and numbered at the bottom

or inner ends, they can be separated by heating them. If the joints are

properly fitted there will be only a thin film of solder, which can be

wiped off when hot.

 

A twenty-four-inch metal spinning lathe that is rigged up in a modern

way, is shown in Fig. 32. The hand wheel of the tailstock has been

discarded for the lever _A_, which is more rapid and can be manipulated

without stopping the lathe. This lathe has a roller bearing for the

center _B_ which is a practical improvement over types previously used.

The pin _C_, which is used in the rest as a fulcrum for the spinning

tools, is also an improvement, being larger than those ordinarily

used. It is ¾ inch in diameter, 6 inches long, and it has a reduced

end for the holes in the rest, ⅜ inch in diameter by 1 inch long. This

pin is large enough so that the spinner can conveniently hold it with

his left hand when necessary, and it can also be rapidly changed to

different holes. The pins ordinarily used, because of their small size,

do not have these advantages. The speed of a spinning lathe having a

five-step cone should be about 2,250 to 2,300 revolutions per minute

with the belt on the smallest step, and from 600 to 700 revolutions per

minute with the belt on the largest step. The fastest speed given is

suitable for all work under 5 inches in diameter, and the slowest for

work within the capacity of the lathe. On large shells it is sometimes

necessary to change from one speed to another as the work progresses.

Figs. 33 and 34 show the spinner at work, and illustrate how the tool

should be held, and also the proper position of the left hand.

 

[Illustration: Fig. 33. View showing how the Tool is held when Spinning]

 

[Illustration: Fig. 34. Another View showing the Position of the

Spinner and the Way the Tool is held when forming the Metal]

 

 

Construction of the Tailstock and Back-center

 

Fig. 35 shows a spinning-lathe tailstock, which has been changed from

the hand-wheel-and-screw type to one having a lever and a roller

bearing. The spindle _A_ which is withdrawn from the lever and turned

one-quarter of a revolution to give a better view of the rollers, is

made from 1¾-inch cold rolled steel. The rollers against which the

center bears do not project beyond the spindle, so that the latter

can be withdrawn through the tailstock. This eliminates the excessive

overhang caused by ball bearings and other centers. When the center

projects too far, the tailstock cannot be set close to the work owing

to the necessity of withdrawing the center when removing the spun part.

The application of this principle to a spinning lathe is original and

the type of center illustrated was used only after all other kinds

had failed, including all the types of ball bearings and revolving

pins. The best forms of ball bearing centers do not last over a year,

if in constant use, and they will not always revolve on small work.

Two other spindles are shown in this engraving, which were taken

from other lathes in order to show different views of the parts. The

cylindrical pieces _B_ are the hardened friction rollers which belong

in the slot of the spindle _F_, and _C_ is the hardened pin upon which

they revolve. The hardened center _D_ has a threaded end on which the

back-centers _E_ of different lengths and shapes are screwed. The friction rollers should always be in a vertical position, and care should be taken to have them exactly central with the spindle.